THE INCIDENCE OF MAJOR 
LEPIDOPTERAN PESTS ON CABBAGE 
AND THEIR ASSOCIATED PARASITOIDS
IN GHANA
By
MILLICENT ASAABA COBBLAH
b  I t cz
THE INCIDENCE OF MAJOR LEPIDOPTERAN PESTS 
ON CABBAGE AND THEIR ASSOCIATED  
PARASITOIDS IN GHANA
This Thesis is Submitted to the University o f Ghana, Legon, 
in Fulfillment o f the Requirements for the Award o f 
Doctor o f Philosophy (Ph. D.) Zoology Degree.
By
Millicent Asaaba Cobblah 
B.Sc. Honours (Zoology), University o f Ghana, Legon. 
Postgraduate Diploma & M.Sc. (Applied Insect Taxonomy), 
University o f Wales, Cardiff United Kingdom.
Department o f Animal Biology 
and Conservation Science,
Faculty o f Science,
University o f Ghana,
Legon.
August, 2009
DECLARATION
I hereby declare that the work herein submitted as a thesis for the Doctor of Philosophy 
Degree in Zoology (Entomology) is the result of my own investigations and has not been 
submitted for a similar degree in any other University.
MILLICENT ASAABA COBBLAH
(Ph.D. Candidate)
DATE
"T, 2o / /
DATE....
DEDICATION
To my daughter Amanda Aku Ahornam Awadey who I left several times as a little girl to 
carry out this work and to my family who took care of Amanda when I had to travel.
. r' Y  x
! I
ACKNOWLEDGEMENTS \  j
I wish to acknowledge the National Agricultural Research Programme (NARP) of the 
CSIR Ghana, the USA Embassy (Fulbright Scholarship), the FAO/UNDP Farmer Field 
Schools Programme, and the University of Ghana (Leventis Scholarship) for providing the 
funds to cany out this study.
I specially thank my supervisors: Prof. Kwame Afreh - Nuamah (Institutes of 
Agricultural Research), Dr. D. D. Wilson and Prof. E. 0 . Owusu (Department of Animal 
Biology and Conservation Science, DABCS), all of the University of Ghana.
I am grateful to the specialists at CABI Bioscience, U.K for identification and 
confirmation of the parasitoids and pests, Dr. Virendra Gupta under whom I worked for one 
year whilst on the Fulbright Scholarship and Dr. Butler who assisted with photography of the 
parasitoids, both of the Department of Entomology and Nematology. University of Florida. 
USA, Drs. J. Okine and E. R. Mitchell of the USDA, Gainesville, Florida who assisted with 
explanation on parasitoid biology. My gratitude goes to the staff of WEICO. Weija for 
providing the land and other resources for field work. 1 am also indebted to Ms. Joyce 
Heflide and, Messrs. Adzo and Aboah for assistance in the field and laboratory work, Mr. F. 
Ansah, the chief technician, Mr. F. Sekou of Botany Department and Prof. Chris Gordon 
(VBRP) who assisted with aspects of the photography. I cannot forget the role played by my 
loyal friend the late Mr. S. Mensah a technician of the then Department of Zoology who 
worked tirelessly with me in the field at Weija. My gratitude goes to the following: Prots. 
Obeng-Ofori and Ntiamoah-Baidoo, Drs. Bimi and Darpaah. I appreciate the assistance given 
by Mr. Osae of BNARI, GAEC and Mr. Avicor (ARPP1S) in the use of the SPSS software 
and sharing their knowledge in the statistical analysis and graphics. Finally, 1 thank Mr. E. 
Nyarko of the Ghana Science Association Secretariat, Legon, for typesetting this thesis.
v
COPYRIGHT
All rights reserved. No part of this thesis may be reproduced, stored in any retrieval 
system or transmitted in any form or by any means; electronic, mechanical, recording or 
otherwise, without prior written permission from the author or the University of Ghana, 
Legon.
vi
ABSTRACT
The study was carried out at the Weija Irrigation Company site at Tubaman, Weija, 
the Laboratories of the Department of Zoology (now Department of Animal Biology and 
Conservation Science, DABCS), University of Ghana, Legon and some selected districts of 
Ghana. It was designed to; identify and establish the major Lepidopteran pests on cabbage, 
Brassica oleracea (L.) var. capitata and their parasitoids, determine the effect of the 
commonly used insecticides on parasitism and the biology of the major parasitoid, describe 
and illustrate the pests and their parasitoids to aid in identification. The rationale for the 
study was to provide information for implementation of effective integrated pest management 
in cabbage production in Ghana.
Field studies were carried out at the Weija site for three years. The design of the 
experiments was a randomized complete block design. Indirect and direct methods were used 
to investigate the effect of four insecticides namely, a synthetic pyrethroid (Karate), a 
Bacillus thuringiensis formulation, neem seed water extract and a commercial neem 
formulation, (Neemazal) on the major parasitoid. The illustrations were made using the 
scanning electron microscope, photomicroscope, a digital camera and Camera Lucida 
drawings.
The pests recorded were Plulella xylostella L., Trichoplusia rti (Hvibner). Hellula 
undalis (F), Helicoverpa armigera (HUbner) and Spodoptera littoralis (Boisduval). Plulella 
xylostella was the most abundant pest recorded during the study period. There was no 
significant difference between its larval density per plant in the major rainy season (0.15 ±
0.04, p > 0.05) compared with the minor rainy season (0.20 ± 0.07, p > 0.05): and also 
between the minor rainy season and the dry season (0.29 ± 0.5, p > 0.05). On the other hand, 
T. ni was only abundant during the major rainy season. There was a significant difference
between larval density per plant during this season (0.60 ± 0.11, p < 0.05) compared with the 
other seasons. With regard to S. litloralis, there was a significant difference between its 
larval density per plant in the minor rainy season (0.39 ± 0.10, p < 0.05) compared with the 
other seasons. The other pests occurred in insignificant numbers.
Out of the 15 species of parasitoids recorded from the pests, 7 were identified to the 
species level, 6  to the generic level and 2 to species groups. Seven of the species: Charops 
sp.. Brachymeria sp.. Hockeria sp., Elasmus sp., Notanisomorphella sp., Tetrastichus 
atriclavus S.L., Pediobius sp. and Trichomalopsis sp. were recorded for the first time in 
Ghana and may also be new species. The major parasitoid was Cotesia plutellae 
(Kurdjumov) which accounted for 92% and 60.9% of the parasitoids recorded from P. 
xylosiella and T. ni, respectively. The second important parasitoid was Euplectrus 
laphygmae (Ferriere) and it was specific to T. ni and S. litloralis. The facultative 
hyperparasitoids of P. xylostella were Oomyzus sokolowskii (Kurdjumov), Elasmus sp.? 
Aphanogmus reticulatus (Fouts) and Trichomalopsis sp. via C. plutellae. Blepharella vasta 
(Karsh), Peribaea orbata (Wiedemann), Notanisomorphella sp and Chelonus cunirnaculaliis 
(Cameron) were specific to the larvae of S. littoralis. No parasitoids were recorded from H. 
armigera. No egg parasitoid was observed.
There was seasonal variation in parasitism of P. xylostella by C. plutellae. The rate of 
parasitism (68 .6  ± 12.9%, p < 0.05) was significantly highest in the major rainy season and 
significantly least (9.9 ± 7.1 %, p < 0.05) in the minor rainy season. The rate of parasitism of 
P. xylostella by C. plutellae did not differ among the unsprayed and insecticide treated plots. 
However, adult C. plutellae emerging from pests collected from 'Karate' treated plots 
sometimes died in the process of eclosion or were short - lived. Neem seed water extract 
applied at 50 g/l also adversely affected the ability of the parasitoid larva to spin its cocoon 
for pupation. Of the three insecticides. ‘Karate’ was the most toxic causing 100% mortality
to the adult Cotesia pluiellae within ten seconds of direct exposure. Neemazal and Bt. 
applied at 1.0% and 1 .Og/liter of water respectively, were the least toxic to the adult.
It is concluded that P. xylostella is the major pest of cabbage in Ghana, while T. ni 
and S. littoralis are abundant only during the major and minor rainy seasons respectively. 
Cotesia pluiellae and E. laphygmae are the major parasitoids and they should be considered 
in the development of any integrated pest management on cabbage. Karate has a harmful 
effect on C. pluiellae adults. Even though, Neem seed applied at 50g/I adversely affected the 
development of C. pluiellae, lower doses, or Bacillus thuringiensis formulations could be 
applied in the development of an Integrated Pest Management programme on cabbage.
TABLE OF CONTENTS
DECLARATION................................................................................................................ ««
DEDICATION.................................................................................................................... iv
ACKNOWLEDGEMENTS...............................................................................................  v
COPYRIGHT..................................................................................................................... vi
ABSTRACT....................................................................................................................... vii
TABLE OF CONTENTS..................................................................................................  x
LIST OF TABLES.............................................................................................................. xvi
LIST OF FIGURES............................................................................................................ xvii
LIST OF PLATES.............................................................................................................. xviii
CHAPTER ONE............................................................................................................... I
1.0 GENERAL INTRODUCTION.......................................................................  1
CHAPTER TWO.............................................................................................................  6
2.0 LITERATURE REVIEW................................................................................. 6
2.1 Insect Pests of Cabbage.................................................................................... 6
2.2 Origin and Distribution of the Pests................................................................  10
2.3 Description of the Pests.................................................................................... 11
2.4 Life History of the Pests................................................................................... 13
2.5 Host Range of the Pests....................................................................................  16
2.6 Damage by the Pests to Cabbage.....................................................................  1 g
2.7 Seasonal Incidence of the Pests........................................................................ 20
2.8 Mortality Factors Influencing the Survival of the Pests.................................. 23
2.8.1 Plutella xylostella.............................................................................................  23
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€j*J *
K- vHjv;
2.8.1.1 Rainfall , ^ T . ..........................  24
2.8.1.2 Parasitoids..............................................................................................................  24
2.8.2 Trichoplusia ni.......................................................................................................  27
2.8.2.1 Parasitoids..............................................................................................................  27
2.8.2.2 Nuclear Polyhedrosis Virus..................................................................................  27
2.8.3 Hellula undalis.......................................................................................................  28
2.9 Control Measures Against the Pests....................................................................  28
2.9.1 Chemical Control...................................................................................................  28
2.9.2 Biological Control................................................................................................. 31
2.9.3 Integrated Pest Management.................................................................................  37
CHAPTER THREE.............................................................................................................. 40
3 0 SEASONAL VARIATION OF PARASITOID-HOST ASSOCIATIONS
AND EFFECT OF INSECTICIDES..................................................................  40
3.1 Introduction............................................................................................................  40
3.2 Materials and Methods.........................................................................................  41
3.2.1 The Experimental Site .........................................................................................  41
3.2.2 Planting.................................................................................................................  42
3.2.3 The Experimental Layout.....................................................................................  43
3.2.4 Treatments Applied..............................................................................................  43
3.2.5 Fertiliser Application............................................................................................  44
3.2.6 Insecticide Application.........................................................................................  44
3.2.7 Incidence and Seasonal Abundance of Pests and Parasitoids.............................. 46
Table of Contents Cont’d. f c / ]:< i,
xi
Table o f Contents Cont'd.
3.2.8 Laboratory Rearing of Pests............................................................................. 47
3.2.9 Weekly Parasitism Trends by Cotesia pluiellae and Euplectrus laphygmae
in Relation to Plutella xylostella and Trichoplusia ni ..................................  47
3.2.10 Identification of Pests and Parasitoids.............................................................. 48
3.2.11 Emergence and Mortality of Cotesia plutellae Exposed to Insecticides  48
3.2.12 Laboratory Studies on Mortality of Adults and Emergence of Pupae of
C. pluiellae Exposed to Different Insecticides............................................  49
3.2.12.1 Filter Paper Method..........................................................................................  49
3.2.12.2 Direct Application Method............................................................................... 50
3.2.13 Statistical Analysis............................................................................................  51
3.3 Results............................................................................................................... 52
3.3.1 Incidence and Seasonal Abundance of Lepidopteran Pests............................  52
3.3.2 Comparative Abundance of Larvae of Lepidopteran Pests on
Unsprayed Experimental Plots and on Farmer’s Plots at Weija.................... 55
3.3.3 Population Density of Larvae of P. xylostella, T. ni and 5. littoralis on
Cabbage in the Three Seasons on Experimental Plots...................................  56
3.3.4 Incidence and Seasonal Abundance of the Parasitoids................................... 57
3.3.5 Weekly Parasitism Trends by C. pluiellae in Relation to P. xy lostella  60
3.3.6 Weekly Parasitism Trends by C. pluiellae and E. laphygmae in Relation
to T. ni..............................................................................................................  63
3.3.7 Parasitism of P. xylostella by C. plutellae in Three Seasons..........................  64
3.3.8 Parasitism of P. xylostella by C. pluiellae on Insecticide Treated Plots  64
Page
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Table o f Contents Cont’d.
3.3.9 Parasitism of T ni by C. plutellae and E. laphygmae in the Major
Rainy Season...................................................................................................  65
3.3.10 Parasitism of T. ni by C. plutellae and E. laphygmae on Insecticide
Treated Plots....................................................................................................  65
3.3.11 Emergence of C. plutellae Adults from Field Parasitised Pests ....................  66
3.3.12 Emergence of C. plutellae Adults Collected as Pupae Exposed to
Different Insecticides in the Field...................................................................  67
3.3.13 Mortality of C. plutellae Adults and Emergence of Pupae Exposed to
Insecticides in the Laboratory.........................................................................  68
3.4 Discussion..........................................................................................................  69
CHAPTER FOUR...........................................................................................................  79
4.0 BIOLOGY AND ECOLOGY OF THE PARASITOIDS OF
LEPIDOPTERAN PESTS OF CABBAGE.................................................... 79
4.1 Introduction........................................................................................................ 79
4.2 Materials and Methods.....................................................................................  81
4.2.1 Field Sampling and Rearing of Host -  Plutella xylostella.............................. 81
4.2.2 Field Collection and Rearing of Parasitoids....................................................  82
4.2.3 Life History and Lifestyle Studies of Cotesia plutellae ................................. 82
4.2.4 Longevity Studies of Cotesia plutellae............................................................  83
4.2.5 Oviposition Preference of Plutella xylostella Larvae by Cotesia plutellae... 84
4.2.6 Field Observations on Biology and Ecology of the Parasitoids ....................  84
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Table o f Contents Cont’d.
4.3 Results..............................................................................................................  85
4.3.1 Biology and Ecology of Cotesia plutellae...................................................... 85
4.3.1.1 Life History and Lifestyle of C. plutellae....................................................... 85
4.3.1.2 Longevity of Mated and Unmated Adult Cotesia plutellae............................ 87
4.3.1.3 Oviposition Preference of Plutella xylostella Larvae by Cotesia plutellae... 87
4.3.1.4 Field Observations on Parasitism by C. plutellae...........................................  88
4.3.2 Biology' and Ecology of Other Parasitoids...................................................... 90
4.4 Discussion.........................................................................................................  98
CHAPTER FIVE.............................................................................................................  104
5.0 DESCRIPTION OF STAGES OF LEPIDOPTERAN PESTS.
BEHAVIOUR AND DAMAGE.....................................................................  104
5.1 Introduction.......................................................................................................  104
5.2 Materials and Methods....................................................................................  105
5.2.1 Rearing of Lepidopteran Pests........................................................................  105
5.3 Results..............................................................................................................  106
5.3.1 Description of Stages of Lepidopteran Pests, Behaviour and Damage  106
5.3.1.1 Plulella xylostella (Linnaeus).........................................................................  106
5.3.1.2 Trichoplusia ni (HUbner).................................................................................  I l l
5.3.1.3 Spodoptera littoralis (Boisduval)....................................................................  114
5.3.1.4 Helicoverpa armigera (HUbner).....................................................................  1 ] 9
5.3.1.5 Hellula undalis Walker....................................................................................  121
5.3.1.6 Spoladea recurvalis (Fabricius)......................................................................  123
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Table o f Contents Cont’d.
5.4 Discussion......................................................................................................... 124
CHAPTER SIX................................................................................................................. 127
6.0 DESCRIPTION OF PARASITOIDS OF THE LEPIDOPTERAN
PESTS OF CABBAGE..................................................................................  127
6.1 Introduction....................................................................................................... 127
6.2 Materials and Methods....................................................................................  129
62 .1 Identity and Description of Parasitoids............................................................ 129
6  2.2 Scanning Electron Microscopy........................................................................ 130
6.2.3 Photomicroscopy.............................................................................................  131
6.3 Results..............................................................................................................  132
6.3.1 Identity of the Parasitoids................................................................................  132
6.3.2 Descriptions of the Parasitoids........................................................................  133
6.3.2.1 Ichneumonoidea............................................................................................... 133
6.3.2.2 Chalcidoidea..................................................................................................... 142
6.3.2.3 Ceraphronoidea................................................................................................  169
6.3.2.4 Muscoidea.........................................................................................................  172
6.4 Discussion.........................................................................................................  173
CHAPTER SEVEN.........................................................................................................  182
7.0 GENERAL CONCLUSIONS AND RECOMMENDATIONS....................  182
7.1 Conclusion........................................................................................................ 182
7.2 Recommendations............................................................................................  ] 85
REFERENCES CITED..................................................................................................... 187
APPENDICES...................................................................................................................  224
Page
xv
LIST OF TABLES
Table 2.1: Major Pests of Cabbage and Damage Worldwide..................................... - 9
Table 3.1: Volumes of Insecticides Applied to Cabbage Plants................................. - 45
Table 3.2: Relative Abundance of Larvae of Lepidopteran Pests of Cabbage
in the Three Cropping Seasons on the Unsprayed Plots at the
Experimental Site, Weija........................................................................... - 54
Table 3.3: Relative Abundance of Larvae of Lepidopteran Pests of Cabbage
in the Three Cropping Seasons on Farmer’s Plots at Weija.....................- 55
Table 3.4: Comparative Percentage Abundance of Lepidopteran Pests on
Experimental Plots and on Farmer’s Plots.................................................- 56
Table 3.5: Population Density per Plant of Larvae of P. xylostella, T. ni and
S. littoralis on Cabbage in the Three Seasons...........................................- 57
Table 3.6: Seasonal Occurrence of Parasitoid/Hyperparasitoid Species and
Lepidopteran Host Species on Cabbage at the Experimental Site............- 58
Table 3.7: Mean Percentage Parasitism of P. xylostella by C. plutellae on
Different Treatments in the Three Seasons...............................................- 65
Table 3.8: Mean Percentage Parasitism of T. ni by C. plutellae and
E. laphygmae on Different Treatments in the Major Rainy Season.........- 65
Table 3.9: Emergence of C. plutellae Adults Reared from Field Parasitized
P. xylostella from the Different Treatments in the Three Seasons...........- 66
Table 5.1: Percentage of Eggs Laid in a Batch by P. xylostella in the Field..............- 106
Table 6.1: Identity of the Parasitoids / Hypcrparasitoids Recorded from the
Lepidopteran Pests on Cabbage................................................................   j 32
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LIST OF FIGURES
Figure 3.1: Distribution Map of Pests of Cabbage in Southern Ghana........................ - 53
Figure 3.2: Trophic Relationships among P. xylostella, T. ni and Parasitoids and
Hyperparasitoids on Cabbage.....................................................................- 60
Figure 3.3: Weekly Parasitism Trends by C. plutellae in Relation to P. xylostella
in the Major Rainy Season. Coefficient of Correlation r = 0.97............- 61
Figure 3.4: Weekly Parasitism Trends by C. plutellae in Relation to P. xylostella
in the Minor Rainy Season. Coefficient of Correlation r = 0.55 ...........- 61
Figure 3.5: Weekly Parasitism Trends by C. plutellae in Relation to P. xylostella
in the Dry Season. Coefficient of Correlation r = 0.66.......................... - 62
Figure 3.6: Weekly Parasitism Trends by C. plutellae and E. laphygmae in
Relation to T. ni in the Major Rainy Season.............................................. - 63
Figure 3.7: Seasoned Variation in Mean Percentage Parasitism of P. xylostella
by C. plutellae............................................................................................. - 64
Figure 3.8: Emergence of both C. plutellae and E. laphygmae Adults from Field
Parasitized T. ni from the Different Treatments in the Major
Rainy Season.............................................................................................. - 67
Figure 3.9: Percentage Emergence of C. plutellae Adults Collected as Pupae
from the Different Treatments.................................................................... - 68
Figure 3.10: Mortality of Adults and Pupae of C. plutellae Exposed to Different
Insecticides.................................................................................................. - 69
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LIST OF PLATES
Plate 4.1: Newly emerged C. plutellae larva (arrowed) and ho s t..............................- 86
Plate 4.2: C. plutellae pupa (arrowed) and host..........................................................* 86
Plate 4.3: Unparasitised P. xylostella larva [xlO ].......................................................- 86
Plate 4.4: Empty pupal cocoon of C. plutellae (arrowed).......................................... - 86
Plate 4.5: Carcass of P. xylostella after parasitism..................................................... - 87
Plate 4.6: Pupa of Charops sp [x 12] hanging by thread after emergence of
adult parasitoid............................................................................................ - 91
Plate 4.7: Newly hatched larvae of E. laphygmae [x 2.7] (arrowed) penetrating
host to feed................................................................................................. - 93
Plate 4.8: Larvae of E. laphygmae (arrowed) about to migrate to pupate................. - 93
Plate 4.9: Mature larva of E. laphygmae migrating (arrowed) down the
host to pupate.............................................................................................. - 93
Plate 4.10: Carcass of T. ni larva after parasitism by E. laphygmae ..........................- 94
Plate 4.11: Adult B. sp. nr. vasta [x 2.5] and pupal case of S. litloralis from which
it had emerged............................................................................................. - 97
Plate 4.12: Adult P. orbata [x 14] and its pupal case....................................................- 98
Plate 5.1: Eggs of P. xylostella [x 6 ] on cabbage leaf................................................ - 107
Plates 5.2: Mature larvae of P. xylostella [x 3] and damage on cabbage leaf,
faeces are arrowed......................................................................................- 108
Plate 5.3a: Pre-pupa of P. xylostella [x 6 ] ..................................................................... - 109
Plate 5.3b: Mature Pupa of P. xylostella (x 4]............................................................. 109
Plate 5.4: Adult P. xylostella (A-Female [x 3.8], B-Male [x 3.5])........................... - 110
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List o f Plates Cont'd.
Plate 5.5: Mature larva of T. ni [x 4.8]........................................................................" * * 3
Plate 5.6: Freshly pupated T. ni [x 3.7]........................................................................ • • ' 3
Plate 5.7: Adult of T. ni [x 4.0].................................................................................... - 113
Plate 5.8: Egg mass of S. littoralis[x 12].....................................................................- 114
Plate 5.9a-d: Variable colouration in young larvae of S. littoralis..................................- 115
Plate 5.10: Mature caterpillar of S. littoralis [x 3.5].................................................... - 116
Plate 5.11: Larva of S. littoralis [x 2.0] (arrowed) feeding on cabbage head............... - 117
Plate 5.12: Pupa of S. littoralis [x 5] spine arrowed..................................................... - 118
Plate 5.13: Adult of S. littoralis [x 2.7].........................................................................- 118
Plate 5.14a: Larva of H. armigera [x 1.5].......................................................................- 120
Plate 5.14b: Larva of H. armigera [x 1.7].......................................................................- 120
Plate 5.15: Adult of H. armigera [x 2 ] ..........................................................................- 121
Plate 5.16: Larva of H. undalis [x 2.2].......................................................................... - 122
Plate 5.17: Adult of H. undalis [x 3.6]...........................................................................- 123
Plate 5.18: Adults of S. recurvalis [x 2.0].....................................................................- 124
Plate 6.1a: Wing illustration of terminologies...............................................................- 130
Plate 6 .1 b: Antenna illustration of terminologies......................................................... - 130
Plate 6.2: Female Cotesia plutellae [x 13]................................................................... - 133
Plate 6.3: Schematic diagram of fore-wing and hind-wing of C. plutellae [x 17]...- 134
Plate 6.4 a: Schematic diagram of antenna of male C. plutellae [x 20]-.................... 135
Plate 6.4 b: Schematic diagram of antenna of female C. plutellae [x 20] .................. - 135
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List of Plates Cont’d.
Plate 6.5a: Scanning electron micrograph of female antenna [x 240]..........................- 136
Plate 6.5b: Scanning electron micrograph of male antenna [x 300].............................- 136
Plate 6 .6 : Scanning electron micrograph of facial view of C. plutellae [x 110]......- 137
Plate 6.7a: Scanning electron micrograph dorsal view of mesosoma [x 90]............... - 138
Plate 6.7b: Scanning electron micrograph lateral view of mesosoma [x 66 ] .............. - 138
Plate 6 .8  a: Adult Chelonus curvimaculatus [x 4.0]......................................................- 140
Plate 6 .8  b: Schematic diagram of C. curvimaculatus [x 15] to show carapace - 140
Plate 6.9: Female Charops sp. [x 7.0]......................................................................... - 141
Plate 6.10: Fore and hind wings Charops sp. [x 16].....................................................- 142
Plate 6.11: Female Brachymeria sp. [x 20]..................................................................- 143
Plate 6.12: Female Hockeria sp. [x 40]........................................................................ - 144
Plate 6.13: Schematic diagram of fore-wing of Hockeria sp. [x 40]........................... - 145
Plate 6.14: Adult male [x 17.5] and female [x 16] Elasmus sp.................................... - 146
Plate 6.15: Schematic diagram of antenna of female Elasmus sp. [x 120]....................- 147
Plate 6.16: Schematic diagram of hind leg of Elasmus sp. [x 55]............................... - 148
Plate 6.17: Schematic diagram of forewing of female Elasmus sp. [x 40]................ - 148
Plate 6.18: Adult male Elasmus sp. to show branched antennae [x 30].......................- 149
Plate 6.19: Male [x 44] and female [x 46] E. laphygmae.............................................- 150
Plate 6.20: Schematic diagram of fore-wing and hind-wing of male
E. laphygmae [x 30 ]...................................................................................- 152
Plate 6.21: Schematic diagram of hind leg of E. laphygmae [x 90] ......................... - 153
Plate 6.22: Schematic diagram of antenna of female E. laphygmae [x 100]................- 154
Page
List o f Plates Cont'd.
Plate 6.23: Schematic diagram of antenna of male E. laphygmae [x 100] ................. - 155
Plate 6.24: Male Notanisomorphella sp. [x 21].................................................................• '56
Plate 6.25: Propodaeum and carina [x 29]........................................................................ - 156
Plate 6.26: Schematic diagram of male antenna Notanisomorphella sp. [x 90]......... - 157
Plate 6.27: Female [x 50] and male [x 53] O. sokolowskii.......................................... - 158
Plate 6.28: Schematic diagram of antenna of female [x 82] O. sokolowskii.............. - 159
Plate 6J29: Schematic diagram of antenna of male [x 65] O. sokolowskii................. - 159
Plate 6.30: Schematic diagram of fore-wing of O. sokolowskii [x 40]........................- 160
Plate 6.31: Female Tetrastichus atriclavus s.l. [x 68]..................................................- 161
Plate 6.32 Schematic diagram of antenna of female Tetrastichus
atriclavus s.l [x 8 0 ] ....................................................................................- 162
Plate 6.33: Female Pediobius sp [x 29] and male [x 32] ........................................... - 163
Plate 6.34: Schematic diagram of antenna of female Pediobius sp [x 112]............... - 165
Plate 6.35: Schematic diagram of antenna of male Pediobius sp [x 98].....................- 165
Plate 6.36: Female [x 25] Trichomalopsis sp................................................................- 166
Plate 6.37: Male [x 22] Trichomalopsis sp................................................................... - 166
Plate 6.38 Schematic diagram of antenna of female Trichomalopsis sp. [x 67]....... - 167
Plate 6 .39: Schematic diagram of antenna of male Trichomalopsis sp. [x 72]............- 168
Plate 6.40: Schematic diagram of fore-wing of Trichomalopsis sp. [x 82].................- 169
Plate 6.41: Male [x 25] and female [x 41 ] Aphanogmus reticulatus........................... - 170
Plate 6.42: Male [x 40] A. reticulatus.............................................................................   ] 70
Plate 6.43: Schematic diagram of antenna of male A. reticulatus [x 96]....................- 171
Page
xxi
List o f Plates Cont'd.
Plate 6.44: 
Plate 6.45: 
Plate 6.46:
Schematic diagram of antenna of female A. reticulatus [x 90]
Blepharella sp. nr. vasta [x 3.8]...............................................
Peribaea orbata [x 15].............................................................
CHAPTER ONE
GENERAL INTRODUCTION
The common cabbage, Brassica oleracea L. var. capitata belongs to the family 
Brassicaceae, commonly referred to as the Brassicas. It is a native of the
Mediterranean regions and Southern England, Wales and Northern France (Norman, 
1992). Cabbage is thought to have evolved from a leafy, unbranched, thin-stemmed 
kale, B. oleracea but it is now cultivated throughout the world for its foliage bud 
(Prakash and Rao, 1997). It is a biennial herb with short thickened stem surrounded 
by a mass of overlapping expanding leaves, which form a compact head (Norman, 
1992; Obeng-Ofori el al., 2007). Cabbage is usually grown as an annual crop 
although it is a biennial, which can grow up to 90 cm (Watts and Watts, 1951). When 
left to complete its cycle, the crop will produce a large more or less dense head of 
leaves from a condensed stem in the first year, and then, an appreciable intemode 
elongation will occur in the second year terminating in the formation of inflorescence 
(Norman, 1992). There is a great variation in the cultivated varieties of cabbage. 
They differ in shape, size and colour of leaves and size, and in the shape, colour and 
texture of heads. However, in the common cabbage, the leaves are relatively smooth 
and form a compact head.
Cabbage thrives best in a cool moist climate with temperature of 16-20 °C, but a 
number of varieties available now are well adapted to the tropics (Norman. 1992). 
There is no documented evidence as to when cabbage was introduced into Ghana. It 
is, however, believed to have been cultivated in the country as far back as the 1940's 
by the British (Sinnadurai, 1992). It may be grown throughout the year if irrigation or
other supplementary water is available. It is produced throughout the country, but of 
less importance in the Upper East Region (Timbilla and Nyarko, 2004). It is popular 
in the urban areas of Ghana where it is produced mainly by backyard and market 
gardeners (Ninsin, 1997). In the forest zone, it tends to grow better in the minor rainy 
season, but on the Accra plains, better yields are obtained during the main season. It 
does remarkably well at cooler mountainous areas of the country such as Akwapim 
and Kwahu, and the moist high elevations around Tarkwa in the Western Region 
(Bangnikon. 1996). Cultivars suitable for production in Ghana are Copenhagen 
Market, Drumhead, Suttons Tropical, Japanese Hybrid Cabbage, Golden Acre, 
Suttons Pride of the Market, KK Cross, Oxylus and Marion.
Cabbage is used raw in salads such as coleslaw, or as boiled vegetable. It is also used 
for cooked curries, pickles or sauerkraut. The older leaves discarded during 
harvesting are used as animal feed. Cabbage is fairly low in calories and proteins, but 
it is a good source of many minerals, particularly potassium, and it is relatively high 
in vitamins A, B and C (Norman, 1992). Yield of cabbage in Ghana varies according 
to the cultivar, weather and quantity of fertilizers applied. The average weight of an 
early maturing variety could be 1.5 kilogram per head. Thus, yield can vary from
18,000 kilograms per hectare for an early cultivar to 26,000 kilograms for a late 
cultivar (Obeng-Ofori et al., 2007).
The cultivation of cabbage is threatened worldwide by the various lepidopterous pests 
that attack the crop (Oatman, 1966; Jusoh et. al., 1992; Pratissoli et al., 2008) and 
cause extensive damage to it (Goodwin, 1979; Hamilton et al., 2004). The major ones 
are the diamondback moth Plulella xylostella L., the cabbage looper, Trichoplusia ni
2
(Hubner), the imported cabbage worm, Pieris rapae (L.), the webworm, Hellula 
undalis (F.) and the cabbage head caterpillar, Crocidolomia binotalis Zeller (Smith 
and Brubaker, 1938; Harcourt, 1956; Sastrosiswojo and Sastrodihardjo, 1986; Walunj 
and Pawar, 2004; Obeng-Ofori et al., 2007).
The control of these pests has depended mainly on the use of synthetic insecticides 
which has led to emergence of resistance and adverse effects on natural enemies 
(Verkerk and Wright, 1996; Ninsin, 1997; Dobson et al., 2002). In addition, the 
increasing cost of chemicals (Obeng-Ofori, 2000; Youdeowei, 2002) and the very 
frequent application of cocktails without achieving control (Ooi and Sudderuddin, 
1978; Sarfraz et al., 2005) make alternative pest management strategies, especially 
biological control necessary (Abdel-Razek et al., 2006).
Even though the diamondback moth, Plutella xylostella is considered the primary pest 
on cabbage, data on population trends and seasonal incidence are either lacking or 
poorly documented in many tropical countries (Kuwahara et al., 1995). In Ghana, P. 
xylostella, Trichoplusia ni and Hellula undalis are considered serious pests on 
cabbage (Bangnikon, 1996; Obeng-Ofori and Ankrah, 2002; Obeng-Ofori et al., 
2007). However, there has neither been a systematic study on their seasonal 
incidence nor the occurrence of the other lepidopterous pests. Studies have been 
restricted to pesticide evaluations and a few short-term studies or observations on 
damage and behaviour. Virtually no study has been carried out to determine the 
correct identity, action and importance of the natural enemies of these pests on 
cabbage (Obeng-Ofori et al., 2007). Much of the available literature is on P. 
xylostella and it is from South East Asia, the Americas and Europe (Harcourt et al..
3
1955; Oatman and Platner, 1969; Talekar, 1992; Pratissoli el al., 2008). It is therefore 
imperative that in Ghana, the seasonal incidence of the lepidopterous pests be 
determined, in order to provide a more sustainable basis for their management and to 
contribute to the existing body of knowledge. In this study, more emphasis will 
however, be placed on P. xylostella.
Population studies are important for determining the times of the year when damage is 
caused, the levels of parasitism of the pests of cabbage, appropriate tuning for 
effective use o f insecticides and other control measures (Kuwahara et al., 1995; Liu et 
al., 2000; Mosiane et al., 2003). Generally, most of the field data on the relationships 
between parasitoids and host populations, lack a holistic approach (Guan-Soon, 
1992). There is therefore, an urgent need for an in-depth study on the parasitoids in 
order to appreciate their role and to gain a better understanding of strategies that can 
be used to manipulate local populations (Mahr, 1996; Riba et al., 1996; Pratissoli et 
al., 2008).
The diamondback moth populations’ native to different regions have morphological 
and biological differences, and specific parasitoid strains may be associated with the 
specific diamondback moth strains (Salinas, 1986; Sarfraz et al., 2005). Incorrect 
identification and the difficulty of associating pests with parasitoids have led to 
numerous occasions when biological control has either failed or delayed (Yaninek and 
Herren, 1989; Bio-NET INTERNATIONAL, 1999).
The main objective of this study therefore, was to determine the incidence and
seasonality of the major Lepidopteran pests of cabbage as well as the associated
parasitoids and the levels of parasitism in southern Ghana.
The specific objectives were:
1. To determine the major Lepidopteran pests on cabbage in southern Ghana.
2. To determine the parasitoid-host associations in an annual production of
cabbage and the effect of commonly used insecticides on parasitism and 
development of the dominant parasitoid.
3. To study the biology of the parasitoids with emphasis on the dominant one 
that could be used in an integrated pest management programme.
4. To describe the pests in relation to damage and behaviour on cabbage in
southern Ghana.
5. To describe the parasitoids associated with the pests in southern Ghana.
5
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 Insect Pests of Cabbage
Cabbage, Brassica oleracea var. capitata, is a crucifer of economic value that is 
cultivated worldwide in both the tropics and temperate regions of the world. The crop 
supports a variety of insect fauna (Oatman and Platner, 1969; Talekar, 1992). Its 
successful cultivation is hampered by the incidence of various defoliating caterpillars 
(Srinivasan and Krishna-Moorthy, 1992; Hu et al., 1997; CAB International, 1999). 
The major insect pests are the diamondback moth, Plulella xylostella, the cabbage 
looper, Trichoplusia ni, the imported cabbage worm, Pieris rapae, the webworm, 
Hellula undalis, the variegated grasshopper, Zonocerus variegatus, and the cabbage 
head caterpillar, Crocidolomia binotalis (Harcourt, 1956; Youdeowei, 2002; Obeng- 
Ofori et al., 2007; Pratissoli et al., 2008). Other pests recorded on cabbage include 
the com earworm Helicoverpa armigera (Hubner), the African army worm, 
Spodoptera exempt a (Walker), cabbage maggot Hylemya brassica (Bouche), cabbage 
flea beetles Phyllotreta cruciferae (Goeze), and cabbage aphids Brevicoryne 
brassicae (L.). One or more of these are considered occasional or seasonal pests in 
various countries (Boling and Pitre, 1971; Waterhouse, 1992; Poelking, 1992; Berg 
and Cock, 2000).
Plulella xylostella is considered the most destructive and occurs worldwide wherever 
cabbage and other crucifers are grown (Tadashi et al., 1986; Pratissoli et al.. 2008). 
Attack by P. xylostella can lead to total destruction of the crop at all stages of plant
6
growth, and the production of unmarketable heads (Sachan and Srivastava, 1972; 
Loke et al.. 1992; Syed, 1992; Sivapragasam and Abdul Aziz, 1992).
The 1999 Annual Report of WE1CO, a vegetable growing and irrigation company in 
Ghana and Obeng-Ofori el al. (2007) indicate that the diamondback moth is a serious 
pest in various parts of Ghana. Sometimes the crop is harvested prematurely or 
abandoned due to diamondback moth infestation (Cobblah, 2000).
Up to 1972, at least 128 countries or territories had reported the occurrence of P. 
xylostella (CAB International, 1999). It has been estimated that one billion US 
dollars is spent annually on its control worldwide in addition to the crop losses it 
causes (Talekar and Shelton, 1993; Vasquez, et al., 1997; Abdel-Razek et a l, 2006).
The level of infestation of P. xylostella varies considerably (Harcourt el al., 1955; 
Dennill and Pretorius, 1995). It is serious in S. E. Asia (Talekar et al., 1992) and 
moderately so in parts of Canada and USA (Hardy 1938; Sutherland, 1966; Oatman 
and Plainer 1969; Hill and Foster, 2000). In Germany and France, it is not present in 
sufficient numbers to be considered a serious pest (Lim, 1986) whilst in South Africa, 
it is ranked substantially low (Bell and McGeoch 1996; Kfir, 1997; Mosiane et al..
2003). A study by Weires and Chiang (1973), found the diamondback moth to be 
dominant in only three locations while Hellula undalis, Plusia orichalcea (Hubner). 
Agrotis ipsilon (Hufnagel), Helicoverpa armigera, Crocidolomia binotalis and 
Spodoplera sp. were dominant in four locations (cited from Sastrodihardjo. 1986). 
Even though Koshihara (1986) recognised the diamondback moth as an important 
pest in Japan, the author observed that, prior to head formation, the imported cabbage
7
worm, Pieris rapae and the cabbage armyworm Mamestra brassicae (L.) could cause 
heavier visual leaf damage.
Hellula undalis is a major pest on cabbage seedlings in nurseries as well as 
transplanted young plants in the field in Guam (Muniappan and Marutani, 1992). It is 
of growing concern in the lowlands of Malaysia warranting serious attention 
(Sivapragasam and Abdul Azziz, 1992). However, Ooi (1979a) considered it as a 
minor pest in low altitudes with cooler temperatures as was observed in India (Sachan 
and Gangawar. 1980). In Hawaii, Jayma and Ronald (2007) observed that 
comparatively, the pest is not of great significance. Obeng-Ofori and Ankrah (2002) 
noted that H. undalis is a serious pest of cabbage in Ghana.
Trichoplusia ni is considered a serious pest in many parts of the USA and Canada 
(Chalfant, 1992; Wyman, 1992; Capinera, 1999) overshadowing the diamondback 
moth because of its voracious feeding habits (Hill and Foster, 2000). In Thailand it is 
considered as a minor pest, though potentially very damaging to young plants from 
seedling to bolting (Rowell et al, 1992). The authors added that it appears to cause 
little damage after this stage. In Nigeria, the pest can reach epidemic levels on 
cabbage when not controlled (Anene and Dike, 1996). In Ghana, T. ni can cause 
considerable damage to the cabbage leaves and heart (Obeng-Ofori and Ankrah. 
2002).
Crocidolomia binotalis, though a secondary pest of cabbage in Indonesia, can be a 
serious problem in the dry season (Sastrosiswojo and Setiawati, 1992) and is 
important at certain times of the year in Malaysia where it occurs with the
8
diamondback moth (Kadir, 1992). Various species of armyworms such as Spodoptera 
exigua (Hubner) may be serious pests on cabbage in parts of S. E. Asia (Wakamura 
and Takai. 1992) but S. littura (F.) is seasonal in other countries (Muniappan and 
Marutani. 1992).
A list of major pests of cabbage worldwide is presented in Table 2.1.
Table 2.1 Major Pests of Cabbage and Damage Worldwide
Name of species Order/Family Damage & Part Attacked
Plulella xylostella (L.) Lepidoptera/Plutellidae Larvae feed on leaves
Pieris rapae (L.) Lepidoptera/Pieridae Larvae defoliate leaves
Pieris canidia (L.) Lepidoptera/Pieridae Larvae defoliate leaves
Hellula undalis (F.) Lepidoptera/Pyralidae Larvae eat growing points
Agrotis ipsilon (Hufnagel) Lepidoptera/Noctuidae Larvae are cutworms
Agrotissegetum (Schiffermuller) Lepidoptera/Noctuidae Larvae are cut worms
Brevicoryne brassicae (L.) Hemiptera/Aphididae Larvae Infest foliage
Lipaphis erysimi (Kaltenbach) Hemiptera/Aphididae Larvae infest foliage
Aleyrodes brassicae (L.) Hemiptera/AIeyrodidae Larvae infest foliage
Delia brassicae (Bouche) Diptera/Anthomyiidae) Larvae eat roots
Aulacophora similis (Olivier) Coleoptera/Chrysomelidae Adults chew leaves
Phyllolreta spp Coleoptera/Chrysomel idae Adults chew leaves
Leucopholis irroraia (Chevrolat) Coleoptera/Scarabaeidae Larvae chew roots
Trichoplusia ni (Hubner) Lepidoptera/Noctuidae Larvae defoliate plant
Zonocerus variegalus (L.) Orthoptera/Acrididae Chew leaves in nursery
Sources: Hill, 19H3; Youdeowei. 2002; Obeng-Ofori and Ankrah, 2002
9
2.2 Origin and Distribution of the Pests
The most probable origin of the diamondback moth has been postulated to be the 
Mediterranean region (Hardy, 1938). This is based on circumstantial evidence that 
the largest contiguous area of its distribution is Europe, where the Brassicas had been 
cultivated since ancient times (Strasburger, 1921, cited in Hardy, 1938). The complex 
of natural enemies present there and the effective natural control reported lend support 
to this assertion (Ooi, 1986). It is likely that the diamondback moth was spread along 
with the spread o f Brassicas from their original home. Kfir (1997) proposed that 
Plutella xylostella may have originated from South Africa. In addition to its effective 
control and the rich fauna of parasitoids which had been used as the basis for its 
European origin, the author argued that the lower pest status of the diamondback moth 
in South Africa compared with other countries with similar climates, the large number 
of indigenous Brassicas and parasitoids are more compelling reasons. However, Liu et 
al. (2000 ) indicated that the data from their study seem to add confusion to such 
speculations because most of the arguments used by Kfir (1997) seem to apply to 
China.
Only a few agricultural pests are as cosmopolitan as the diamondback moth and they 
have been recorded beyond latitude 60°N in Iceland in the temperate region and in the 
tropics (Ooi, 1986). It has the ability to survive a wide range of temperatures both in 
the tropic and temperate regions (Salinas, 1986). The pest is completely cosmopolitan 
in distribution, extending northwards up to the Arctic Circle (Frost, 1949; Hill, 1983) 
and to the Tropics (Talekar, 1992).
10
Trichoplusia ni is very widely distributed throughout the tropics and sub-tropics, with 
the exception of Australasia, and extends up into the warmer parts of southern Canada 
and Europe (Hill, 1983). It is found wherever crucifers are grown. It is highly 
dispersive and adults have sometimes been found at high altitudes and far from shore. 
Flight ranges of approximately 200 km. have been estimated (Capinera, 1999).
Hellula undalis was first identified in Italy but has now spread throughout the Middle 
East, Asia, North and West Africa, parts of Australia and to the Pacific islands (Hill, 
1983; Muniappan and Marutani; 1992; Jayma and Ronald, 2007).
Description of the Pests
General descriptions of the developmental stages of the diamondback moth have been 
given by various workers (Hardy, 1938; Harcourt, 1956; Moriuti, 1986). However, 
the diamondback moth populations native to different regions have genetic and 
biological differences and the behavioural and morphological parameters of the 
developmental stages also vary (Salinas, 1972; Sarfraz et al., 2005).
The adult is a small, slender, greyish-brown insect measuring 11-16 mm long with a 
wing span of about 10 mm (Hardy, 1938; Harcourt, 1956). It is also described as a 
greyish moth with a wing expanse of 14 mm, the male having an expanse of 12.97 
mm and the female 13.0 mm (Chelliah and Srinivasan, 1986). The common name of 
the diamondback moth is based on the fact that, when at rest, the wings are closely 
applied to the sides of the body meeting above and presenting a slightly upturned 
diamond appearance at the rear end. Although colour variations occur, the females 
are generally lighter than the males (Harcourt, 1956; Moriuti, 1986).
The egg of the diamondback moth is described as yellowish white to yellowish green, 
cylindrical to oblong in shape, and measuring 0.48 nun by 0.25 mm (Bhalla and 
Dubey, 1986). It has also been described as whitish yellow with a length of 0.5 mm 
(Chelliah and Srinivasan, 1986). The larva may be whitish yellow to pale green or 
pale white with a pale brown head when freshly hatched (Chelliah and Srinivasan, 
1986). The authors described the fully grown larva as light green, moderately stout, 
smooth, with short scattered hairs and varying in length from 8.62 to 10 mm. The 
pupa is light brown with a mean length of 5.15 - 7 mm (Harcourt, 1956; Bhalla and 
Dubey, 1986).
The adult of Trichoplusia ni is a dark brownish moth with a wing span of about 35mm 
(Hill, 1983). The fore wings are mottled grey-brown in colour and the hind wings are 
light brown at the base, with the distal portions dark brown (Capinera, 1999). The 
forewing bears silvery white spots centrally: a U-shaped mark and a circle or dots that 
are often joined or resemble a figure ‘8 ’ (Hill, 1983; Capinera, 1999).
The egg of T. ni is hemispherical in shape, with the flat side affixed to foliage 
(Capinera, 1999). The author described it as yellowish white or greenish in colour, 
bears longitudinal ridges and measures about 0.6 mm in diameter and 0.4 mm in 
height The larva is basically green in colour, with a thin, white, lateral line and two 
white lines along the dorsal surface (Hill, 1983). The larva has three pairs of prolegs 
and move by arching its back to form a loop and then projecting the anterior section 
of the body forward. The thoracic legs and head are usually pale green and the 
mature larva measures about 3 - 4cm long (Capinera, 1999). The newly formed pupa
12
is green, but later turns dark brown or black. It measures about 2 cm in length 
(Capinera, 1999).
The developmental stages of the cabbage webworm, Hellula undalis have been 
described by (Jayma and Ronald, 2007). The authors described the adult as a greyish- 
brown moth with a wing span of about 2 cm. The forewings have wavy grey 
markings, a curved pale patch subterminally and a kidney shaped mark about one 
third way towards the tip. The eggs of the cabbage webworm are ovoid in shape and 
about 0.52 mm long. The surface attached to the foliage is slightly flattened. When 
freshly laid, it is pearly white but becomes pinkish after a day and then turns brownish 
red, just before hatching (Hrakly, 1968a; cited in Jayma et al., 2007). The larvae are 
greyish - yellow with five broad, irregular reddish-brown bands that extend the length 
of the body. The pupae are about 12 mm long. The newly formed pupa is soft and 
pale yellowish, but becomes hard and light brown within a few hours.
Life History of the Pests
The life histoiy and other aspects of the biology of the diamondback moth, Plutella 
xylostella have been documented by various workers (Harcourt, 1960a & b; Talekar 
and Griggs, 1986; Talekar, 1992). In general, an increase in temperature leads to a 
shortening of the developmental time of all stages up to a certain optimum depending 
on the area (Bhalla and Dubey, 1986; Salinas, 1986). In tropical conditions where 
temperatures range from 28-31  °C, the life cycle is completed within 14 - 24  days 
(Alam, 1992). 14-21 days have been reported by Harcourt (1957) in Canada, 10.8 - 
27 days in Malaysia by (Ho, 1965) and 25.3 - 27.2 days in northern India by Yadav et 
al. (1974). Even in the same region, Ko and Fang (1979) reported only 9 days for a
single generation under favourable conditions while, in winter, one generation took 
110  days.
The eggs are laid singly or in batches of up to four under the leaves (Bhalla and 
Dubey, 1986). Incubation period varies between 3 - 8  days and larval periods range 
from 6-17.5 days (Harcourt, 1957; Salinas, 1986). Four larval instars were recorded 
by Harcourt (1956) and Jayarathnam (1977), whilst Patil and Pokharkar (1971) 
recorded five instars. The fully grown larva spins an open net silken cocoon which is 
open at both ends, or a loose mesh of silken cocoon and pupates inside it on the leaf 
(Chelliah and Srinivasan 1986; Ooi, 1986). The pupal period is reported to vary from 
4 - 1 5  days depending upon the temperature (Abraham and Padmanabhan, 1968; 
Salinas, 1986).
The adults are most active at dusk from 6.30 - 7.30 pm at temperatures of 20 - 21 °C 
and 90 - 95% relative humidity at which they mate and oviposit (Frost, 1949; 
Poe Iking, 1992). Longevity of the adults varies from location to location. Harcourt 
(1957) gave a range of 3 - 58 days for males and 7 - 4 7  for females whilst Salinas 
(1986) gave 8 - 1 6  days for females in the presence o f the host plant, and 11-27 days 
in the absence of the host plant
The life history of the cabbage looper, Trichoplusia ni has been studied by Hill (1983) 
and Capinera (2008). They observed that the number of generations completed per 
year overlap and varies from 2 to 5 depending upon the temperature. The total 
developmental period may take between 1 8 - 2 5  days at 32 - 21 °C respectively
14
(Capinera, 1999). The lower limit for development is about 10 - 12 °C and 40 °C is 
fatal to some stages.
The eggs of Trichoplusia ni are deposited singly on either the lower or upper surface 
of the leaf, although clusters of six to seven eggs are not uncommon (Capinera, 1999). 
The incubation period of the egg varies from 2 - 1 0  days and larval periods range 
from 20 - 35  days depending upon the temperature. Hill (1999) recorded five larval 
instars but, Capinera (2008) recorded four to seven instars. Pupation takes place in a 
white, thin, fragile cocoon formed on the underside of foliage, in plant debris, or 
among clods of soil. Capinera (1999) reported that the pupal period of T. ni takes 4 - 
13 days depending upon the temperature.
The adults of Trichoplusia ni are considered to be semi-noctumal because feeding and 
oviposition sometimes occurs around dusk (Capinera, 1999). Flight ceases at about 
16 °C but activity is higher on warmer evenings (Hill, 1963; Capinera, 2008). The 
female oviposits readily at temperatures as low as 15.6 °C and may lay 300 -  600 eggs 
in her life time (Shorey, 1963).
The life history of the cabbage webworm, Hellula undalis was studied by Jayma and 
Ronald (2007) in Hawaii. They observed that the upper and lower threshold for 
development is about 36.6 °C and 20 °C respectively, and that the complete life cycle 
varies from 17-52 days.
The eggs are laid singly, or in groups of two or three on the leaves of cabbage near the 
bud. Incubation period of the egg varies from 2 - 3 days at a mean temperature of
15
27.8 °C (Awai, 1958; cited in Jayma and Ronald, 2007; Sivapragasam and Abdul 
Aziz, 1992). There are five larval stages which are completed in 14 days at 28 °C. 
Pupation occurs in a silken cocoon either in a tunnel constructed at the entrance of the 
feeding tunnel, between leaves, inside the stem and bases of dropped leaves or deep in 
the soil surrounding the plant. Pupal period lasts 8 days at 27.8 °C (Sivapragasam and 
Abdul Aziz. 1992).
The adults of Hellula undalis live for 4 to 8 days depending upon the temperature. 
Oviposition begins within 24 hours of emergence and continues for 3 to 10 days 
(Sivapragasam and Abdul Aziz, 1992).
Host Range of the Pests
The diamondback moth is an oligophagous insect that feeds on plants that contain 
mustard glucosides (Thorsteinson, 1953; Gupta and Thomsteinson, 1960). The 
cruciferous plants are an important economic group of plants with mustard glucosides. 
thus, wherever they are found, the diamondback moth is present (Ooi, 1986). In some 
cases, it is restricted to introduced or cultivated species of Brassica (Salinas, 1986). 
Being a crucifer specialist, it has adapted to the unique secondary chemistry of this 
family of plants that is toxic to most generalist feeders (Verkerk and Wright, 1996).
The diamondback moth has been observed as a major pest on Brussels sprouts in 
Canada (Butts and McEwen, 1981), radish, Raphanus sativus (L.) and watercress. 
Nasturtium officinale (Hill, 1983). Other host plants include collards (Brassica 
oleracea var acephala (L.), Chinese cabbage, B. campestris L. subspecies pekinensis 
(Lour) Olsson, (Talekar and Yang, 1991), Broccoli, Brassica oleracea (L.) var
botrytis (Zhao et al, 1992; Mitchell et al., 1997a; Martinez-Castillo et al., 2002). 
Mosiane et al. (2003) reported that in South Africa, canola, Brassica napus (L.) is a 
major host plant of the diamondback moth. In Ghana, it is associated with the 
cauliflower, B. oleracea var botrytis (L.), B. oleracea var capitata (L.) and B. 
campestris L. subspecies pekinensis (Obeng-Ofori et al., 2007). Kmec and Weiss 
(1997) reported that this pest also occurred on the crop, crambe, Crambe abyssinica 
Hochst and the weed, field pennycress, Thlapsi arvense L. Other alternative hosts 
consist of a wide range of wild cruciferous plants (Hill, 1983). It had also been 
recorded on the non-crucifer, Amaranthus virdis L (Vishakantaiah and Visweswara 
Gowda. 1975) and on okra, Abelmoschus esculentum (L.) Moench (Gupta, 1991; 
Cobblah, 2000).
The cabbage looper, Trichoplusia ni feeds on a variety o f crucifers and other 
cultivated plants and weeds. It has been reported damaging Brassica oleracea var 
capitata, B. oleracea var. acephala, B. campestris subspecies pekinensis, Brassica 
oleracea var botrytis in Canada and the United States of America (Harcourt. 1963; 
Capinera, 1999). It has also been recorded on cotton, tomatoes, legumes, sweet potato 
and water melon (Hill, 1983; Capinera, 1999). Capinera (1999) also noted that 
additional hosts are flower crops such as chrysanthemum, snapdragon and sweet pea 
and agricultural weeds such as wild lettuce, Lactuca spp.; dandelion. Taraxacum 
officinale; and curly dock, Rumex crispus. In Ghana, it is associated with the 
cauliflower, B. oleracea var botrytis and B. oleracea var capitata (Obeng-Ofori et al..
2007).
Hellula undalis is host specific to cruciferous crops in Guam and it is associated with 
Chinese cabbage, Brassica pekinensis, green mustard, B. juncea and the common 
cabbage, B. oleraceae (Muniappan and Marutani, 1992). In Thailand, Australia, 
North and West Africa, and Hawaii it is recorded on various crucifer crops (Hill, 
1983; Rowell, et al., 2005; Jayman and Ronald, 2007). Obeng-Ofori et al. (2007) 
observed that in Ghana, H. undalis is associated with the common cabbage and 
cauliflower.
Damage by the Pests to Cabbage
The diamondback moth is the primary pest of cabbage worldwide and all the 
developmental stages occur on the plant The behaviour and feeding damage caused 
by the pest have been described by (Talekar and Griggs, 1986; Talekar, 1992; Obeng- 
Ofori et al. 2007). Its behaviour on the plant appears to be similar world-wide 
(Hardy, 1938; Harcourt, 1957; Sastrodihardjo, 1986). The newly hatched larva is 
essentially a leaf miner, forming shallow mines on the underside of the leaf and 
feeding in the spongy mesophyll (Dobson et al., 2002). These show up as numerous 
white markings on the leaves. Hardy (1938) contended that this behaviour is not 
obligatory but, it is an adaptation enabling the young larva to consume as much 
parenchyma without the necessity of chewing through much of the toughened 
epidermis with its comparatively weak mandibles. When provided with tender thin 
leaves they do not mine but behave as surface feeders.
The subsequent instars are surface feeders, usually on the underside of the leaves. 
They chew all the leaf tissues with the exception of the veins and the upper epidermis, 
causing irregular transparent areas or patches on the leaves. This “windowing” effect
is distinctive of P. xylostella damage. The attack may begin from the seedling stage 
to maturity but there is a preference for the central leaves of young plants (Koshihara, 
1986). They may also feed on the outer leaves. These feeding activities retard 
vegetative growth, render the heads unmarketable, and may lead to total destruction of 
the crop. When disturbed, even slightly, the larvae wriggle backwards or drop down 
unto the lower leaves by suspending themselves on a silken thread.
The larvae of the cabbage looper, Trichoplusia ni are leaf feeders and cause 
considerable damage to cabbage. The first three instars confine their feeding to the 
lower leaf surface leaving the upper surface intact (Capinera, 1999). The author also 
observed that the fourth and fifth instars chew large holes in the leaf, and feed on the 
wrapper leaves as well as the developing head. Obeng-Ofori et al. (2007) noted that 
the larvae bore irregular holes in the leaf lamina and attack the newly formed heads 
resulting in numerous feeding punctures that are filled with frass. Even though, the 
larvae are voracious and consume three times their weight in plant material daily, they 
are not always destructive (Capinera, 1999). In Thailand, Trichoplusia ni can be 
potentially damaging to young plants from the seedling stage until bolting, but 
appears to cause little damage to the seed crop thereafter (Rowell, et al.. 1992). On 
the other hand, Prasad (1963) observed that T. ni reduced yield of marketable crop by 
64 - 78%. In the United States of America, moderate defoliation prior to head 
formation is irrelevant, but average population densities of 0.3 larvae per plant justify 
control (Kirby and Slosser, 1984; cited in Capinera, 1999).
The larvae of Hellula undalis cause damage to the terminal shoots and midribs of 
leaves, and in severe cases, such damage result in the development of multiple heads.
19
which are small and unmarketable (Muniappan and Marutani, 1992). It may cause 
occasional damage to young plants in the pre-flowering stage (Rowell, et al., 1992). 
Sivapragasam and Abdul Azziz (1992) observed that damage is most severe between 
transplanting and the heading stage of cabbage, even though, the larvae are present in 
the field throughout the crop. Severe damage or death occurs when the larvae tunnel 
into the main stem (Jayma and Ronald, 2007). In Ghana, Obeng-Ofori and Ankrah 
(2002) reported that the larvae of H. undalis attack the leaves, stalk and heart of 
cabbage, and also spin together the leaves with silken thread.
2.7 Seasonal Incidence of the Pests
Incidence and population trends vary for the various lepidopterous pests on cabbage. 
Seasonal incidence of the diamondback moth in relation to various factors has been 
described (Harcourt, 1957; Sachan and Srivastava, 1972; Butts and McEwen, 1981). 
In general, dry and warm weather triggers outbreaks (Sastrodihardjo, 1986) or favours 
population build up (Frost, 1949; Oatman and Platner, 1969; Alam, 1992). Similar 
trends have been found in India (Abraham and Padmanabhan, 1968; Yadav et al.. 
1974). In India, Rustapakomchai and Vattanatangum (1986) also recorded high 
build-up of the larvae in the summer, dry season and the mid-rainy season whereas 
Nagarkatti and Jayanth (1982) recorded significantly higher build-up during the rainy 
season, compared with other seasons.
Observations by several workers indicate that temperature is a limiting factor in the 
population dynamics of the diamondback moth. A high temperature of 33 °C led to 
low survival rates as it adversely affected the development and emergence rates 
(Wakisaka et al., 1992). Dennili and Pretorius (1995) reported 10.5 °C and 25.8 °C as
20
being within the critical limit. Koshihara (1986) reported a daily minimum range of 5 
- 12 °C and a maximum of 21 - 36 °C as favourable for multiplication of the 
diamondback moth. The diamondback moth may occur all year round (Harcourt, 
1963) and even in winter at a minimum temperature of 10 °C, but the population 
densities differ (Koshihara, 1986). The number of generations is higher in the hot 
lowlands than in the highlands of Thailand and survival rates are higher in the hot dry 
season than in the wet season (Keinmeesuke et al., 1992). Humidity has little 
influence on the development and survival, as the immature stages live in specialised 
microclimate (Hardy, 1938).
The population of the diamondback moth is high early in the cropping season 
(Harcourt, 1986), peaking at 45 days after transplanting (Sastrodihardjo, 1986; Rowell 
et al., 1992), or before cupping (Chalfant et al., 1979; Dennill and Pretorius, 1995; 
Mosiane et al., 2003) and declining thereafter. The diamondback moth is a 
multivoltine species and several generations overlap in a single crop or annually, 
making it very difficult to study its life cycle in the field. In warm parts of Japan and 
South East Asia, up to 15 and 20 generations overlap annually (Talekar and Griggs, 
1986; Poelking, 1992).
The incidence of attack and population densities vary widely within plants and even 
within fields in the same growing season (Harcourt, 1960a, 1961; Hu et al., 1997). In 
certain areas of South Africa, 11.6 larvae per plant was observed by Ullyet (1947) 
while Denill and Pretorious (1995) recorded 0.42 larva per plant Peaks of 1.6 to 3.6 
larvae/plant in four seasons were reported by Oatman and Plainer (1949) with pupae 
following the same trend. Densities of 2.5 - 20 larvae per plant had been recorded by
21
several workers in different areas (Prasad, 1963; Baker et al., 1982; Simonet and 
Murisak, 1982; Andaloro et al., 1982). High densities of 477 larvae/plant in an 
outbreak period and mean population densities of 2 to 78 larvae/plant, with a 
maximum of 160 larvae/plant, were reported by Wan (1970) and Ooi (1979a & b), 
respectively. Harcourt, et al. (1955) observed a mean population build up of 14.9 to
26.9 larvae/plant by the end of harvest. The infestation of cabbage by the 
diamondback moth varied from 5% to 100% in the growing season whilst between 
3% and 73% of plants were infested with larval populations ranging between 3 and 
415 per 100 plants (Prasad, 1963; Sachan and Srivastava, 1972).
Weeds have been shown to maintain Plutella xylostella populations during the off­
season periods. Kmec and Weiss (1997) observed that, peak populations occurred 
first on weeds before the moths move onto the cultivated crop. Larval densities were 
higher on rows adjacent to weeds and bushes than in the interior of fields but these 
varied among fields (Hu et al., 1997).
With regard to Trichoplusia ni, temperature has been found to be a limiting factor in 
its incidence and activity. Hill (1983) observed that in temperate areas the larvae 
continue to be active at low temperatures; generally flight ceases at about 16 °C and 
larval development at about 12 °C. In warm regions however, there may be 5 
generations per year or more as a result of continuous breeding. Overwintering of the 
pest apparently occurs only in the southernmost states of the USA; it is erratic in 
occurrence, typically very abundant in one year, and then scarce for two to three years 
(Capinera, 1999). The author also noted that, the number of generations per year 
overlap and varies from two to seven. In Nigeria, Anene and Dike (1996) observed
22
that populations were high during the rainy season and could reach epidemic levels. 
On the other hand, Hofmaster (1961) cited in Capinera (1999) reported that cabbage 
looper populations in Virginia were highest during dry weather because rainfall 
assisted the spread of Nuclear Polyhedrosis Virus (NPV), which greatly suppressed 
the population. In India, populations of T. ni reach their peak by early September and 
remain high till the last week, and then declines greatly up to February. During the 
peak period 32% of plants are infested (Sachan and Srivastava, 1972). Wyman 
(1992) noted that in Central North America, populations were high in all fields in mid 
to late season. Chalfant et al. (1997) also reported that populations of the pest were 
heaviest after cupping until harvest.
The adults o f Hellula undalis are primarily active at night (Jayma and Ronald, 2007). 
Populations reach their peak by about middle of August, declines during October, and 
it is negligible in winter in India (Sachan and Srivastava, 1972). Wyman (1992) noted 
that in Central North America H. undalis occurs in small numbers sporadically 
throughout season.
2.8 Mortality Factors Influencing the Survival of the Pests
2.8.1 PluteUa xylostella
Factors affecting the abundance of the diamondback moth have been studied by a 
number of workers (Hardy, 1938; Harcourt, 1963; Kmec and Weiss, 1997). The 
major mortality factors are parasitoids and rainfall (Harcourt 1963; Lim, 1986; 
Keinmeesuke et al, 1992; Capinera, 2005). However, Hardy (1938) suggested that 
rainfall may be important only at certain critical periods in the life cycle and argued 
that temperature was more critical.
23
2.8.1.1 Rainfall
The effect of rainfall is manifested by washing away and/or drowning of early instar 
larvae and eggs (Wakisaka et al., 1992; Capinera, 2005) and causing mortality of 
gravid females (Harcourt, 1963; Talekar et al., 1986). Harcourt (1963) found a 
positive correlation between intensity of rain and mortality of the diamondback moth, 
while Rowell et al. (1992) observed low diamondback moth populations after the 
rains.
2.8.1.2 Parasitoids
All the developmental stages of the diamondback moth are attacked by parasitoids. 
Only a few species have been reared from the eggs and they belong to the genera 
Trichogramma and Trichogrammatoidea. These however, contribute little to 
mortalities in the diamondback moth (Yamada and Yamaguchi, 1985; Waterhouse. 
1992; Alam, 1992). The greatest control is provided by the endo-larval parasitoids 
(Ooi, 1970; Talekar, 1992; Liu et al., 2000; Mustata et al., 2006). The main larval 
parasitoid species that are reported to cause significant mortalities belong to the 
Hymenoptera genera, Diadegma Foerster (Ichneumonidae), Microplitis Foerster and 
Cotesia Cameron Braconidae) (Waterhouse and Norris, 1987; Waladde et al., 1997; 
Rowell et al., 2005). Even though, the importance of the different genera varies from 
place to place (Mustata, 1992), several accounts on parasitism of the diamondback 
moth indicate that, of the three genera, Diadegma species are superior to the others 
(Putnam, 1968; Sastrosiswojo and Sastrodihardjo, 1986; Talekar et al., 1992). As a 
result of this observed superiority, Diadegma species have been introduced into 
several countries, sometimes to augment the impact of other species of the genus
24
Cotesia or some other indigenous species (CIBC, 1977; Ooi and Chua, 1986; Lim, 
1986).
The degree of parasitism varies from species to species and from country to country, 
or even from locality to locality in the same area (Hardy, 1938; Ooi, 1992; Talekar et 
al., 1992; Mustata, 1992). Some species can be effective under specific conditions 
and yet ineffective under other conditions even in the same field or year (Salinas, 
1986).
The three most important species of Diadegma are D. (Angila) eucerophaga Horstm.
D. insulare (Cress) and D. semiclausum (Hellen) (Sastrodihardjo and Sastrosiswojo, 
1986; Ooi and Chua, 1986 and Alam, 1992). A number of reports exist on the 
widespread occurrence of Cotesia (Apanteles) plutellae Kurdjumov in many countries 
(Chiu and Chien, 1972; Ooi, 1979b&c; Loke et al., 1992; Ingham and Kfir, 1997). 
However, in Indonesia and Central America, it is not common (Waterhouse, 1992; 
Andrews et al, 1992.). Reports and observations from laboratory studies regarding 
the superiority of D. semiclausum over C. plutellae contradict some field and 
laboratory observations. Despite D. semiclausum being intrinsically superior to C. 
plutellae, the latter is more dominant in field studies (Ooi, 1992).
Hyperparasitoids broadly defined as parasitoids that seek parasitized hosts and lay 
their eggs into the host or into the developing parasitoid within the host (Greathead et 
al., 1992) have been suggested as contributing to the apparent ineffectiveness of C. 
plutellae and its inability to establish in the field (Ooi, 1979a; Lim, 1982; Alam, 1992; 
Morallo-Rejesus and Sayaboc, 1992). Ooi (1979c & d) reared eight hyperparasitoids
25
from field collected cocoons of C. plutellae and observed hyperparasitism levels of 
between 11.7 - 26.6% whilst Lim (1982) recorded an average of 21%. High 
hyperparasitism rates of 56% (Alam, 1992) and 80% - 90% (Poelking, 1992) by 
Spilochalcis sp. on C. plutellae have also been recorded. Ten different species of 
hyperparasitoids belonging to nine genera had been reared from C. plutellae by 
Chelliah and Srinivasan (1986), Liu et al. (2000), and Mosiane, et al. (2003). Of 
these, the important ones were Aphanogmus fijiensis Ferriere (Ceraphronidae), 
Hockeria atra Masi (Chalcididae), Pediobius imbreus Walker (Chalcididae), 
Pteromalus sp. (Pteromalidae), Tetrastichus sp. (misre group) (Tetrastichidae), 
Brachymeria excarinata (Gahan) (Chalcididae), and Tetrastichus sokolowskii 
Kurdjumov (=Oomyzus sokolowskii), with the last two acting as facultative 
hyperparasitoids. They also found the lowest hyperparasitism level o f 3 - 13% and 
the highest of 39.13%. This high level of hyperparasitism coincided with peak 
parasitism by C. plutellae on the diamondback moth. Morallo-Rejesus and Sayaboc 
(1992) recorded Trichomalopsis sp. as an important hyperparasitoid reducing the 
efficiency of C. plutellae. The negative effect of hyperparasitoids has, however, been 
disputed by other workers who noted that their effects are of little significance 
(Robertson, 1939), and of no economic impact (Mustata, 1992; Mustata et al., 2006). 
The commonest pupal parasitoids belong to the Ichneumonid genus Thyraella 
(-Diadromus), and the Eulophids Tetrastichus Halida^ and Oomvzus Rondani. The 
only one with potential for biological control of the diamondback moth is the 
facultative hyperparasitoid Oomyzus sokolowskii Kurdjumov (Fitton and Walker. 
1992; Liu et al., 2000). It is a gregarious larval-pupal parasitoid exhibiting a density 
independent relationship with the diamondback moth (Ooi and Chua, 1986; Alam.
26
1992). However, T. ayarri (Ollifl) was regarded as a common parasitoid of the 
diamondback moth in S. E. Asia (Ooi, 1986; Fitton and Walker, 1992).
2.8.2 Trichoplusia ni
The cabbage looper Trichoplusia ni is attacked by numerous natural enemies, and the 
effectiveness of each seems to vary greatly. Wasp and tachinid parasitoids, and a 
nuclear polyhedrosis virus (NPV) have particularly been noted to be effective 
(Capinera, 2008). The author noted that predation on the pest has however, not been 
well studied.
2.8.2.1 Parasitoids
Egg parasitism by Trichogramma sp., though variable, could reach about 35% in 
California (Oatman and Platner, 1969). Hill (1983) reported that high field mortality 
of Trichoplusia ni can sometimes be attributed to parasitoids. Larval parasitism has 
been found to average 38.9% with the tachinid Voria ntralis (Fallen) being the 
dominant species in autumn and winter months (Capinera, 2008). Even though, a 
total of twenty four parasitoid species were observed, the authors concluded that they 
are not key factor affecting populations.
2.8.2.2 Nuclear Polyhedrosis Virus
The Trichoplusia ni NVP is reported to be the key factor affecting populations of the 
pest in California (Oatman and Platner, 1969). However, Sutherland (1966) observed 
that in New York, although T. ni NVP is an important mortality factor, natural 
incidence does not appear to be adequate to protect the crop from damage. The erratic
27
occurrence and abundance of the pest in parts of the USA has been attributed to the 
nuclear polyhedrosis virus which is spread by rain (Capinera, 1999).
2.83 Hellula undalis
Very little is known regarding the mortality factors that influence populations of the 
cabbage webworm. In Hawaii, Zimmerman (1958) cited in Jayma and Ronald (2007) 
reported that Chelonus blackburni Cameron is an egg - pupal parasitoid of the pest 
However, its importance in managing webworm population densities is unknown.
2.9 Control Measures Against the Pests
Several control measures have been applied against the major Lepidopteran pests of 
cabbage, especially the diamondback moth in many countries. Simonet and Morisak 
(1982) observed that several factors have to be considered in a pest management 
programme for cabbage feeding caterpillars. Capinera (1999) and Jayma and Roanld 
(2007) on the hand proposed that management strategies should include consideration 
of the complex of crucifer-feeding caterpillars. The control measures include the use 
of various insecticides, biological control, resistant varieties, pheromones, cultural 
and physical methods or combinations of these.
2.9.1 Chemical Control
In many countries, attempts to control P. xylostella have been by the use of synthetic 
insecticides (Chelliah and Srinivasan, 1986; Wyman, 1992). These include relatively 
new chemicals such as avermectins, neonicotinoids and insect growth regulators 
(Abdel-Razek et al, 2006), microbial insecticides such as Bacillus thuringiensis 
Berliner (Bt) (Mahar et al., 2004; Abdel-Razek et al., 2006) and plant based products
28
such as neem, Azadirachta indica A. Juss (Verkerk and Wright 1996; Rowell et al, 
2005; Condor 2007).
In Ghana, the main synthetic insecticide used is lambda cyhalothrin formulated as 
Karate 2.5% EC (Obeng-Ofori and Ankrah, 2002). Other types are Dimethoate 
(400g/l) and Fipronil (25 g/1) (Koomson, 2008). Bacillus thuringiensis (Bt.) based 
products are also commonly used (Cobblah, 2000). Extracts o f seed, kernel, or leaves 
of neem have been found to be effective against P. xylostella (Bamby et al., 1989; 
Schmutterer, 1992; Verkerk and Wright 1996; Youdeowei, 2000; Charleston, 2002). 
Water extracts have proven to be most effective at concentrations as low as 12.5 g of 
seed per litre of water (Youdeowei, 2000). The use of neem seed water extract 
against the diamondback moth is common in some regions in Ghana according to 
Obeng-Ofori and Akuamoah, (1998). Morallo-Rejesus (1986) and Charleston et al. 
(2005) listed 88  plants mainly of the families Asteraceae, Euphorbiaceae and 
Meliaceae as having some insecticidal action against the diamondback moth.
In parts of Asia and Africa, farmers use cocktails of insecticide and spray more 
frequently without satisfactory control (Muckenfuss et al., 1992; Obeng-Ofori, 2000; 
Lohr, 2003; Mosiane et al., 2003). The pest is now widely known to have become 
resistant or tolerant to most insecticides such as Esfenvalerate, Diazinon, Permethrin 
(Miyata et al., 1986; Beck and Cameron, 1992; Walunj and Pawar, 2004). Some 
populations of the diamondback moth have developed resistance to certain B. 
thuringiensis based products (Tanaka, 1992, Tabashnik et al, 1992). However, of all 
the commercial biopesticides, Bt constitutes the most significant control option 
(Cherry et al, 2002).
29
The cabbage looper, Trichoplusia ni is the most difficult crucifer pest to control in 
parts of the USA and chemical control is difficult to achieve (Chalfant et al, 1979). 
Hill (1983) reported that the pest is resistant to carbaryl, parathion and methomyl. 
Capinera (1999) observed that even though, insecticide resistance is a problem in 
cabbage looper control, susceptibility varies widely among locations. In Thailand, 
Bacillus thuringiensis Berliner (Florbac FC, 8500 IU/mg) is used exclusively for 
control of T. ni (Rowell et al. 1992). Botanical insecticides such as rotenone are less 
effective, but neem functions as both a feeding deterrent and growth regulator 
(Capinera, 1999). Wyman (1992) reported that one to two applications of 
esfenvalarate provided excellent control. Obeng-Ofori and Ankrah (2002) reported 
that Neem extracts have great potential against several pests on cabbage in Ghana. 
The authors indicated that neem seed applied at the rate of 50 g/litre of water can be 
used as an alternative to synthetic insecticides to control cabbage pests and that, 300g 
of neem leaves and 100 g of hot pepper/litre of water are effective.
With regard to chemical control of the cabbage webworm Hellula undalis, Jayma and 
Roanld (2007) have drawn attention to the difficulty of chemical sprays penetrating 
the webbing produced by the larvae on cabbage. However, Rowell et al. (1992) 
reported that in Thailand, mevinphos (Phosdrin, 24EC) is effective in controlling the 
pest. In Guam Dibrom 8 EC has been observed to be most effective, providing 100% 
control (Muniappan and Marutani, 1992). Tests of Bacillus thuringiensis in Hawaii 
and elsewhere suggest that, they are only partially effective, and it is not 
recommended as standard treatments (Jayma et al., 2007).
30
2.9.2 Biological Control
Biological control, which involves principally the introduction, augmentation and 
conservation of natural enemies, is a valuable weapon in pest control on a number of 
crops. Biological control may be the exclusive method of control (Verkerk and 
Wright, 19%), or integrated with other methods such as the use of insecticides in 
some geographic areas and at certain times within the crop cycle (Loke et al., 1992; 
Lim, 1992; Klemm and Schmutterer, 1993).
Although over 130 species of parasitoids are known to attack various life stages of the 
diamondback moth, most worldwide control is achieved by relatively few 
Hymenopteran species belonging to the Ichneumonid genera, Diadegma and 
Diadromus-, the Braconid genera Microplitis and Cotesia; and the Eulophid genus 
Oomyzus (Mahmood et al., 2004; Sarfraz et al., 2005). The use of parasitoids alone 
has led to varying degrees of success (Mitchell et al., 1997a & b; Rowell et al., 2005; 
Mustata et al., 2006). Complete and partial controls of the diamondback moth by 
Cotesia plutellae have been reported in the Cape Verde Islands and Togo, 
respectively (Carl, K. P. British Museum Natural Hsitory personal communication).
Biological control of the eggs of Plutella xylostella varies from country to country. 
Liu et al. (2000) noted that rates of parasitism of the diamondback eggs by 
Trichogramma chilonis Ishii was very low and did not go beyond 1 - 11% in the 
suburbs of Hangzhou, China. According to Haji et al. (2002, cited in Pratissoli et al.,
2008), the use of Trichogramma species is increasing because it is cheap and easy to 
mass produce and can quickly suppress pest populations prior to crop damage. 
Laboratory evaluation of three species of done to identify the most suitable for use in
31
biological control programmes showed that T. atopovirilia (Oatmam and Platiner) had 
the strongest affinity for the eggs of the diamondback moth causing 42.33% 
parasitism (Pratissoli et al.. 2008). Mass release of Trichogrammatoidea bactrae 
Nakaraja in Thailand in the I990’s caused parasitism of between 16 - 45% of the 
diamondback moth eggs in unsprayed fields (Rowell, 2008).
Eighty percent parasitism of the larvae of the diamondback moth by Diadegma 
eucerophaga was reported by Sastrosiswojo and Sastrodihardjo (1986) and also by 
Ooi and Chua (1986); but Sastrodihardjo (1986) reported a low rate of below 30%. A 
combination of D. insulare and Microplitis plutellae (Mues) caused 68% parasitism in 
the first generation o f the diamondback moth in Canada (Putnam, 1968). In the 
Philippines, the introduction of Diadegma semiclausum led to a reduction of the 
diamondback moth infestation from an average of 18.7 larvae/plant to 9.8 larvae/plant 
(Poelking, 1992).
Ooi (1986) observed that even though Cotesia plutellae reduced the diamondback 
moth populations by 47 fold in the laboratory, field studies suggested limited ability 
of the parasitoid to control this pest because of its poor searching ability. Despite this, 
some introductions of this species have been successful (Muniappan and Marutani. 
1992). In Central America, attempts to complement the native Diadegma insidare 
(Cresson) with exotics have not been successful, but C. plutellae had been introduced 
and occasional recoveries made (Andrews et al., 1992). In the Caribbean, parasitism 
by the indigenous C. (Apanteles) glomeratus group was found to be low and erratic 
with the highest parasitism of 5%. However, the introduction of C. plutellae resulted
32
in parasitism of between 5.4 and 88.7% resulting in a marked reduction 
diamondback moth population (Alam, 1992).
Wide variations in parasitism by C. plutellae had been reported from locality 
locality and from country to country, even in areas with similar climates (Yaseen, 
1978; Ooi and Chua, 1986). Most reports indicate that the level o f parasitism by C. 
plutellae cannot exceed 60% (Ooi, 1979a & b; Ooi, 1992). It had been reported as the 
commonest parasitoid in Malaysia causing only 12 - 19%, or an average of 14.4% 
with a range of 0 - 33% (Ooi and Chua, 1986). Poelking (1992) reported 1 - 70% 
parasitism over different locations, seasons and years in the Phillipines whilst 
Morallo-Rejesus and Sayaboc (1992) recorded percentages between 1.9 - 16.5 in the 
same country. The latter authors also indicated that different strains have different 
abilities to parasitise, with exotic ones being superior. In the lowlands o f Malaysia, 
parasitism by Cotesia plutellae ranged from 12.7 - 48.6% (Loke et al., 1992). 
Martinez-Castillo et al. (2002) reported that in Central Mexico, biological control of 
Plulella xylostella larvae by Diadegma insulare could reach as high as 42.7% on 
cabbage.
Cotesia plutellae was not effective in places where percentage parasitism was 
between 2.3 and 35.8% but, in areas where parasitism ranged from 59.3 - 6 6 .6%, it 
was very effective in keeping the diamondback moth populations in check (Ooi. 
1992). A high level of parasitism of 78.8% at both larval and pupal threshold of about 
3 per plant was reported by Ooi (1986), but this was attributed to low host numbers. 
This author, however, noted that C. plutellae was not effective and could not prevent 
pest numbers from rising in the dry season. On the contrary, Ingham and Kfir, (1997)
33
indicated that parasitism by C. plutellae was effective when the diamondback moth 
populations were high. A combination of various parasitoid species had also given 
very good results (Yaseen, 1978; Ooi and Chua, 1986). Cotesia plutellae and O. 
sokolowskii had been reported to cause 10 - 60% larval parasitism at peak populations 
of the diamondback moth in parts of China and Romania (Liu et al., 2000; Mustata et 
al., 2006). In Kenya, the indigenous parasitoid species of Diadegma and Itoplectis, 
O. sokolowskii and an unidentified braconid caused a total of 20.8% parasitism while 
in Tanzania, C. plutellae, D. mollipla and O. sokolowskii caused a total of 10.1% 
parasitism (Lohr, 2003). This author also reported that the introduction of the exotic 
larval parasitoid D. semiclausum into these countries surpassed the combined 
parasitisation of P. xylostella by the indigenous parasitoids.
High levels of parasitism of the diamondback moth by pupal parasitoids belonging to 
the genera Tetrastichus and Diadromus (=Thyraella) Gravenhorst have been reported 
(Ooi and Keiderman, 1977; Keinsmeesuke el al., 1992). In several countries of South 
East Asia D. collcaris has been reared and released and contributes significantly to 
natural control of the diamondback moth pupae (Rowell, 2008). Oomyzus 
sokolowskii caused parasitism levels of up to 100% and 10% when acting as a primary 
or secondary parasitoid, respectively (Cock, 1985). Liu et al. (2000) reported 
secondary parasitism of 18% of the diamondback moth by this species in the 
laboratory. Mustata et al. (2006) considered O. sokolowskii as a dominant and 
constant secondary parasitoid in the field in Romania Its ability to also act as a 
hyperparasitoid does not make it a bad candidate as a primary parasitoid (Waterhouse 
and Norris, 1987; Mustata et al., 2006). This species was also the most abundant 
species recorded by other workers (Yaseen, 1978; Alam, 1992; Waiganjo, 1997). It
34
had also been used in combination with other species (Ooi, 1980; Chellia and 
Srinivasan, 1986) but very low parasitism rates ranging from zero to a maximum of 
20% were noted after the initial rate of 100%. Diadromus collaris Gravenhorst 
occurred when the diamondback moth populations were low late in the growing 
season and in the dry season when temperatures were high (Andrews et al., 1992; 
Rowell et al., 1992). Ooi and Kelderma (1977) and Ooi (1979a & b) considered 
Tetrastichus ayyari Rohw (=71 howardi = T. Israeli) to be of little importance as it 
occurred in negligible numbers.
Mass release of Trichogramma spp. has been investigated for Trichoplusia ni 
suppression. Oatman and Platner (1971) cited in Capinera (1999) observed that 
cabbage looper egg parasitism can be increased several fold by careful timing of the 
parasitoid release.
Baculoviruses have long been recognized as safe and effective biological pesticides 
for the control of Lepidopteran pests and in West Africa the baculovi ruses of Plulella 
xylostella are amenable to mass production and field application (Cherry, 2001). To a 
limited extent, baculoviruses have been used (Kadir, 1992; Cherry, et al., 2002). 
Osae et al. (2006) found that an East African strain of baculovirus was effective 
against a West African population of P. xylostella.
Trichoplusia ni NVP is effective, but has not been commercialised because of the 
narrow host range (Capinera, 1999). The author observed that home gardeners in 
parts of the United States of America sometimes collect and grind loopers dying of 
the virus, and concoct their own effective microbial control agent.
35
The practice of biological control has however, been hindered in some countries by 
the overuse of insecticides leading to ineffectiveness of Cotesia plutellae and other 
parasitoids of the diamondback moth in the cabbage ecosystem (Mustata, 1992; 
Waiganjo, 1997). The effects of insecticides on all developmental stages of 
parasitoids of the diamondback moth had been documented in parts of Asia and the 
USA (Keinmeesuke et al., 1992; Kao and Tzeng, 1992; Hu et al., 1997; Hill and 
Foster, 2000; Charleston et al., 2005). However, very little information exists on the 
effects of insecticides on parasitoids of the diamondback moth in Ghana (Obeng- 
Ofori, 2000).
Different authors have given contradictory observations on the adverse effects of 
insecticides on C. plutellae. Poelking (1992) noted that it resulted in reduced 
efficiency. Mustata (1992) and Waiganjo (1997) also attributed low levels of 
parasitism by a complex of diamondback moth parasitoids to the overuse and 
continued use of broad spectrum insecticides. Similarly, Alam (1992) noted that the 
failure of Cotesia plutellae to establish themselves in the field could have resulted 
from excessive use of chemicals. Some reports, however, indicated that the species 
was either tolerant or had achieved a certain level of resistance to insecticides in the 
field (Ooi, 1992; Liu et al., 2000; Rowell et al., 2005). In a field survey. Loke et al. 
(1992) recorded a high mean parasitism of 48.6%, even under very heavy insecticidal 
pressure. A mean parasitism of 75% by C. plutellae on the diamondback moth larvae 
was observed in spite of 1 - 3 weekly applications of insecticide cocktails (Lim. 
1992). Liu et al. (2000) similarly observed substantial rates of parasitism by the 
parasitoid on many occasions in China despite the heavy application of insecticide 
into the crop system. Intermittent Bacillus thuringiensis (Bt) sprays led to a reduction
36
in parasitism by C. plutellae (Morallo-Rejesus and Sayaboc, 1992). A strain, NRD-12 
(SAN 415) of Bt s.sp kurstaki was found to be more harmful to adults of C. plutellae 
than Bt s.sp kurstaki strain HD-1 (Kao and Tzeng, 1992). In addition, it has been 
observed that even though most of the other synthetic insecticides were harmful to the 
adults, the pupae were relatively tolerant (Mani and Krishnamoorthy, 1984).
Diadegma insulare seems to be less tolerant to pesticides than C. plutellae. 
Reduction of chemical insecticides allowed its full potential of to be realized, with C. 
plutellae becoming less dominant (Ooi, 1992). The inability of D. insulare to 
establish in some parts of Malaysia was reported to be partly due to high levels of 
insecticide use (Talekar et al., 1992). Hill and Foster (2000) observed that the 
Actinomycetes-derived produc, Spinosad caused 100% mortality to adults of D. 
insulare after eight hour exposure to leaves treated with the chemical. The 
effectiveness of Diadromus collaris (Gravenhorst) was reduced from 63% to 31% due 
to frequent use of broad spectrum insecticides (Rowell et al., 1992); but Bacillus 
thuringiensis, was found to exert less adverse effect it (Ooi, 1992). Keinmeesuke et 
al. (1992) observed that, even though Bt and certain synthetic insecticides had low 
toxicities to adults of the diamondback moth and the egg parasitoid, Trichogramma 
bactrae, few others were highly toxic to the diamondback moth eggs parasitised by 
this species and led to low emergence.
3 Integrated Pest Management
rhe problems associated with controlling P. xylostella and other l.epidopteran pests 
of cabbage with insecticides alone have stimulated interest in the use of a combination 
of strategies (Reddy and Guerrero, 2000; Lohr, 2003). Examples of successful
37
Integrated Pest Management (IPM) strategies abound in the literature (Talekar and 
Griggs, 1986; Lim, 1990; Talekar and Yang, 1991; Liu, 2001). There is also 
widespread recognition of the crucial role played by natural enemies (Hamilton et al..
2004). Emphasis has been placed on the use of selective toxicants, particularly 
Bacillus thuringiensis-based products, which have little or no adverse effect on key 
parasitoids (Verkerk and Wright, 1996; Abdel-Razek et al., 2006), or spraying of 
insecticides only when predetermined thresholds have been reached (Chen and Su. 
1986; Reddy and Guerrero, 2000).
At the Asian Vegetable Research and Development Centre (AVRDC), a successful 
integrated pest management programme had been developed to effectively control the 
diamondback moth by combining the use of the parasitoid Diadegma semiclausum 
and Bacillus thuringiensis (Talekar et al., 1992; Talekar, 1992). Other methods 
include a combination of two or more of sprinkler systems, C. plutellae, granulosis 
virus and insecticides (Nakahara et al.. 1986; Andrews el al., 1992; Loke el al.. 1992). 
A combination of yellow sticky traps for diamondback moth adults and action 
threshold for larvae had given good results in Thailand (Rushtapakomchai ei al.. 
1992; Hallett et al., 1995). Reddy and Guerrero (2000) reported that an IPM 
programme based on the pheromone trap catch threshold of eight moths per trap per 
night, which included utilization of C. plutellae, (250 adults ha'1), the predator 
Chrysoperla carnea (2500 eggs ha'1), neem based chemical nimbecidine (625 ml ha' 
'), B. thuringiensis (500 ml ha'1) and the synthetic insecticide Phosalone (2.8 litre ha' 
') induced reduction of trap catches, egg and larval populations. It also led to 
economic savings of $410 ha'1 in 1997. In Ghana the advent of the IPM-Farmer Field 
Schools (IPM/FFS) programmes in 1999-2001 encouraged farmers to do Aero-
38
Ecosystem Analysis (AESA) before applying any control measure. The AESA 
involved assessment of the health of the plant, the moisture content of the soil and the 
role of the different arthropods with special reference to the presence of natural 
enemies and, thus, made informed decisions (Youdeowei, 2002).
Muniappan and Marutani (1992) observed that in Guam, a combination of Dibrom 8 
EC, natural enemies and insecticides can potentially give satisfactory control of 
crucifer pests. Wyman (1992) reported that the integration of biological control, 
cultural control, host plant resistance and other management techniques will play an 
increasingly important role in insecticide resistant management for all crucifer pests.
39
CHAPTER THREE
3.0 SEASONAL VARIATION OF PARASITOID-HOST ASSOCIATIONS AND 
EFFECT OF INSECTICIDES
3.1 Introduction
The most damaging insect pests of the common cabbage. Brassica oleracea var. 
capitata are the Lepidopterans: Plutella xylostella, Pieris rapae, Trichoplusia ni and 
Hellula undalis (Talekar, 1992; Anene and Dike, 1996; Dobson el al., 2002; Hamilton 
et al., 2004). The relative importance of these species varies from country to country 
or may even be seasonal (Harcourt et al., 1955, Oatman, 1966; Bell and McGeoch, 
1996; Liu et al., 2000). However, P. xylostella is cosmopolitan and it is considered 
the most important pest worldwide causing production losses of up to 60% (Pratissoli 
et al.. 2008). For this reason, insecticides are frequently applied on cabbage in order 
to produce marketable heads. This practice has led to the development of multiple 
resistance to insecticides by P. xylostella (Ninsin, 1997; Abdel-Razek et al., 2006).
In order to address this problem, the use of biological control agents and the 
development of integrated pest management programmes, are considered feasible 
options (Hill and Foster, 2000; Pratissoli et al., 2008). Significant control by 
biological control agents had been reported in various countries (Liu et al, 2000; 
Mahar et al., 2004). Despite this recognition, very few studies have been done to 
assess the effect of commonly used insecticides and insect growth regulators on the 
natural enemies (Fan and Ho, 1971; Martinez-Castillo et al., 2002). In Ghana. Ninsin 
(1997) observed that various synthetic insecticides applied on cabbage had adverse
40
effects on non-target insects and other beneficial organisms. Many pesticides are also 
known to be more toxic to consumers and natural enemies than to the pests 
(Wilkinson et al., 1975; Schuster, 1994; Pratissoli et al., 2008).
Mani and Krishnamoorthy (1984) observed that some insecticides had adverse effects 
both on the cocooned stages and adults of C. plutellae an important parasitoid of P. 
xylostella in parts of India. However, contradictory reports on the adverse effects of 
insecticides on C. plutellae have also been given by various authors. Ooi (1992), Kao 
and Tzeng (1992), Liu et al. (2000), Rowell et al. (2005) indicated that this species 
was either tolerant to or had achieved a certain level of resistance to insecticides in the 
field. In Ghana, little or nothing is known regarding the relative and seasonal 
importance of the Lepidopteran pests of cabbage, the identity of their parasitoids and 
the effect of commonly used insecticides on the parasitoids (Obeng-Ofori, 2000).
The objective of this study was to determine the seasonality of parasitoid-host 
associations on cabbage, levels of parasitism and the effect of the commonly used 
insecticides on the development of the major parasitoid.
3.2 Materials and Methods
3.2.1 The Experimental Site
The study was carried out on plots at the Weija Irrigation Company (WE1CO) site at 
Tubaman near Weija in the Greater Accra region (Fig. 3.1) between 1996-1997 and 
2000-2008. This site was chosen for four main reasons: The commercial production 
of cabbage and other vegetables including export crops that spans over 10 years 
(Annual Reports WE1CO, 1999) with the consistent use of insecticides against the key
41
pests of cabbage. Besides, Plulella xylostella was known to be resistant to the 
common insecticides in use in that area (Annual Reports WE1CO, 1999). Field 
surveys were also carried out to investigate the occurrence of the major pests and 
associated parasitoids in parts of the Greater Accra, Eastern, Volta, Western and 
Ashanti regions (Fig. 3.1).
The WE1CO study site is located at latitude 5° 31’ N and longitude 0° 21’ W. It lies 
about 21 km west of the city of Accra on the road to Winneba, Cape Coast and 
Takoradi. It is about 4.2 km. from the said link road towards the sea (Atlantic Ocean) 
in the south. It is a generally windy area with average minimum and maximum 
temperatures of 23 °C and 31 °C, respectively. Relative humidity during the study 
period ranged from 31 - 62%, with an average of 44%.
3.2.2 Planting
Planting of the cabbage variety KK cross was done in the major and minor rainy 
seasons as well as the dry season.
The first season planting was done from April to July of 1996 to coincide with the 
major rainy season. Cabbage seeds were nursed for four weeks and transplanted in a 
RCBD on 2nd May. Prevailing temperatures at the experimental site ranged from 23 
°C - 30 °C.
The second planting was done from August to December of 1996 and fell within the 
minor rainy season. Cabbage seeds were nursed and transplanted on 4111 October in a 
RCBD. Prevailing temperatures at the site ranged from 23.5 °C - 31.5 °C.
42
The third planting was done in the dry season between January and April 1997. 
Transplanting of seedlings was done on 28lh February after four weeks in the nursery 
in a RCBD. Prevailing temperatures ranged from 26 °C - 31 °C.
3.2.3 The Experimental Layout
The experiment consisted of four treatments arranged in a randomised complete block 
design (RCBD) with four replications. The experimental area of 38.64 m2 was 
separated from other vegetable farms by approximately 100 meters. The land was 
ploughed and harrowed and then watered before the beds were raised using a hoe. 
Each bed was later leveled by raking and pieces of stone and other unwanted 
materials were removed before transplanting of cabbage seedlings. Each plot 
measured 4.2 by 2.3 meters. There were 3 rows per plot and each row had 7 plants, 
giving a total of 21 plants per plot The distance between blocks was 1.5 m and 
between plots in a block was 1 m. Plant spacing was 60 cm within rows and 75 cm 
between rows.
3.2.4 Treatments Applied
The treatments applied were:
1. Lambda-Cyhalothrin formulated as Karate 2.5 E.C at the rate of 2.4 ml/ litre of 
water
2. 1.0 g Bacillus Ihuringiensis wettable powder (Dipel 2x)/ litre of water
3. 50 g neem (Azadirachta indica) seed powder/litre of water extract (applied only 
once)
4. Unsprayed Control (Water only)
43
Neem Seed Water Extract was prepared as follows:
Dried neem seeds were purchased and stored in jute sacks in an air-conditioned room 
with an average temperature of 23.0 ± 2 °C and relative humidity of 45 ± 1.0%. 
Based on the concentration of 50 g/litre of water, 194.1 g. were weighed and ground 
using a Moulinex mill of capacity 95.1 cm3. The mill was, each time, filled to the 
brim and the seeds milled for about two minutes into fine powder. The powder was 
then mixed with the 3.9 litres of water and three spoonfuls of *Omo’ detergent was 
added to reduce the surface tension of the mixture. The mixture was kept overnight 
and then sieved through a fine plastic strainer to obtain the extract
3.2.5 Fertiliser Application
The dose and timing of application of fertiliser recommended by Sinnadurai (1992) 
were followed. This involved a split application of 450 kg/ha of 15:15:15 NPK at 
seven days and twenty seven days after transplanting. A single dose of Sulphate of 
ammonia at 250 kg/ha was also applied at 34 days after transplanting. Basal 
applications of the fertilizer were done at a distance of 10 - 15 cm away from the plant 
at a depth of 5 - 6 cm. For each plant, 10 g. of the fertilizer was applied in the 
evenings as recommended.
3.2.6 Insecticide Application
The concentrations of the lambda cyaholothrin and Bacillus thuringiensis used were 
based on manufacturer’s recommendations for field applications. For the neem seed 
water extract in addition to the recommended rates, a preliminary study was done to 
determine the concentration because of the varying potency cffects of neem. The 
dosages tested were 25 g/l, 50 g/1 and 75 g/1. The application rates in litres per
44
hectare required for the total land area of 38.64 m2 for the experiment is shown in 
(Table 3.1). The neem seed water extract treatment was added during the minor rainy 
and dry seasons. This was because after the major rainy season study, it was observed 
that damage was high on the unsprayed plots and parasitoid activity was very low till 
about 5 weeks after transplanting. The additional neem treatment was, therefore, 
imposed to complement the effect of the parasitoids during the first four to five weeks 
before pest numbers built up to appreciable levels.
Table 3.1: Volumes of Insecticides Applied to Cabbage Plants
Insecticide Fourth WAT 
Quantity/ha
Sixth WAT 
Quantity/ha
Eighth WAT 
Quantity/ha
Karate 4.661 7.45 1 9.321
Bt 1.94 kg. 3.11 kg. 3.88 kg.
NSWE 194.1 kg. nil nil
NSWE=Neem seed water extract WAT= Week after transplanting
The insecticides were applied using a calibrated 15 - litre tank capacity knapsack 
sprayer (Cooper Pegler, U.K. Ltd.) fitted with a fine plastic hollow cone nozzle 
obtained from (Chemico Chemical Ltd., Ghana). Bionex was added to the spray 
solution as a spreader. Insecticide applications started on the fourth week after 
transplanting. This was done in the evenings after the first sampling and. thereafter, 
every two weeks, except for the neem treatment which was applied only once in the 
fourth week after transplanting. Separate spray equipment was used for each 
treatment to avoid contamination.
45
3.2.7 Incidence and Seasonal Abundance of Pests and Parasitoids
Sampling for insects on the experimental plots was started between eighteen and 
twenty days after transplanting when the first signs of insect attack on the leaves were 
observed and was done till harvest. Sampling was carried out once a week on the 
seven central plants in each of the treatment plots from 08 hours in the morning. 
During sampling, all developmental stages of insects on the five upper leaves as well 
as the two leaves surrounding the bud and the bud itself were carefully collected into 
petri dishes lined with filter paper and provided with a piece of cabbage leaf. Larvae 
which fell to the ground or spun a thread to escape were collected. On plants with 
multiple heads, the same head was tagged and sampled each time. All samples were 
labeled and taken to the laboratory for rearing until adult emergence of pest or 
parasitoid for subsequent identification and counting.
A replication of the experiment could not be done for another year because two 
cropping seasons were lost to the diamondback moth. In the year 2000 - 2001 a 
fanner’s farm at the Weija Irrigation Company site was sampled for three cropping 
seasons. It was considered as a farmer’s practice.
The farmer applied various insecticides such as Rimon (a Benzoylphenyl Urea), 
Lamda-Cyhalothrin (Karate), Bacillus thuringiensis (Biobit) and neem seed water 
extract on his plots. He applied insecticides from two weeks after transplanting or 
when in his opinion there were many insects. The cabbages were planted in long 
rows. Insects were sampled as described for the experimental plots.
46
3.2.8 Laboratory Rearing of Pests
The eggs, larvae and pupae of the pests collected in the field were kept separately in 
petri-dishes. The eggs still attached to cabbage leaves were placed on moist filter 
paper in petri dishes on the laboratory bench for incubation. The larvae were 
separated and each was placed on a piece of cabbage leaf on a wet filter paper in a 
petri dish. Each larva was transferred into a clean petri dish with a fresh piece of 
cabbage leaf daily and observed until it pupated or either parasitoid larvae or pupae 
emerged. Emerged pupae of pests were kept in petri dishes lined with dry filter paper 
till adult emergence. The insects that emerged were stored in 70% alcohol or 
mounted for identification. All the rearings were done at a temperature of 23 ± 2 °C 
and relative humidity of 45 ± 1%.
3.2.9 Weekly Parasitism Trends by Cotesia plutellae and Euplectrus laphygmae in 
Relation to Plutella xylostella and Trichoplusia ni
All the parasitoid larvae, pupae and adults emerging from the field collected immature 
stages of pests from the seven central plants of all the treatments were recorded daily 
in the laboratory. Parasitoid larvae or pupae that emerged from hosts were each kept 
in separate glass tubes plugged with cotton wool until the adults emerged. The larvae 
and pupae of pests that did not develop into adults were dissected to determine 
whether they had been parasitized and numbers recorded. Parasitism was therefore 
determined from rearing of pests as well as from the dissections. The parasitoids that 
emerged from its host were recorded for each week’s sample to determine parasitism 
and relationship between the parasitoids and the host till harvest of the cabbage. The 
parasitoids that emerged were stored in 70% alcohol or mounted for identification. 
All insects were maintained at a temperature of 23 ± 2 UC and relative humidity of 45
47
± 1%. Mean percentage parasitism was determined for all the treatments for 
comparison.
3.2.10 Identification of Pests and Parasitoids
The pests and parasitoids collected or observed were identified using the reference 
collections at the Entomology and Nematology Department of the University of 
Florida, USA. Specimens were also sent to CABI Bioscience, U.K. for confirmation 
and in some cases for the initial identification.
3Jt.ll Emergence and Mortality of Cotesia plutellae Exposed to Insecticides
Emergence rates of C. plutellae adults were determined for all the parasitoid pupae 
that emerged from the pests collected from the seven central plants for all the 
treatments in the three seasons. In addition, all the pupae of C. plutellae were also 
collected from the seven central plants for all the treatments 3 weeks after 
transplanting during the major rainy season of May to July and the dry season from 
February to April on a single crop. Each pupa was kept in a separate glass tube and 
plugged with a piece of absorbent cotton wool till emergence of the adults in the 
laboratory at an average temperature of 23 ± 2 °C and RH of 45 ± 1 %. On 
emergence, each parasitoid adult was identified. Those that did not emerge after two 
weeks were kept for a further three weeks. Non-emergence after this period was 
considered to be mortality due to the insecticide. They were then dissected to 
determine their state of development and species where possible.
48
3.2.12 Laboratory Studies on Mortality of Adults and Emergence of Pupae of C. 
plutellae Exposed to Different Insecticides
A synthetic insecticide Lambda-Cyhalothrin marketed as Karate 2.5 EC, a 
biopesticide Bacillus thuringiensis as wettable powder and a commercial neem 
formulated product, Neemazal, were evaluated against the most abundant parasitoid 
Cotesia plutellae. All the tests were carried out in the laboratory with a mean 
temperature of 28 ± 2 °C and relative humidity of 55 ± 1%. Two parameters (direct 
mortality to adults and non-emergence from pupae) were used to determine the effect 
of the insecticides (Gaitonde, 1978).
Two methods of application were used to determine the residual effect and toxicity of 
the three insecticides to the pupae and adults of C. plutellae. These were the filter 
paper and direct contact application methods, respectively (Gaitonde, 1978). 
Concentrations of insecticides used were 2.4 ml. Karate/litre of water, 1.0 g Bacillus 
thuringiensis wettable powder/ litre of water, 1.0 ml. Neemazal/litre of water and 
water only as control.
3.2.12.1 Filter Paper Method
A strip of filter paper measuring 11 cm in diameter was cut into two and one half 
dipped into the insecticide solution, air dried for 20 minutes and placed in a 
transparent jar measuring 12 cm deep and 9.5 cm in diameter as described by 
Wilkinson el al. (1975). The jar was covered with nylon mesh secured with a rubber 
band. Ten day - old adults of C. plutellae were introduced into the set up through a 
slit made in the mesh which was subsequently plugged with a cotton wool. The 
parasitoids were held in the jar for six hours. A piece of cotton wool soaked in 10%
49
honey solution was provided as food through a slit made in the side of the jar. After 
six hours, the parasitoids were transferred into a clean jar containing a piece of cotton 
wool soaked with 10% honey solution and observed for a further 48 hours. A control 
was set up with the other half of the filter paper soaked with water. Adult mortality 
was recorded at the end of the 6-hour exposure period, 24 hours and 48 hours after 
treatment (Gaitonde, 1978). Each treatment was replicated four times and each 
replicate had 10 adults of C. plutellae
3.2.12.2 Direct Application Method
For the direct contact insecticide application, two methods were used to determine the 
direct effect of contact application of the test insecticides on the adult parasitoids. In 
the first method, a piece of cabbage leaf with the same dimensions as the filter paper 
described above was dipped once in each treatment. This was done to simulate 
natural conditions in the field as much as possible. The treated leaf was immediately 
placed in a transparent jar and 10 one-day old adults of C. plutellae were introduced 
and provided with food as described above. The parasitoids were transferred after six 
hours and mortality recorded after 48 hours following the same procedure described 
above.
For the second method, adult parasitoids were introduced into a jar immediately after 
one puff of the insecticide solution had been sprayed into it from an Atomiser. The 
same procedure, with regard to feeding and recording mortality described above was 
followed. A control was set up using water in place of the insecticide solution. Each 
treatment was replicated four times.
50
A similar experiment was carried out using the pupae of C. plutellae. Each of the 
treatments was replicated four times and each replicate had 10 pupae. The filter paper 
and cabbage leaf procedures described above were followed for the pupae of C. 
plutellae. For the spray method, 10 day - old pupae were placed uniformly on a glass 
plate and sprayed quickly with one puff of the insecticide from an Atomiser filled 
with 2 ml of the insecticide solution.
For the direct contact application method, the pupae were left to air-dry on the 
laboratory bench for 20 minutes after the 6 hour insecticide exposure period. After 
that each pupa was transferred into a clean separate specimen tube which was then 
plugged with cotton wooland left to stand in trays on the laboratory bench till adult 
emergence. For the control experiment, pupae were treated with water. Failure of 
pupae to emerge was taken as mortality due to the effect of the treatment Pupae 
which failed to emerge were kept and observed for a further three weeks after which 
they were dissected to determine their state of development (Day, 1994).
3.2.13 Statistical Analysis
All mortality data were corrected for natural mortality using Abbot’s formula (Abbot 
1925). All percentages were transformed using arcsine transformation and counts 
transformed using natural log prior to Analysis of Variance. Mean separation was 
done using Duncan’s Multiple Range Test (DMRT). Pearson’s correlation was used 
to determine the relationship between populations of P. xylostella and its parasitoid. 
All the analyses were done with the Statistical Programme for the Social Sciences 
(SPSS) version 16 software.
51
3.3 Results
33.1 Incidence and Seasonal Abundance of Lepidopteran Pests
Larvae and pupae of six species of Lepidoptera were recorded on cabbage in all the 
three seasons at the Weija site. Five of the species were pests that fed directly on the 
plant and caused damage. These were the diamondback moth, Plutella xylostella, the 
cabbage looper. Trichoplusia ni, the cabbage webworm, Hellula undalis, the leaf 
worm Spodoptera littoralis and the African bollworm, Helicoverpa armigera. The 
distribution map of the pests recorded in this study is shown in Figure 3.1.
The sixth species, the beet webworm, Spoladea recurvalis was occasionally found on 
cabbage, but was usually associated with the weed Cyperus rotundus (nut grass). 
Single specimens of Spodoptera triturata (Walker) were collected twice on cabbage 
at the experimental site during the minor rainy season. It was also collected once at 
the University of Ghana farms on Legon campus during the minor rainy season whilst 
the cutworm, Agrotis sp was recorded at Denche in the Western Region during a field 
survey.
52
PEST DISTRIBUTION MAP
Figure 3.1: Distribution Map of Pests of Cabbage in Southern Ghana
In vegetable growing areas (Fig.3.1 and Appendix 3.1) where fanners were 
encouraged to diversify under the Agro-skills Development and Farmer Field Schools 
Programme of the FAO/UNDP Poverty Reduction Programme of 1999-2001, the 
diamondback moth was not observed. The cabbage flea beetle, Phylothreta 
cheiranthei Weise, and Hellula undalis were present in the nursery and transplanted 
cabbage. Subsequent surveys in 2005 in Dodowa and Moyose in the Greater Accra 
region showed that the diamondback moth was still not present. The diamondback 
moth was also not recorded on cabbage in villages within the Homasi concession of 
Anglogold Ashanti (Ghana) Ltd. near Obuasi Mines in the Ashanti region where 
peasant farmers were introduced to the cultivation of cabbage in a vegetable 
diversification programme (Darpaah, 2008).
53
In general, it was observed that the abundance of pests at the experimental site was 
dependent on the prevailing season. In all seasons damage was observed three weeks 
after transplanting. The relative percentage abundance of pest species from the 
unsprayed plots for the three seasons is shown in Table 3.2. P. xylostella was most 
abundant in the dry season (69.6%) while Trichoplusia ni was most abundant in the 
major rainy season (79%). However, S. littoralis was most dominant in the minor 
rainy season, constituting 59% of the pest population. Helicoverpa armigera and H. 
undalis occurred in significant numbers during the dry season, but were both absent 
during the major rainy season
Table 3.2 Relative Abundance of Larvae of Lepidopteran Pests of Cabbage in 
the Three Cropping Seasons on the Unsprayed Plots at the 
Experimental Site, Weija.
Percentage Abundance
Season Total No. 
of larvae
P.
xylostella
T.
ni
S.
littoralis
H.
armigera
H.
undalis
S.
recurvalis
Major Rainy 329 20.4° 79.0a 0.6C 0.0k 0.0" 0.0b
Minor Rainy 227 30.4b 9.3b 59.0” 0.4b 0.9b 0.0b
Dry 296 69.6° 11.5b 5.4b 7.1“ 3.4* 3.0*
TOTAL 8S2 40.0 37.0 17.9 2.6 1.4 1.1
Means in the same column with same letters as superscripts are not significantly 
different at the 5% confidence level (Duncan's Multiple Range Test).
54
On the farmer's farm, where various insecticides were applied, Plutella xylostella 
formed 88.8% of the total pests and T. ni formed 5.3% in an annual production of 
cabbage (Table 3.3). Plutella xylostella was significantly most abundant during the 
minor rainy season and T. ni occurred in significant numbers during the major rainy 
season. Hellula undalis populations were highest in the dry season and least in the 
minor rainy season. H. armigera was most abundant during the dry season.
Table 3J: Relative Abundance of Larvae of Lepidopteran Pests of Cabbage in 
the Three Cropping Seasons on Farmer’s Plots at Weija.
Percentage Abundance
Season Total No. 
of larvae
P.
xylostella
T.
ni
s.
littoralis
H.
armigera
H.
undalis
£
recurvalis
Major Rainy 144 45.lb 36.1“ Thise 02. lb 09.0b 1.4*
Minor Rainy 958 97.1“ 00.6C 00.9C 00. lb 01.0C 0.1“
Dry 69 47.8b 05.8b 10.1“ 18.8“ 17.4“ 0.0“
TOTAL 1171 88.8 05.3 02.1 01.5 02.0 0 3
Means in the same column with same letters as superscripts are not significantly 
different at the 5% confidence level (Duncan’s Multiple Range Test).
33.2 Comparative Abundance of Larvae of Lepidopteran Pests on Unsprayed 
Experimental Plots and on Farmer’s Plots at Weija
On both experimental plots and farmer’s plots, Plutella xylostella was the most 
abundant during the study. There was a significantly higher number of P. xylostella 
larvae on the farmer’s plots compared with the experimental plots (p < 0.05) (Table
55
3.4). Conversely, Trichoplusia ni and S. littoralis were significantly more abundant 
on the experimental plots.
Table 3.4: Comparative Percentage Abundance of Lepidopteran Pests on
Experimental Plots and on Farmer’s Plots
Plot
Total No. 
of larvae
P.
xylostella
T.
ni
S.
littoralis
H.
armlgera
H.
undalis
S.
recurvalis
Experimental
Plots 852b 40.0b 37.0* 17.9* 2.6* 1.4* 1.1*
Farmer's Plots 1171a 88.8* 5.3b 2.1b 1.5* 2.0* 0.3*
Means in the same column with same letters as superscripts are not significantly 
different at the 5% confidence level (Duncan’s Multiple Range Test).
33 3  Population Density of Larvae of P. xylostella, T. ni and S. littoralis on Cabbage in 
the Three Seasons on Experimental Plots
The population density of P. xylostella was highest in the dry season. A significantly 
high mean density of 0.29 ± 0.05 larvae per plant (p < 0.05) (Table 3.5) was recorded 
during this season compared with the other pests. The least was observed during the 
major rainy season. There were many instances where several larvae of the 
diamondback moth were observed drowned in water that had collected on cabbage 
leaves after rains. However, it was the only species that occurred in significant 
numbers for all the seasons. On the other hand, a significantly high mean density of 
0.60 ± 0.11 larvae per plant (p < 0.05) of T. ni was recorded in the major rainy season 
compared with the other seasons (Table 3.5). With regard to S. littoralis. a 
significantly high mean density of 0.39 ±0.10 larvae per plant (p< 0.05) was recorded 
in the minor rainy season compared with the other seasons.
Table 3.5 Population Density per Plant of Larvae of P. xylostella, T. ni and S.
littoralis on Cabbage in the Three Seasons
Pest Major Rainy Season Minor Rainy Season Dry Season
S. littoralis 0.003 ± 0.003** 0.39 ± 0.10*** 0.05 ± 0.02**
P. xylostella 0.15 ± 0.04** 0.20 ± 0.07‘b* 0.29 ± 0.05b*
T. ni 0.60 ±0 .11b** 0.06 ± 0.03 b* 0.09 ± 0.02**
Means in the same column with same letters as superscripts are not significantly 
different at the 5% confidence level (Duncan’s Multiple Range Test).
*Means in the same row with same number of asterisk are not significantly different 
at the 5% confidence level (Duncan’s Multiple Range Test).
33.4 Incidence and Seasonal Abundance of the Parasitoids
A total of 15 species of parasitoids, some of which also acted as hyperparasitoids 
were reared from the Lepidopteran pests at the experimental site (Table 3.6). Cotesia 
plutellae was the most important parasitoid of the major pest P. xylostella as well as 
T. ni, and was present throughout the year whenever cabbage was grown. Euplectrus 
laphygmae (Ferriere) was recorded in the major rainy season and minor rainy season 
and parasitized third instar larvae T. ni. None was collected in the dry season 
(February - March) when the incidence of T. ni was extremely low. It also parasitized 
S. littoralis on four occasions during the minor rainy season. The parasitoids C. 
curvimaculatus, Notanisomorphella sp and the two Tachinid species were specific to
S. littoralis and they each parasitized this species only on two occasions during the 
minor rainy season and dry season. Only a single H. undalis was parasitized by C. 
plutellae. No parasitism of H. armigera was recorded and no egg parasitoids were 
observed from any of the pests during the study period.
57
Table 3.6 Seasonal Occurrence of Parasitoid/Hyperparasitoid Species and 
Lepidopteran Host Species on Cabbage at the Experimental Site
Parasitoids/
Hyperparasitoids
Host species Seasonality of 
Parasitoid
Ichneumonoidea
Cotesia plutellae P. xylostella and T. ni larvae All 3 seasons
Chelonus curvimaculatus S. littoralis larvae MiRS
Charops sp. T. ni & 5. littoralis larvae MiRS & DrS
Chalcidoidea
Brachymeria sp. T. ni larva via Charops sp MiRS & DrS
Hockeria sp. P. xylostella larvae MiRS
Elasmus sp. P. xylostella larvae via C. plutellae DrS
Euplectrus laphygmae T. ni. & S. littoralis larvae MaRS&MiRS
Notanisomorphella sp. S. littoralis larva DrS
Oomyzus sokolowskii P. xylostella larvae via C. plutellae MaRS
P. xylostella larva-pupa
Tetrastichus atriclavus S.L T. ni larvae via C. plutellae MaRS
Pediobius sp. P. xylostella larvae & pupae MaRS
Trichomalopsis sp. P. xylostella larvae via C. plutellae MaRS
T. ni larvae via C. plutellae MaRS
Ceraphronoidea
Aphanogmus reticulatus P. xylostella pupae via C. plutellae MaRS
T. ni larvae via C. plutellae
Tachinidae
Blepharella sp near vasta S. littoralis larval-pupal MiRS
Peribaea orbata S. littoralis larva MiRS
MaRS = Major rainy season MiRS = Minor rainy season DRS= Dry season 
via C. plutellae means Parasitism of C. plutellae occurred inside P. xylostella.
58
Elsewhere in Ghana, C. plutellae was recorded in parts of the Greater Accra Region at 
the Kotobabi-PIant Pool (Accra), La Bawaleshi near Legon, Miotso near Dodowa, 
Dawhenya, and at Mampong in the Eastern region. The facultative hyperparasitoid O. 
sokolowskii was recorded in Dawhenya.
Cotesia plutellae was the dominant and most important parasitoid observed. Seven 
hundred and six (706) parasitoids were recorded from P. xylostella in the three 
seasons and 92% were C. plutellae. The rest (8%) comprised of facultative 
hyperparasitoids; O. sokolowskii, Aphanogmus reticulatus, Trichomalopsis sp. 
Elasmus sp. and two primary parasitoids Pediobius sp. and Hockeria sp. Thus, the 
primary parasitoid C. plutellae was attacked by 4 parasitoids. In the major rainy 
season when T. ni was more abundant than P. xylostella, of the 110 parasitoids 
observed from the former, 60.9% and 35.5% consisted of C. plutellae and E. 
laphygmae respectively. The remaining included the hyperparasitoids Trichomalopsis 
sp. A. reticulatus and Tetrastichus atriclavus. Only 12 out of the 152 S. litloralis 
larvae were parasitized by the five species of parasitoids recorded from it during the 
whole study period at the experimental site.
Cotesia plutellae and Oomyzus sokolowskii were the only primary parasitoid and 
facultative hyperparasitoid respectively, observed on the farmer’s farm. Cotesia 
plutellae parasitized 1% of the total diamondback moth larvae of 1,040 (88.8%) 
sampled. The parasitoids were observed during the major rainy season in May. Out 
of the twelve diamondback moth larvae parasitized by C. plutellae. 42% were 
hyperparasitised by O. sokolowskii
59
Based on the parasitoids and hyperparasitoids of P. xylostella and T. ni, the trophic 
relationships among species on cabbage is presented in figure 3.2.
Figure 3.2: Trophic Relationships among P. xylostella, T. ni and Parasitoids and
Hyperparasitoids on Cabbage.
33.5 Weekly Parasitism Trends by C. plutellae in Relation to P. xylostella
Population build up of C. plutellae in relation to its host the diamondback moth 
during cabbage production on the unsprayed plots was a density dependent 
relationship where an increase in diamondback numbers resulted in a corresponding 
increase in parasitism (Figs. 3.3 - 3.5). The results indicated that there was a distinct 
time lag of one to two weeks in the major rainy and minor rainy seasons (Figs. 3.3 
and 3.4) after which parasitism became closely synchronized with host numbers from 
25 DAT in the former season.
60
♦  P. xylostella 
C. plutellae
18 25 32 39 46 53 60 74
PEST DIRBU OUENTMAENR♦N—
Figure 3 J :  Weekly Parasitism Trends by C. plutellae in Relation to P. xylostella
in the Major Rainy Season. Coefficient of Correlation r = 0.97
PEST DIRBU OUENTMAENR♦N—
— *— P. xylostella 
— * —  C. plutellae
Figure 3.4: Weekly Parasitism Trends by C. plutellae in Relation to P. xylostella
in the Minor Rainy Season. Coefficient of Correlation r = 0.55
61
In the dry season when build up of the pest was highest, there was no time lag 
between host numbers and parasitism (Fig. 3.5) and parasitism rates also increased as 
diamondback numbers increased.
Figure 3.5: Weekly Parasitism Trends by C. plutellae in Relation to P. xylostella
in the Dry Season. Coefficient of Correlation r = 0.66
The association between diamondback numbers and parasitism varied among the
seasons and was strongest in the major rainy season. The Correlation coefficient r
between diamondback numbers and numbers parasitized during the major rainy
season was r = 0.97 whilst in the minor season r = 0.55. In the dry season the
Correlation coefficient r = 0.66. The Coefficient of determination, R2 which is
defined as the variation in parasitism that is dependent on the variation in
diamondback numbers was R2 = r2 = 0.9709212 = 0.9427 = 94.3% in the major rainy
season. Hence, 94.3% of the variation in parasitism was due to the variation in host
numbers. In the minor rainy season, 30.8% of the variation in parasitism was due to
the variation in diamondback moth numbers whilst in the dry season it was 44.0%. It
was very common to find many cocoons of C. plutellae scattered on the leaves at
62
harvest of the cabbage in the major rainy and dry seasons. The overall Correlation 
Coefficient r. between the diamondback numbers and C. plutellae was 0.51. The 
Coefficient of determination R2 = 0.262. Hence, in an annual production of cabbage 
26.2% of the variation in parasitism is due to the variation in the number of the 
diamondback moth.
33.6 Weekly Parasitism Trends by C  plutellae and E. laphygmae in Relation to T. ni
The relationship between the parasitoids C. plutellae and E. laphygmae and their host 
T. ni. was considered only for the major rainy season because no parasitism was 
observed during the minor rainy season and the population of the pest during the dry 
season was so low that any meaningful comparison was not possible. There was one 
week time lag after which the two parasitoids generally acted in a density dependent 
manner and the population started to build up around 25 DAT (Fig 3.6).
Figure 3.6: Weekly Parasitism Trends by C. plutellae and E. laphygmae in
Relation to T. ni in the Major Rainy Season
63
3.3.7 Parasitism of P. xylostella by C. plutellae in Three Seasons
Wide seasonal variations were observed in the rates of parasitism. Mean percentage 
parasitism of P. xylostella by C. plutellae was highest (p < 0.05) during the major 
rainy season (68.6% ± 12.9) and least during the minor rainy season (9.9% ± 7.1). 
There was no significant difference (p > 0.05) in the rates of parasitism between the
Figure 3.7: Seasonal Variation in Mean Percentage Parasitism of P. xylostella by
C. plutellae
Bars with same alphabets are not significantly different at the 5% 
confidence level (Duncan’s Multiple Range Test).
33.8 Parasitism of P. xylostella by C. plutellae on Insecticide Treated Plots
Parasitism of larvae of P. xylostella was substantial despite the insecticide pressure 
imposed. Parasitism rates were higher on the Karate treated plots but these were not 
significantly different (p. > 0.05) from the unsprayed. Bt. and neem seed water extract 
(NSWE) treated plots for all three seasons (Table 3.7).
64
Table 3.7 Mean Percentage Parasitism of P. xylostella by C. plutellae on
Different Treatments in the Three Seasons
% Parasitism
Treatment Major Rainy Season Minor Rainy Season Dry Season
Unsprayed 68.6 ± 12.9a* 9.9 ± 7.1a** 43.7 ± 8.9a*
Bt 78.3 ± 12.1a 60.6 ± 4.2a
Karate 81.3 ± 4.1a 11.1 ± 6.6a 61.3 ± 4.1a
NSWE - 3.3 ± 3.3a 50.3 ± 8.8a
Means with the same letters in the same columns are not significantly different at the 
5% confidence level. Duncan’s Multiple Range Test.
♦Means in the same row with different number of asterisks as superscripts are 
significantly different at the 5% confidence level (Duncan’s Multiple Range Test).
33.9 Parasitism of T ni by C. plutellae and E. laphygmae in the Major Rainy Season
Mean percentage parasitism of T. ni by C. plutellae and E. laphygmae during the 
major rainy season was 29.4% ± 7.5.
33.10 Parasitism of T. ni by C  plutellae and E. laphygmae on Insecticide Treated Plots
There was no significant difference (P > 0.05) in parasitism of T ni by C. plutellae and 
E. laphygmae irrespective of treatments (Table 3.8).
Table 3.8 Mean Percentage Parasitism of T. ni by C  plutellae and £
laphygmae on Different Treatments in the Major Rainy Season
Treatment % Parasitism
Unsprayed 29.4 ± 7.5a
Bt 36.7 ± 9.4a
Karate 41.7 ± 20.1a
Means with the same letters in a column are not significantly different at the 5% 
confidence level, (Duncan’s Multiple Range Test).
65
33.11 Emergence of C. plutellae Adults from Field Parasitised Pests
The proportion of C. plutellae adults that emerged from field parasitized P. xylostella 
was not significantly different (p > 0.05) between unsprayed and Karate treated plots 
in all seasons (Table 3.9). In the major rainy season the highest mean percentage 
adult parasitoid emergence was recorded from hosts collected from Bt treated plots. 
The single P. xylostella larva collected from the neem treated plots in the dry season 
emerged, hence, the 100% emergence of parasitoid adults.
Table 3.9 Emergence of C. plutellae Adults Reared from Field Parasitized P. 
xylostella from the Different Treatments in the Three Seasons
Season Unsprayed Karate Bt Neem
Major rainy season 79.17 ± 10.63'*’ 71.64 ± 10.39“* 100±0.00b* -
Minor rainy season 75.00 ±25.00*' 53.35 ± 18.84"* - 100 ±0.00*
Dry season 80.18 ± 10.49"* 65.69 ±6.80“* 70.91±11.25’** 64.57 ±6.04*
Means in the same row with same letters as superscripts are not significantly different 
at 5% confidence level (Duncan’s Multiple Range Test).
'Means in the same column with different number of asterisks as superscripts are 
significantly different at 5% confidence level (Duncan’s Multiple Range Test). Where 
there is no asterisk, data was not included in analysis.
It was also observed that it was only C. plutellae adults recorded from the 
diamondback moth collected from Karate treated plots that died in the process of 
eclosion (could not push the cap of the pupal case), or died the same day, lived for 
only a day or were malformed (twisted wings or twisted abdomens).
With regard to T. ni the highest proportion of adult parasitoids emerged from pest 
samples collected from Bt. treated plots (100%) and unsprayed plots (85.70 ± 6.33) 
and the least (53.96 ± 29.14) from samples collected on Karate treated plots (Figure
66
100
|  80
§> _ 
t  60
f  40S*
20
0
120
Unsprayed Karate Bt
OUBER*BNR
Neem
Figure 3.8: Emergence of both C. plutellae and E. laphygmae Adults from Field
Parasitized T. ni from the Different Treatments in the Major Rainy Season 
Bars with the same letters are not significantly different at the 5% 
confidence level (Duncan’s Multiple Range Test).
33.12 Emergence of C  plutellae Adults Collected as Pupae Exposed to Different 
Insecticides in the Field
Seasonal differences were observed in the abundance and adult emergence from 
parasitoid pupae collected in the field (Figure 3.9 and Appendix 3.2). The highest 
total numbers of parasitoid pupae were collected from the Karate treated plots in both 
seasons. Percentage emergence of parasitoids was significantly higher (p > 0.05) in 
the major rainy season samples than the dry season samples in all treatments (Figure
3.9). In the major rainy season, there was no significant difference (p > 0.05) between 
the rates of adult emergence of parasitoid pupae collected on Karate treated plots and 
the unsprayed plots. There was also no significant difference (p > 0.05) between the 
rates of emergence from samples collected from the Bt and unsprayed plots (Figure
3.9). In the dry season, the rate of emergence in samples collected from all treatments 
was similar.
67
100
90
80
70
60
50
40
30
20
10
0
Unsprayed
m  II li. |. |ii ■  i
Karate Bt
Treatment
Neem
OMajor Rainy Season ■  Dry Season
Figure 3.9: Percentage Emergence of C. plutellae Adults Collected as Pufiae from
the Different Treatments.
Bars of the same colour with different letters are significantly different 
at 5% confidence level (Duncan’s Multiple Range Test). Component 
bars with different number of asterisks are significantly different at 5% 
confidence level (Student’s t-Test).
33.13 Mortality of C  plutellae Adults and Emergence of Pupae Exposed to Insecticides 
in the Laboratory.
The test insecticides differed with respect to the mortality caused to adults and pupae 
of C. plutellae (Figure 3.10). Generally, mortality was higher in the adult parasitoids 
than in the pupae. Of the insecticides tested. Karate had the most adverse effect on 
adults of C. plutellae irrespective of application method. It resulted in 100% 
mortality of C. plutellae within ten seconds of direct exposure.
68
■Karate
■Bt
□Neemazal
Key: FP= Filter paper CL=Cabbage leaf dip S = Spray
Figure 3.10: Mortality of Adults and Pupae of C. plutellae Exposed to Different
Insecticides.
Bars of the same colour with different letter are significantly different 
at the 5% confidence level (Duncan’s Multiple Range Test).
Neemazal had the least adverse effect on the adults after 48 hours. Bt. at 1.0 g/iitre 
and Neemazal at 1% caused a significantly higher mortality in the pupae than in the 
adults. The application methods of the insecticides had variable effects on both the 
adults and pupae of the parasitoid. A significantly higher mortality of 31% (p < 0.05) 
was recorded in the pupae exposed directly to Neem Azal as spray whereas Karate 
caused only 3.6% after 48 hours.
Discussion
The Lepidopteran species found on cabbage in Ghana were similar to species 
recorded in some countries (Talekar, 1992; Anene and Dike, 1996; Dobson et al, 
2002). However, other pests such as Pieris rapae (Linnaeus) (Oatman and Platner. 
1969) and Crocidolomia binotalis (Zeller) (Sastrosiswojo and Setiawati, 1992)
recorded elsewhere in South East Asia were not observed in the present study. 
Forsyth (1966) however, reported C. binotalis on cabbage in Aburi and Tafo both in 
the Eastern region of Ghana.
Plutella xylostella is considered as a serious pest worldwide and occurs in significant 
numbers in parts of South East Asia (Talekar, 1992) but in France, Germany and 
South Africa it is ranked substantially low (Lim, 1986; Mosiane, et al., 2003). 
Results of this study have shown that it occurred in abundance on cabbage in areas 
where the crop had been traditionally grown for at least 10 years in Ghana. However, 
contrary to reports by Tadashi et al. (1986), Walunj and Pawar (2004) and (Pratissoli) 
et al. (2008) that P. xylostella occurs wherever cabbage is grown, the field surveys 
carried out during this study, showed that the pest had not yet invaded some areas in 
the Greater Accra region where farmers were introduced to grow cabbage for the first 
time under the Agro-skills Development and Farmer Field Schools Programme of the 
FAO/UNDP National Poverty Reduction Programme in (1999 - 2001). In these areas 
where cabbage had been recently introduced, the cabbage flea beetle, Phyllotreta 
cheiranthei and Hellula undalis were present. Plutella xylostella was also not present 
in villages located near the Homasi concession of Anglogold Ashanti Ghana Ltd. in 
the Amansie Central District in the Ashanti Region.
Spoladea recurvalis is not considered a pest of cabbage as it was more associated with 
the weed, Cyperus rotundus. Its population was only 1.1% of the total Lepidoptera 
pests in an annual production of cabbage at the experimental site and may have 
moved onto the crop from the weeds. Adults were usually observed resting on weeds 
rather than on the cabbage.
70
This study has demonstrated, for the first time, the seasonality of the major 
Lepidopteran pests in Ghana. Trichoplusia ni was more abundant than P. xylostella in 
the major rainy season but the latter was present in significant numbers throughout the 
year and may therefore, cause more damage in an annual production of three seasons. 
Plulella xylostella consumes more foliage than T. ni in an annual production of 
cabbage despite the voracious feeding habit of T. ni (Harcourt et al., 1955; Capinera, 
1999). It overshadows T. ni because of its ability to quickly develop resistance to 
virtually all insecticides used to control it (Hill and Foster, 2000). It is the most 
important of the crucifer pests and causes severe economic damage to cabbage 
(Sarfraz et al; 2005). The continuous presence of this pest on the same plants that 
were sampled weekly throughout the study period also suggests that there may be as 
many as 20 generations per year. Keinmeesuke et al. (1992) and Abdel-Razek et al. 
(2006) reckoned that as many as 20 - 25 generations can occur in a year in the tropics. 
There were several instances when whole crops were lost to Plulella xylostella at the 
experimental site and farmers had to prematurely harvest their cabbage or abandon 
their farms because of the pest (Cobblah, 2000). Attention must be paid to 
Trichoplusia ni during the major rainy season, having constituted 79% of the total 
pest population during the period of this study. This would be in agreement with 
observation by Anene and Dike (1996) who observed that in Nigeria, the population 
of T. ni can reach epidemic levels. Hellula undalis constituted only 1.4% of the total 
pests, and was only present during the minor rainy season and dry season. The pest is 
known to cause extensive damage to cabbage seedlings in the nursery as well as 
young plants in the field (Muniappan and Marutani, 1992; Jayma and Ronald, 2007). 
It has been reported as a major pest of cabbage in Ghana (Obeng-Ofori et al.. 2007). 
Spodoptera littoralis has not been recorded on cabbage in Ghana before and may be
71
considered seasonal as it occurred in significant numbers only in the minor rainy 
season during the study. Helicoverpa armigera accounted for 2.6% of the pest 
population throughout the study. Various Spodoptera species, as well as Helicoverpa 
armigera are considered occasional or seasonal pests on cabbage in various countries 
(Boling and Pitre. 1971; Waterhouse. 1992; Poelking, 1992; Berg and Cock, 2000).
Findings from the present study also indicate that the incidence and importance of a 
particular species and. its seasonal trends may vary from place to place and with time 
of planting as observed by Dennill and Pretorius (1995) and Mosiane et al. (2003). 
Ooi (1986) and Alam (1992) noted that dry season or warm weather favours the build­
up of P. xylostella. This observation has been confirmed in the present study with the 
populations of P. xylostella significantly higher during the dry season than in the 
major rainy season when T. ni was more abundant. Conversely, Nagarkatti and 
Jayanth (1982) observed a significantly higher build-up of P. xylostella during the 
rainy season compared with other seasons.
Of the fifteen species of parasitoids and hyperparasitoids recorded from the pests. 
Cotesia plutellae was the most dominant parasitoid and was active in all the three 
seasons at the experimental site. It accounted for over 90% parasitism of the 
diamondback moth as have been observed in parts of China by Liu et al. (2000) and 
in South Africa by Mosiane et al. (2003). It comprised 60.9% of parasitism of T. ni. 
Apart from C. plutellae, about 30 species of Chalcidoidca have been recorded in the 
literature as primary parasitoids or hyperparasitoids of P. xylostella (Fitton and 
Walker, 1992). The authors, however, believe that most of these may well be 
hyperparasitoids identified from rather dubious, single, casual rearings and, therefore.
72
require confirmation from further studies. Of the six species recorded in the present 
study, and which are also included in the above previous records, only Elasmus sp 
was obtained from a single rearing. The present study has, therefore, confirmed five 
species as credible records at least in Ghana. The other five species were both 
parasitoids and hyperparasitoids. Of these, O. sokolowskii, the commonest 
hyperparasitoid obtained in this study, had been reported as indigenous to various 
Islands in the West Indies, occurring wherever cabbage was grown (Alam, 1992).
Euplecirus laphygmae was the second most important parasitoid of T. ni having 
accounted for 35.5% of its parasitism. Parasitoids of the pest are however, not 
considered key mortality factors (Oatman and Platner (1969) cited in Capinera, 2008). 
The six species of parasitoids recorded from S. littoralis caused only 8% parasitism 
during the study period. When C. plutellae occurred together with Euplectrus 
laphygmae, a gregarious parasitoid which was found in this study to be restricted to 
Trichoplusia ni and Spodoptera littoralis, it caused a higher rate of parasitism in T. ni 
than did E. laphygmae. Only a single Hellula undalis was parasitized by C. plutellae 
during the study. However, in Malaysia, Sivapragasam and Chua (1997) reared a 
braconid. Bassus sp. and an ichneumonid Trathala flavoorbitalis (Cameron) from the 
larvae on cabbage. The authors nevertheless, noted that these parasitoids were not 
important mortality factors of the pest as they were present only at the end of the 
season and also in very low numbers.
Apart from the effects of parasitoids, the low incidence of P. xylostella in the major 
rainy season could also be attributed to the rains washing off the relatively small 
larvae. There were many instances in the present study when several larvae of
73
Plulella xylostella were observed drowned in water on the lower leaves of the 
cabbage plant after rains. In addition, during heavy rains on three occasions in the 
major rainy season (June), not a single P. xylostella larva was recorded on plants 
which were sampled after the rains. This seasonality can be exploited in the timing of 
planting to avoid heavy infestation and also to reduce irrigation costs. The drowning 
effect of rain on P. xylostella has been simulated in Asia where sprinkler irrigation 
systems in experiments considerably reduced pest numbers (Nakahara et al., 1986; 
Tabashnik and Mau, 1996).
Wide variations in parasitism levels by C. plutellae had been recorded from locality to 
locality, season to season, and from country to country, even in areas with similar 
climates (Jayarathnam, 1977; Ooi and Chua, 1986; Hu et al., 1997; Rowell et al..
2005). It had also been observed that parasitism levels by this parasitoid could not 
exceed 60% (Ooi, 1979 a & b; Ooi. 1992). In the present study, mean parasitism rate 
recorded was significantly higher in the major rainy season (68.6 ± 12.9%) than in the 
minor rainy season (9.9 ± 7.1%). Seasonal variations of parasitism by this parasitoid 
were also noted by Yadav et al. (1974) but he on the contrary, observed that the rains 
reduced percentage parasitism. In China Liu et al. (2000) recorded 10 - 60% whilst in 
Thailand Rowell et al. (2005) recorded between 14 - 78%. In addition, the combined 
mean parasitism of 29.4 ± 7.5% caused by C. plutellae and £. laphygmae to T. ni in 
the major rainy season suggests the need to conserve these parasitoids. They are 
unquestionably valuable agents for biological control of P. xylostella and T. ni on 
cabbage in Ghana.
74
The relationship between diamondback moth and C. plutellae, was observed to be a 
clear and distinct density dependent one, with a positive correlation between them in 
all the three seasons in the present study. Cock (1985) also made similar observations 
and observed that rates of parasitism by C. plutellae was between 89 - 100% in the 
Carribean, whilst Alam (1992) noted that parasitism rates could go up to 100% in 
Jamaica. The least correlation of 0.55 and the highest of 0.97 were observed in the 
minor rainy season and major rainy season respectively. The initial time lag between 
the parasitoid and its host in the present study during the minor rainy season and the 
major rainy season could be attributed to the very low infestation levels of the 
diamondback moth early in the crop season. Hu et al. (1997) and Mitchell et al. 
(1997b) considered this parasitoid inefficient because of its poor searching ability 
when pest populations were low. Ooi (1986) and Ooi (1992) also contended that in 
Malaysia, this parasitoid could not prevent diamondback moth numbers from rising in 
the dry season when pest populations were high. Among the reasons advanced for the 
inability of C. plutellae to increase with increasing pest numbers are the lack of 
understanding of its biology (Fitton and Walker, 1992) or the consequences of 
environmental factors such as temperature and humidity (Loke et al.. 1992). 
However, Ingham and Kfir (1997) indicated that in South Africa this parasitoid was 
effective when diamondback moth populations were high. Contrary to the 
observation by Ooi (1992), in the present study, C. plutellae caused a mean parasitism 
of 43.7 ± 8.9% of P. xylostella with a coefficient correlation of 0.66 during the dry 
season when pest populations were highest. Notwithstanding these contrasting 
observations, the presence of C. plutellae in all three seasons and its ability to increase 
with increasing pest numbers make it a good candidate for biological control of the
75
major Lepidopteran pest, P. xylostella as well as T. ni in the cabbage ecosystem in 
Ghana.
The ineffectiveness of C. plutellae in keeping diamondback moth populations down in 
some countries had also been attributed to activities of hyperparasitoids (Moral lo- 
Rejesus and Sayaboc, 1992). The negative effect of hyperparasitoids had however, 
been refuted by other workers who argued that they are of little significance and of no 
economic impact (Robertson, 1939; Mustata, 1992). In the present study, the total 
composition of the four hyperparasitoid species was less than 8.0% and was mainly 
the facultative species O. sokolowskii.
The high parasitism rates caused by C. plutellae to diamondback moth on karate- 
treated plots at Weija, provide some support to the findings by Ooi (1992) that, this 
parasitoid has developed resistance or is tolerant to insecticides in the field. Furlong 
et al. (1994) noted that C. plutellae was more tolerant to pyrethroids than other 
parasitoids of P. xylostella. Loke et al. (1992) observed a mean parasitism of 48.6% 
whilst Liu et al. (2000) recorded substantia) rates of parasitism even under very heavy 
insecticide pressure. In the present study, the mean parasitism of 81.3 ± 4.1% 
observed on the Karate treated plots in the major rainy season and 61.3 ± 4.1% in the 
dry season lend further credence to these observations. Nevertheless, further and 
more direct studies are required to determine the insecticide resistance status of this 
parasitoid on cabbage in Ghana in order to draw firmer conclusions.
The extremely low parasitism of the diamondback moth observed on the farmer’s 
farm could be attributed to the indiscriminate use of the variety of insecticides applied
7 A
from very early in the season. Rowell et al. (1992) noted that, the main ‘gap’ in the 
occurrence and activity of diamondback moth parasitoids appears to be the critical 
period early in the season when farmers are most likely to treat with broad spectrum 
insecticides.
Even though substantial numbers of the parasitoids reared from P. xylostella hosts 
collected from Karate and neem seed water extract treated plots emerged, the 
parasitoids were adversely affected. Neem inhibited or arrested growth and 
development, and prevented the larvae that emerged from field parasitized hosts from 
pupating or spinning cocoon. Even when they spun their cocoon, on dissection, it was 
found that the larva had not undergone structural differentiation. Adult parasitoids 
that emerged from pests collected from Karate treated plots were short lived, living 
for only a day, or dying soon after eclosion or during eclosion. In some cases the thin 
line of weakness along the pupal case from where the adult would emerge was visible 
but they could not emerge and their heads were broken off. There was no significant 
difference between emergence rates of C. plutellae collected as pupae from Karate- 
treated plots (81.3 ± 8.19%) and unsprayed plots (69.10 ± 90%) in the major rainy 
season. This observation may be due to the rains diluting the effects of the 
insecticide.
The results of the laboratory studies on the direct effect of Karate on C. plutellae 
adults is similar to observations made by Condor (2007), who observed that the 
insecticide caused 100% mortality to adult Diadegma mollipla. another important 
parasitoid of P xylostella. The implications of these are that Karate could reduce the
77
effectiveness of C. plutellae by directly eliminating them, or causing a decrease in the 
numbers that will be available to sustain succeeding generations of the parasitoids.
Even though the neem adversely affected development of the parasitoid in this study 
at the concentrations used, there is also evidence that, neem treatments do not affect 
parasitoids and can be compatible with Integrated Pest Management programmes 
when lower doses are used or depending upon the formulations (Charleston et al., 
2005; Haseeb et al., 2006).
Previous studies had shown that certain pesticides were highly toxic to adult C. 
plutellae when sprayed directly at the recommended rates while others showed little 
to no toxicity (Kao and Tzeng, 1992; Perez et al, 1995). The results also indicate that 
the choice of insecticide that could be integrated with C. plutellae for pest 
management on cabbage should be properly understood. Variation in the response of 
C. plutellae to the test insecticides, imply that an effective pest management strategy 
for P. xylostella that would include this parasitoid and chemical control can be 
developed. The results have also contributed in clarifying the relationships that are 
important in the integrated pest management of the diamondback moth and the other 
pests. Integrated pest management programme that is focused on conservation of 
local parasitoids will help alleviate the growing public concern regarding the effects 
of pesticides on vegetable growers and consumers. From the results obtained, an 
integrated pest management strategy based on either the use of lower doses of neem 
seed water extract or Bacillus thuringiemis and Cotesia plutellae, coupled with 
appropriate timing is recommended for the Weija vegetable irrigation company 
WEICO.
78
CHAPTER FOUR
4.0 BIOLOGY AND ECOLOGY OF THE PARASITOIDS OF LEPIDOPTERAN 
PESTS OF CABBAGE
4.1 Introduction
Parasitoids alone, or in combination with other control measures, have been employed
against various cabbage pests with varying degrees of success (Mitchell et al., 1997a,
b; Mahar et al., 2004). They are nevertheless a valuable control component and
resource and. unless the important ones are made a part of any management strategy
against the pests of cabbage, the plague of the major pest, P. xylostella and other
related problems are likely to persist (Clausen, 1978; Lim, 1986; Liu, et al., 2000;
Pratisolli et al.. 2008). Parasitoids provide considerable impact and effective check
on multiplication of the diamondback moth (Lim, 1992; Ooi, 1992; Hamilton et al.,
2004). In some countries, there is direct evidence that the action of parasitoids arrest
or obliterate infestations of P. xylostella or keeps it under control (Ingham and Kfir,
1997). In some instances, reduction in pest population is so marked that the use of
insecticides could become unnecessary (Waterhouse, 1992). Indeed, there are known
cases of successful P. xylostella control in which the basic control component
constituted parasitoids (Lim, 1986; Mustata et al., 2006). However, investigations
into the biology and ecology of the important parasitoids of P. xylostella are limited
(Lim, 1986; Pratisolli et al, 2008). Fitton and Walker (1992) suggested that the
contradictory reports regarding the effectiveness of C. plutellae in reducing the
population of the diamondback on cabbage could be due to a lack of understanding of
the biology of this parasitoid in various countries. On the other hand, contribution of
parasitoids in the control of the other pests on cabbage has not been encouraging or
79
clear (Talekar N. S. 1992; Sivapragasam and Chua, 1997; Capinera, 2008; Jayma and 
Ronald. 2007).
The guild of parasitoids recorded on the diamondback moth is large and varies from 
region to region, though not all of them are effective (Lim, 1986; Mustata el al..
2006). Only a few species of Trichogramma and Trichogrammatoidea have been 
reared from the eggs. These, however, gave satisfactory results and good searching 
ability in the laboratory, but did not show promise in the field (KJemm el al., 1993). 
Nevertheless, Keinmeesuke et al. (1992) observed that Trichogrammatoidea bactrae 
Nagaraja caused parasitism of 16.2 -  45.2% from diamondback moth eggs collected 
from the field.
The greatest control is provided by the larval parasitoid species belonging to the 
Hymenoptera genera, Diadegma, Cotesia and Microplitis (Sarfraz el al., 2005). 
Attention is therefore increasingly being given to their use in controlling the major 
pest of cabbage worldwide. However, in Africa in general, and Ghana in particular, 
the identities and biology of members of the parasitoid complex are either not known 
or are very poorly known (Quicke, 1997; La Salle, CABI Bioscience UK Personal 
communication). Indeed, for any meaningful exploitation of the parasitoids 
associated with either the major pest or the other lepidopterous pests of cabbage in 
Ghana, it is vital that their biology and especially their behaviour in the field are very- 
well understood. Understanding the biology of local populations of parasitoids would 
yield valuable information on host ranges in nature that can also be useful in rearing 
for augmentative releases in biological control.
80
The objective of this study was to determine the biology (life history, lifestyle, 
longevity and host preference) and ecology (searching and oviposition behaviour) of 
the parasitoids of the pests observed in this study, with emphasis on the dominant one 
based on laboratory and field data.
42  Materials and Methods
4,2.1 Field Sampling and Rearing of Host -  Plutella xylostella
Cotesia plutellae was the predominant species observed from the Lepidopteran pests 
and was, therefore further studied in the laboratory in the Department of Zoology’ 
(now Department of Animal Biology and Consercation Science, DABCS) of the 
University of Ghana. In order to study the parasitoid, the host had to be obtained and 
reared. Larvae of P. xylostella were collected from cabbage at the experimental site at 
Weija. The larvae still attached to cabbage leaf were kept in petri dishes lined with 
wet filter paper and brought to the laboratory. Prevailing laboratory conditions were a 
mean temperature of 23 ± 2 °C and relative humidity of 45 ± 1.0%. The larvae were 
individually placed on moist filter paper in petri dishes on the laboratory bench and 
were fed with fresh pieces of cabbage leaf daily and observed till the adult pest 
emerged. Emerging adults were put in mating and oviposition wooden cages 
measuring 45 x 45 x 45 cm and provided with 10% honey solution soaked in cotton 
wool and placed in a petri dish. A small cabbage seedling was placed in a beaker 
containing water and placed inside the cage for oviposition by P. xylostella. The eggs 
that were laid by P. xylostella were harvested still attached to the leaf and incubated in 
a petri dish lined with wet filter paper till hatching. Upon hatching, the newly 
emerged larvae were placed separately in a petri dish and fed with cabbage leaves.
81
4.2.2 Field Collection and Rearing of Parasitoids
Cotesia plutellae pupae that emerged from P. xylostella larvae that had been collected 
in the experimental plots were kept in tubes till emergence of adult parasitoids. In 
addition, parasitoid pupae still attached to pieces of cabbage leaves were carefully 
detached with a pair of forceps and brought to the laboratory. The adult parasitoids 
that emerged were fed on 10% honey solution and allowed to mate in small plastic 
transparent cages (11.0 x 7.0 cm) fitted with gauze for 24 hours before being used for 
the study.
Data for the other parasitoids (Euplectrus laphygmae, Chelonus curvimaculatus, 
Oomyzus sokolowskii. Tetrastichus atriclavus s.L, Aphanogmus reticulatus, Charops 
sp, Brachymeria sp. Hockeria sp, Notanisomorphella sp, Elasmus sp. Pediobius sp, 
Trichomalopsis sp, Blepharella vasta and Peribaea orbata) were taken from the field 
samples as well as in the laboratory where possible. As a result, the numbers of each 
species used varied depending upon availability.
4.23 Life History and Lifestyle Studies of Cotesia plutellae
A male C. plutellae was exposed to a female for 24 hours to allow mating in a 
transparent glass jar (7.0 x 6.0 cm) that had been provided with a streak of 10% honey 
solution and covered with a piece of gauze. The female was then aspirated through a 
slit made in the cover of the rearing jar into another prepared transparent jar (7.0 x 6.0 
cm) containing a three-day old P. xylostella larva reared in the laboratory as described 
above (4.2.1), a piece of cabbage leaf and a streak of 10% honey solution as food for 
the pest and parasitoid respectively. The interaction between the adult female 
parasitoid and the diamondback moth host was observed. After 24 hours, the adult
82
female parasitoid was allowed to escape into a rearing cage and the host larva 
transferred into a petri dish lined with a wet filter paper and provided with a piece of 
cabbage leaf. The larva was observed daily till the parasitoid larva emerged or the 
host pupated. Food for the host was changed every other day till pupation of host or 
emergence of parasitoid larva. It was not possible to determine the egg incubation 
period inside the host so the total egg incubation and larval duration was determined 
for each individual parasitoid. The duration of the pupal period of the parasitoids was 
recorded. The nature of the newly emerged parasitoid larva and its appearance were 
noted. The spinning of the pupal case by the parasitoid larva and the position from 
which the adult parasitoid emerged from the pupal case were also noted. The sex of 
the parasitoid was determined after adult emergence based on the presence or absence 
of an ovipositor. Four replicates each consisting of five adult C. plutellae were used in 
the studies. The data were then pooled and the mean developmental periods 
determined.
4.2.4 Longevity Studies of Cotesia plutellae
To determine the longevity of mated and unmated C. plutellae adults, two 
experiments were set up. In the first experiment, 10 day-old unmated adult male and 
female parasitoids were kept singly in tubes and plugged with absorbent cotton wool. 
Each parasitoid was fed on a streak of 10% honey solution which was replenished 
every third day. In the second set-up, a newly emerged male was exposed to a female 
for 24 hours to allow mating in a transparent glass jar (7.0 x 6.0 cm). They were then 
separated and placed singly in glass tubes plugged with absorbent cotton wool and 
provided with a streak of 10% honey solution as food. Each parasitoid was observed 
daily till it died. The period between the beginning of the experiment and death was
83
recorded as longevity in days for each individual parasitoid. The data were pooled for 
each category and the mean longevity determined.
4J.5 Oviposition Preference of Plutella xylostella Larvae by Cotesia plutellae
In order to determine the preferred diamondback moth host stages by C. plutellae, a 
no-choice experiment was conducted. Twelve newly mated parasitoid females were 
individually exposed to each of 3 day old (2nd instar), 6 day-old (3rd instar) and 8 day 
old (4lh instar) larvae o f the diamondback as described above. After 24 hours, the 
parasitoid was allowed to escape and the host larva transferred into a petri-dish lined 
with a wet filter paper and provided with a piece of cabbage leaf. The larva was 
observed daily and the piece of cabbage changed every other day till the host pupated 
or the parasitoid larva emerged. The number of diamondback moth larvae from 
which parasitoid larvae emerged for each larval instar was pooled and the percentage 
preference calculated.
42.6 Field Observations on Biology and Ecology of the Parasitoids
Field observations were carried out on the seven central plants of the unsprayed plots 
at the experimental site at Weija as the pests were sampled. The part of the plant 
where parasitism of pests occurred in the field was recorded. Searching and 
oviposition behavior of adults in the field were recorded. The number of parasitoids 
that emerged from a host, the developmental stage and the behavior of the parasitoid 
were also recorded. Parasitoid lifestyle was recorded as solitary when only one adult 
emerged from its host and gregarious when more than one adult emerged from its 
host. In addition, where possible the duration of larval and pupal stages of the other 
parasitoids were recorded from field samples of pests described in Sections 3.2.7 and
84
3.2.8 of this thesis. The sex ratios were calculated for each parasitoid species from 
the numbers of male and female adult parasitoids reared from field samples of pests 
but the numbers used varied according to availability. For C. plutellae, the sex ratio 
was calculated from 151 individuals reared from field-collected larvae of the 
diamondback moth
43  Results
43.1 Biology and Ecology of Cotesia plutellae
43.1.1 Life History and Lifestyle of C. plutellae
The duration of the total life cycle of Cotesia plutellae in the laboratory at an average 
temperature o f 23 °C ± 2 and relative humidity of 45 % ± 1 was similar for males and 
females. It averaged 16.0 ± 0.5 days and 16.1 ± 03 days for males and females, 
respectively. The egg incubation plus larval developmental period averaged 9.1 ± 0.4 
days for males and 9.1 ± 0.2 days for females. Pupal period was 6.9 ± 0.3 days and
7.1 ± 0.3 days for males and females, respectively.
The adult parasitoids mated on the same day that they emerged. During courtship, the 
males intensively fanned their wings around the females as they attempted to mount 
them.
Cotesia plutellae behaves as a solitary endoparasitoid and lays one egg per host. 
Thus, only one adult emerges from a parasitized host. The adult C. plutellae, after 
laying her egg in the larval host exhibited koinobiosis, allowing the host larva to feed 
and develop for some time. The final larval instar of the parasitoid emerged after
about 9 days and immediately began spinning a creamish to off white cocoon whilst
remaining very close to the host, most probably soliciting the needed physical support
85
from its host (Plate 4.1). The newly emerged final larval instar of C. plutellae was 
translucent, yellowish green and slightly curved. It usually emerged from the 
posterior part of the host near the proleg and stayed close to the host. The sclerotised 
mandibles of the parasitoid larva were distinctly visible as it spun the cocoon. Within 
24 hours, it pupated on the leaf surface near the host (Plate 4.2). The pupa was firmly 
attached to the leaf surface. The newly formed cocoon was slightly rough and 
appeared as a thin net-like cover around the pupa. By this time the host had stopped 
feeding and looked pale. It became deformed as a result of the parasitoid exit hole 
and assumed a characteristic more or less ‘C’ shape (Plate 4.2) but was still capable of 
some movements. The unparasitised diamondback moth larva maintains its spindle 
shape (Plate 4.3).
Plate 4.1: Newly emerged C. plutellae Plate 4.2: C. plutellae
larva (arrowed) and host pupa (arrowed) and host
Plate 4.3: Unparasitised |»|atl. 4.4 : Empty pupa| cocoon
P. xylostella larva |xlO| of c. plutellae (arrowed)
86
At the end of the pupal period, the cocoon opened at one end through which the adult 
parasitoid emerged (Fig. 4.4). Sometimes the cap remained attached or it was 
completely detached from the rest of the pupal case. By the time the adult parasitoid 
eclosed, the host carcass had dried up (Plates 4.4 and 4.5).
Plate 4.5: Carcass of P. xylostella after parasitism
.3.1.2 Longevity of Mated and Unmated Adnlt Cotesia plutellae
Mated and unmated females lived for an average of 13.7 ± 1.1 days and 7.7 ± 0.6 
days, respectively. On the other hand, mated and unmated males lived for an average 
of 15.8 ± 1.5 days and 7.0 ± 0.6 days respectively.
3 .1 3  Oviposition Preference of Plutella xylostella Larvae by Cotesia plutellae
In the no-choice experiments, adult Cotesia plutellae attacked 2nd instar (3 day-old), 
3rd instar (6 day-old) and 4lh instar (8 day-old) larvae of Plutella xylostella, but with a 
preference for second and third instar larvae. Eighty percent (10/12) and 50% (6/12) 
of second and third instar larvae of the diamondback moth were parasitized, 
respectively as opposed to 33% (4/12) of the fourth instar larvae.
87
When presented with the large hosts (i.e 3rd - 4th instars), the parasitoid had more 
difficulty inserting her ovipositor to lay eggs. The host always put up a defensive 
behaviour, vigorously wriggling around the parasitoid and either dropping via a silken 
thread, or dislodging the parasitoid. Sometimes, the host flipped off the parasitoid so 
vigorously that it hit one side of the glass tube. After such an encounter the parasitoid 
always spent some time cleaning itself after which it made another attempt.,
1.3.1.4 Field Observations on Parasitism by C. plutellae
Cotesia plutellae normally parasitises the second or third instar larvae of the various 
Lepidopteran pests of cabbage, namely; Plutella xylostella, Trichoplusia ni, 
Spodoptera littoralis and Hellula undalis in the field. C. plutellae is, therefore, not 
strictly host specific though the results obtained from the field indicated that it 
preferred P. xylostella. In the field, the emerging parasitoid larva always laid very 
close to its host as was observed in the laboratory and pupation usually occurred on 
the ventral surface of the leaf. As the pupa aged, the thin cocoon which covered it 
was sometimes lost or washed off after rains. The pupae of C. plutellae emerging 
from P. xylostella were smaller than those from T. ni and they had an average length 
of 3.05 ± 0.01 mm (N = 20) compared to an average of 3.64 ± 0.06 (N = 20) mm for 
T. ni.
Cotesia plutellae was sometimes observed to attack older larvae of T. ni in the field, 
but the host was not killed and continued to develop till the parasitoid emerged after 
which the adult moth also emerged. In such cases, the emergence hole could still be 
seen on the host larva obviously not having been adversely affected. For example, 
five adults of C. plutellae emerged from three 3rd and two 5lh instar larvae of T. ni
88
which later pupated and normal adult moths also emerged. Large larvae of T. ni were 
observed to be exceptionally defensive when the parasitoid attempted to oviposit in 
them. In the cases when C. plutellae parasitised larvae of S. littoralis and H. undalis, 
the adult parasitoid failed to emerge from its pupa. On the two occasions that 
multiple parasitism of Cotesia plutellae, Euplectrus laphygmae and another 
unidentified gregarious parasitoid was observed, C. plutellae out-competed them, with 
the adults emerging whilst the other species died. When both C. plutellae and £. 
laphygmae parasitised T ni larva the former species emerged, with only a few of the 
latter emerging.
As the crop matured and was ready for harvest, it was common to see a number of 
parasitised hosts, parasitoid pupae and newly emerged parasitoid larvae close by the 
hosts together on one leaf. Adult parasitoids were often observed in the field 
systematically and vigorously tapping their antennae and ovipositor along the cabbage 
leaf surfaces from the edges, obviously searching for hosts. This was particularly 
common when Plutella xylostella populations were low. When the crop had matured, 
several of the parasitoids were observed hovering above the plant.
The sex ratio was slightly higher for males than for females. Field collected samples 
gave a sex ratio ratio of 1: 1.06 (73 females: 78 males).
89
43 2  Biology and Ecology of Other Parasitoids 
Charops sp (Ichneumonidac)
This was found to be a solitary parasitoid of late larval instar of Trichoplusia ni and 
Spodoptera littoralis. It was in turn parasitised by a Brachymeria sp and was present 
during the dry and minor rainy seasons from October to March. The larva (N = 2) 
that emerged from field parasitized host was amorphous in shape, pale brown (off 
white) and was very soft and flexible. It pupated within an hour or two after 
emergence from the host. It formed a brown oval shaped pupal case which had a ring 
of conspicuous black spots close to either ends of the pupal case (Plate 4.6). The 
pupal case measured between 6.0 - 6.9 mm long in females and 5.2 - 5.5 mm in males. 
The ends were slightly flattened and in the field, it hanged on the ventral side of the 
leaf by means o f a strong silken thread (Plate. 4.6). The pupal period ranged from 6 - 
9 days in females with an average of 6.5 days. The male pupal period lasted seven 
days for each of a sample of five pupae. The adult parasitoid emerged through the 
sub-dorsal side of the case above the ring of black spots (Plate 4.6).
90
Chelonus curvimaculatus (Ichnenmonidae)
This species was observed to be a solitary parasitoid of larvae of Spodoptera littoralis. 
Only two males were recorded in the minor rainy season.
Brachymeria sp (Chalcididae)
A species of Brachymeria was recorded as both a primary solitary parasitoid of pupa 
(N = 5) of T. ni and a secondary parasitoid of T. ni via Charops sp. Specimens that 
were reared as hyperparasitoids from T. ni via Charops sp were smaller measuring 
between 3.0 - 3.2 mm long compared to those that acted as primary parasitoids which 
measured between 5.4 - 5.6 mm long.
91
Hockeria sp (Chalcididae)
A species of Hockeria was recorded only on two occasions from the diamondback 
moth larvae. It was a gregarious parasitoid with a male to female sex ratio of 1:1.5 (N 
=  10).
Elasmus sp. (Elasmidae)
This was observed as a gregarious hyperparasitoid of diamondback moth larva via 
Cotesia plutellae. The adults emerged from the lateral side of the parasitoid pupa It 
was recorded only once (N = 4) during the dry season in March when the cabbage was 
ready for harvesting.
Euplectrus laphygmae (Eulophidae)
These were active gregarious koinobiont ectoparasitoids of third to fourth larval 
instars of T. ni and S. littoralis. When E. laphygmae attempted to oviposit in the host 
caterpillar it flipped off the parasitoid with its abdomen. The adult parasitoid always 
persisted until the ovipositor was successfully inserted after which the caterpillar did 
not attempt to flip it off but continued to struggle till the parasitoid left. The female 
laid more than one egg in a host. The newly hatched parasitoid larvae were small 
green, round to oval bodies with thin pale transverse bands on the body. They 
partially buried themselves in the host and fed on the tissues from the outside (Plate 
4.7). The mature larvae formed aggregations on the dorsal surface of the host, usually 
around the middle patch from where they all fed (Plate 4.8). The larvae when 
matured were barrel or spindle shaped and fully emerged from the caterpillar host. 
Unlike the unparasitised T. ni caterpillar which was bright green, the host at this time 
became very pale, sluggish and stopped feeding (Plate 4.8). The parasitoid larvae
92
later turned slightly pale and migrated to align themselves along the entire ventral 
surface of the host and pupated within twenty-four hours (Plate 4.9).
Plate 4.7: Newly hatched larvae of E. 
laphygmae [x 2.7] (arrowed) 
penetrating host to feed
Plate 4.8: Larvae of E. laphygmae 
(arrowed) about to m igrate to 
pupate
Plate 4.9: Mature larva of E. laphygmae 
migrating (arrowed) down the host to pupate
93
Each larva spun a loose cocoon within which it pupated such that each remained 
separated from the other. A secretion fixed the cocoons to the host and also to the 
substrate (cabbage leaf) which rendered it difficult to dislodge. By this time, the host 
was a dead dark brown flattened carcass with remnants of the cocoons (Plate 4.10).
Plate 4.10: Carcass of T. ni larva after parasitism 
by E. laphygmae
The pupal period varied ranging from 4 to 13 days depending upon temperature in the 
laboratory which ranged from 22.5 - 28 °C. The progeny size per host varied from 2 - 
17 individuals depending upon the size of the host and was sex biased towards 
females. The mean ratio of males to females recorded from field parasitism of T. ni: 
was 1.0:6.5 (N = 45). Size variation was observed in adults of E. laphygmae 
depending on the number emerging from a particular host. Larger hosts ranging in 
length from 16 - 20  mm had more progeny (7 - 13) than smaller ones less than 10 
mm. Where 2 - 3  individuals emerged from large hosts, they were bigger in size. 
Where progeny size was large (15 - 17) a mixture of small and big females were 
observed. Where progeny size was not more than four (N = 5), only females were 
produced. In four instances a male each emerged from fourth instar larva of T. ni.
94
Notanisomorphella sp. (Eulophidae)
A solitary parasitoid species of Notanisomorphella (N = 2) was reared from third 
instar caterpillar of Spodoptera littoralis and were both males. It was recorded at 
Weija during the dry season when the cabbage was cupping. The larva that emerged 
from the host in the laboratory was soft, pinkish, and apodous. PrcpupaJ period was 
three days during which the integument hardened to form a pupa The pupa was 
creamish, exarate and did not spin a cocoon. The two brown eyes were clearly 
visible. Antennae and legs became visible after three days, after which the adult 
emerged the following day giving a pupal period of four days.
Oomyzus sokolowskii (Eulophidae)
This was both a gregarious larval-pupal parasitoid of Plulella xylostella and a 
hyperparasitoid of the same host larva via Cotesia plutellae in the rainy season (April 
and May). The parasitoid emerged from the diamondback moth larvae that had been 
parasitized by C. plutellae as well as pupae of the diamondback moth that was 
collected as larvae from the field. At three different temperatures and relative 
humidity conditions of 25 °C and 70%, 22 °C and 45%, 20 °C and 37% in the 
laboratory, the pupal periods of field parasitized larvae were 11 (N = 6), 19 (N = 11) 
and 21 (N = 5) days respectively. The adults emerged through a small opening in the 
middle of the dorsal surface of the host. The size of the progeny when it behaved as a 
parasitoid was greater than when as a hyperparasitoid. Ratio of male to female from 
diamondback moth pupae (N = 24) was 1:11 and from C. plutellae (N = 17) was 
1:4.7.
95
Tetrastichus atriclavus W aterston s.l. (Eulophidac)
This was a gregarious primary parasitoid of both Trichoplusia ni larva and a 
secondary parasitoid via Cotesia plutellae. The adults (N = 13) emerged through a 
small opening in the center of the dorsal surface of the host.
Pediobius sp. (Euiophidae)
A gregarious species of Pediobius was recorded as a parasitoid of the diamondback 
moth larvae and pupae (N = 4) in the major rainy season (May - June).
Trichomalopsis sp. (Pteromalidae)
This was a primary solitary parasitoid and a hyperparasitoid of the diamondback moth 
via C. plutellae. The adult was not active and emerged by a small opening on the sub- 
dorsal side towards the apex of the cocoon (N = 35). This species was observed in the 
major rainy season from July to August.
Aphanogmus reticulatus (Fouts) (Ceraphronidae)
This is a gregarious endoparasitoid and hyperparasitoid of the pupa of Plutella 
ylostella via C. plutellae (N = 33) in the major rainy season. It was not active and 
flew for short distances giving the impression of hopping. Emergence hole of the 
adult was around the middle portion of the pupal cocoon. The number of individuals 
emerging per host was 3 - 11 and was female biased. Ratio of males to females was 
1:9.8.
Blepharella sp. near vasta (Karsch) (Tachinidae)
This species is a Koinobiont larval-pupal endoparasitoid which attacked late larval 
instars of Spodoptera littoralis. For a period of three days before pupation, the host 
larva became quiescent and shortened and its cuticle became brown and crinkled after 
which it pupated. The parasitoid continued to develop within the pupa of S. littoralis 
from which it emerged as a solitary species (N = 2) (Plate 4.11).
Plate 4.11: Adult B. sp. nr. vasta |x 2.5) and pupal 
case of S. littoralis from which it had emerged
Peribaea orbata (Wiedemann) (Tachinidae)
This species was collected during the minor rainy season from October to December 
when the cabbage had headed. It is a gregarious parasitoid of the larvae of S. 
littoralis. The parasitoid larvae (N = 29) fed within the host larva and reduced it to a 
slightly liquid mass of tissue and later emerged as pale maggots by which time the 
host was dead. They then continued to feed externally on the mass of liquefying 
tissue for 3 - 4 days after which they pupated in small dark reddish puparia (Plate 
4.12). The pupal period lasted for 6 to 11 days at 26 °C in the laboratory. Five to 
eleven adults emerged from a single host. The adult parasitoid emerged from the 
puparium through a neatly cut opening or a rugged opening.
97
Plate 4.12: Adult P. orbata [x 14) and its pupal case
Discussion
The most abundant and important primary parasitoid of P. xylostella and T. ni 
recorded in this study is Cotesia plutellae. It is one of the three most important 
species recorded elsewhere in Asia, parts of Africa and Central Europe (Waladde et 
ai. 1997; Anene and Dike, 1996; Mitchell et al., 1997 a & b; Ingham and Kfir 1997). 
The mean total developmental period of 16.1 days of the parasitoid suggests that it 
may take at least, this length of time before the first adults would emerge from the 
eggs laid by the first females to arrive on cabbage, by which time pest numbers would 
have increased.
It has usually been assumed that Cotesia plutellae is host specific to P. xylostella 
(Talekar and Griggs, 1986; Talekar, 1992; Fitton and Walker, 1992). However, Fitton 
and Walker (1992) have compiled from the literature twenty Lepidopteran host 
species, but questioned the identity of most of these records, and suggested the need 
for a critical appraisal of host specificity. The results obtained from this study
indicated that, at least in southern Ghana, C. plutellae is not host specific. It was 
observed to parasitize four other Lepidopteran pests on cabbage, i.e. Trichoplusia ni, 
Spodoptera littoralis and Hellula undalis but it, undoubtedly, showed a preference for 
P xylostella.
Contrary to observations in parts of South East Asia (Talekar, 1992), in the present 
study, none of the first larval instars of P. xylostella collected from the field was 
parasitized by C. plutellae. This parasitoid may also be adapted to specific host size 
and therefore likely to shift to any other hosts which fall within that size range in the 
absence of adequate numbers of P. xylostella. It was observed that large host larvae 
of T. ni and P. xylostella were more defensive than smaller ones and always 
vigorously flipped them off when this parasitoid tried to oviposit. Baur and Yeargan 
(1994) and Brodeur et al. (1996) also recorded that defensive behaviour increased 
with host age of caterpillars. Kawaguchi and Tanaka (1999) and Shi et al. (2002) 
concluded that parasitism by C. plutellae decreased sharply with increasing host age 
in the fourth instar and approached zero in host larvae that had gone beyond 37% of 
the fourth stadium. This suggests that the acceptance phase might be used as a 
reliable indicator of its host specificity to P. xylostella and younger stages of T ni.
The fact that C. plutellae was not restricted to P. xylostella is not expected to have 
negative implications on its use for biological control of P. xylostella as it has a 
preference for it. It was also able to out-compete other parasitoids including £. 
laphygmae when there was multiple parasitism. Fitton and Walker (1992) have 
suggested that records of species of the Braconid genus Chelonus, as parasitoids of 
the diamondback moth should be treated as doubtfully correct. The present study has
99
however, confirmed that in Ghana, Chelonus curvimaculatus Cameron does not 
parasitise P. xylostella instead, it parasitised S. littoralis. Quartey (1975) referred to a 
species of Chelonus parasitizing a stem borer species in Eastern Ghana, but it has not 
been possible to recover this specimen for examination and comparison with the 
specimen observed on cabbage in the present study. This is the first time a parasitoid 
species belonging to the genus, Chelonus has been recorded from S. littoralis on 
cabbage in Ghana
Charops species have been reared from rice stem borers and Acraea terpsicore L. in 
various parts of Ghana such as Goaso, Kumasi, Atwoabo and Tokwabo (Forsyth, 
(1966; Duodu and Lawson, 1983), but the observation of a new Charops sp as a 
parasitoid of T. ni and S. littoralis in Ghana is a first record.
Species of Brachymeria had been recorded as parasitoids mainly from pupae of 
Lepidoptera, a few Coleoptera, Hymenoptera and Diptera. Boucek (1988) noted that 
some species are obligatory or occasional hyperparasitoids but others are known to be 
solely primary parasitoids. Members of this genus can act as both parasitoids and 
hyperparasitoids as shown in this study and earlier observed by Boucek (1988) and 
Ganeshan et al. (1997).
Several species of Hockeria are known to parasitise pupae of small to medium sized 
Lepidoptera, some of which are Totricidae, Pyralidae and Yponomeutidae (Boucek 
1988), (La Salle, pers. comm.). The present record from the diamondback moth 
pupae on cabbage has added to the list of recognized hosts.
100
Elasmus species had been recorded as hyperparasitioids of the diamondback moth by 
Fitton and Walker (1992). This is the first record of this hyperparasitoid of the 
diamondback moth via C. plutellae on cabbage and in Ghana.
Euplectrus laphygmae is widely distributed in Africa, and had been recorded mainly 
from species of Plusia Latreille and S. littoralis, all in the family Noctuidae (Ferriere, 
1941; 1947; Boucek, 1988; Ganeshan et al., 1997). However, this is the first record 
of £  laphygmae in Ghana and also as a parasitoid of T. ni on cabbage. Zhu and 
Huang (2003) did not list Ghana among the African countries with records of this 
species in their study of the Genus Euplectrus.
Notanisomorphella species had been recorded as parasitoids of small leaf mining 
insects (Lepidoptera and Hispine beetles). One species had been recorded from spider 
egg sacs, possibly as a hyperparasitoid (Boucek, 1988). Various species had been 
recorded in Southern Europe, throughout Africa and warmer parts of Asia and 
Australia It is recorded here in Ghana for the first time as a solitary parasitoid of 
young larvae of S. littoralis.
The status of O. sokolowskii in the trophic system of cabbage appears to be 
controversial. It had been recorded as parasitoids, mainly of Coleoptera (Boucek, 
1988) and as hyperparasitoids of the diamondback moth (Chelliah and Srinivasan, 
1986; Mahmood et al., 2004). Wakisaka et al. (1991) (cited in Talekar and Hu, 1996) 
had also observed that (). sokolowskii was a pupal parasitoid of the diamondback 
moth. Talekar and Hu (1996) showed that in the laboratory, (). sokolowskii failed to 
parasitise pupae of the diamondback moth and argued that it was a larval parasitoid.
In the present study, however, this parasitoid was reared from both field collected 
diamondback moth larvae that had been parasitized by C. plutellae, as well as from 
field collected diamondback moth larvae that later pupated in the laboratory. These 
suggest that it acted as a hyperparasitoid of the diamondback larvae via C. plutellae as 
well as a larval-pupal parasitoid of the diamondback moth. . 2006).
Tetrastichus atriclavus s. L had been recorded in this study as a primary and a 
hyperparasitoid of T. ni via C. plutellae. They had also been observed from pupae of 
Lepidoptera and sometimes, as hyperparasitoids (Boucek, 1988) as observed in this 
study.
Elsewhere, species of Pediobius had been recorded as primary or secondary 
parasitoids of eggs, pupae and sometimes larvae of Lepidoptera, Coleoptera, Diptera, 
Hymenoptera and a few others, including spider egg masses (Burks, 1966). Forsyth 
(1966). in his book on the agricultural insects of Ghana, made no record of Pediobius 
species. The observation of a Pediobius sp as a parasitoid of the diamondback moth 
larvae and pupae on cabbage appears to be a first record in Ghana.
Graham (1969) indicated that, the typical hosts of Trichomalopsis species are pupae 
of Coleoptera and Lepidoptera. In the present study, they were reared as primary 
parasitoids and hyperparasitoids of the diamondback moth larvae via C. plutellae.
This is the first time A. reticulatus has been recorded as a hyperparasitoid of Cotesia 
plutellae via P. xylostella on cabbage in Ghana. The species is a widespread 
indigenous African species, hyperparasitic on lepidopteran hosts via Apanteles sp. and
102
Cotesia sesamia (Cameron) (Polaszek and La Salle, 1995). The authors reared A. 
fijiensis (Ferriere) from stem borers in Ghana. The species was also recorded as a 
hyperparasitoid of C. plutellae in Barbados by Cock (1985).
Peribaea orbata parasitized only Spodoptera littoralis in Ghana. It is known to be a 
common African species and parasitizes various species of Noctuidae including 
Helicoverpa and Spodoptera spp. (pers. com. N. Wyatt, British Museum Natural 
History).
Blepharella sp. near vasta is also restricted to S. littoralis. The species probably 
parasitizes lepidopterous larvae, as do other members of this genus (pers. com. N. 
Wyatt, British Museum Natural History).
For the first time in Ghana, this study has provided and illustrated the guild and 
complex of parasitoids and hyperparasitoids of the major Lepidopteran pests on 
cabbage in three seasons at the experimental site. Of the species of the three 
important genera of parasitoids recognized worldwide, Cotesia plutellae is the most 
important in southern Ghana. Very little information on parasitoids attacking T. ni 
exists possibly because of its relatively insignificant pest status on cabbage. The 
results of this study have laid a good foundation for further research in Ghana on the 
biology and ecology of parasitoids that would help in our understanding of the 
dynamics in the entire cabbage ecosystem and be exploited for integrated pest 
management strategy to control the pests.
103
CHAPTER FIVE
5.0 DESCRIPTION OF STAGES OF LEPIDOPTERAN PESTS, BEHAVIOUR 
AND DAMAGE
5.1 Introduction
Cabbage is an important vegetable crop worldwide and in Ghana it is the most 
important in the family Cruciferae. However, attack and damage by the complex of 
Lepidopteran pests make its production difficult (Bangnikon, 1996; Obeng-Ofori et 
al., 2007). These pests are however, of unequal importance and their ecological 
characteristics and nature of damage may also differ depending on local climatic 
conditions, country and variety of cabbage (Ooi, 1986; FAO, 1992; Abdel-Razek et 
al.. 2006). There are also variations in biological and morphological parameters of 
the different stages of the pests on cabbage in different locations and countries 
(Salinas. 1986; Sarfraz et al., 2008). It is, therefore, necessary that the specific niches 
that these pests occupy on the plant and the nature of damage caused in relation to the 
cabbage variety, and local conditions should be well understood in order to implement 
effective management strategies. This will also ensure that the parasitoids are 
protected through targeted and more efficient application and appropriate timing of 
insecticides in an Integrated Pest Management programme.
The objective of this study therefore, was to describe the stages of the pests observed 
in this study in relation to behaviour and damage on cabbage to enable their 
recognition, identification and management.
104
5.2 Materials and Methods
5.2.1 Rearing of Lepidopteran Pests
Eggs of P. xylostella. T. ni and S. littoralis attached to cabbage leaves were cut off 
with a pair of scissors from cabbage plants on an unsprayed plot at the experimental 
site in Weija. 39 days after transplanting and taken to the laboratory in the 
Department of Zoology. University of Ghana. Eggs of H. undalis and H. armigera 
were not included as they were not observed. One, three and 10 leaves of cabbage 
were sampled for P. xylostella, T. ni and S. littoralis respectively. Records of the 
distribution and sizes of egg batches on the leaves were taken on the same day. Each 
leaf was cut into six pieces and kept separately on a wet filter paper in a petri dish 
placed on a bench in the laboratory. They were maintained at 12:12 hours of 
light/dark regime till they hatched. Ten newly emerged larvae of each species were 
separated singly into petri dishes on the 3rd day and provided with pieces of young 
cabbage leaves (KJC cross variety) placed on wet tissue paper. The food was changed 
every day till pupation. Daily observations were made on the development, behaviour 
and morphology of the developmental stages of each species till the adults emerged. 
In addition, the patterns of damage by the larvae maintained singly in petri dishes (14 
cm wide) with a whole cabbage leaf and also on cabbage plants in cages in the 
laboratory were observed and photographed.
Forty newly emerged adult males and females of P. xylostella were kept in each of 
two wooden oviposition cages (45 x 45 x 45 cm) with young cabbage plants in water 
and maintained on 10% honey solution soaked in a petri dish. Courtship, mating, and 
ovopisition behaviour were observed at 8 hours, 12 hours, 17 hours and 21 hours for 5 
days. The cages were observed daily and the leaves with eggs were either removed or
105
the whole plant was removed and replaced. Morphological studies were made of the 
larvae, pupae and the adults. All the experiments were carried out at a mean 
temperature of 27 ± 0.2 °C and relative humidity of 55 ± 1.0%.
Visual observations were also made in the field of all the pests (P. xylostella, T. ni, S. 
littoralis. H. undalis and H. armigera) on the seven central plants of the unsprayed 
plots at the experimental site as they were sampled. Observations regarding when 
they appeared on the cabbage plant, their location, posture, feeding pattern and 
movements were recorded and photographs taken.
53 Results
5.3.1 Description of Stages of Lepidopteran Pests, Behaviour and Damage
53.1.1 Plulella xylostella (Linnaeus)
Eggs of P. xylostella were observed on cabbage plants 18 - 19 days after 
transplanting. The female laid her eggs singly or in small batches of two to six, 
usually on the ventral surface of the leaf. For a total of 150 batches of eggs collected 
from the three leaves, 69.3 % were laid on the ventral surface and 30.7% on the dorsal 
surface. Of the 150 egg batches, 48.7% were laid singly, 31.3% in groups of two and 
the rest in groups of three to six (Table 5.1 and Plate 5.1).
Table S.l Percentage of Eggs Laid in a Batch by P. xylostella in the Field
Number of Eges in a Batch % of Total
1 48.7
2 31.3
3 8.7
4 5.3
5 2.0
6 4.0
Number of Batches = 150 
106
in the laboratory, the eggs were usually concentrated at the lowest part of leaves of 
plants standing in water. On two occasions egg batches of 12, 17, and 18 were 
observed very close to the base of the leaf. Sometimes the eggs were deposited very 
close to the leaf stalk. Eggs were also laid on the sides of the cage. The eggs were 
always cemented to the substrate in a way that made it impossible to remove them 
without causing damage to either the eggs or the leaf.
In the field, eggs were often laid close to leaf veins and in depressions on the leaf. The 
eggs were creamy and sausage or oval shaped (Plate 5.1).
Plate 5.1: Eggs of P. xylostella (x 6| on cabbage leaf
The newly emerged caterpillars were pale green, slightly hairy and had black heads. 
As they grew the colour deepened and they lose their hairs. The larvae of P. 
xylostella were more or less spindle-shaped (Plate 5.2). The first instar caterpillars 
buried their heads in the underside of the leaf and fed from there, leaving small 
punctures which made the surface of the leaf looked densely punctured. Even though 
the second to fourth instars also fed from the ventral surface, they chewed from the
107
surface leaving the upper epidermis looking like a pale or white patched area which 
later dried up to form the characteristic ‘windowing’ associated with damage by this 
pest (Plate 5.2). The characteristic black faeces were always associated with damage 
on cabbage.
Plates S.2: Mature larvae of P. xylostella [x 3] and damage on 
cabbage leaf, faeces are arrowed
The caterpillars of P. xylostella started attacking cabbage from two-week old
seedlings to maturity. They were usually found on all parts of the plant but often
concentrated on young leaves in the inner portions of the plant and on the upper
leaves. The young caterpillars sometimes hid in the growing point of the plant and
may go unnoticed. Sometimes, mature caterpillars bored into the developing head or
small mature heads and some effort was usually needed to pull them out. They often
fed close to each other on the leaf and also aggregated on a few plants whilst others
had zero to few individuals on them. The caterpillars were very active and wriggled
violently backwards or dropped off the plant via a silken thread when disturbed. They
hung unto the thread and later climbed back unto the plant. The mature caterpillar
108
could grow up to 12 mm at a mean temperature of 27 ± 0.2 °C and relative humidity 
of 55 ± 1.0%.
Mature caterpillars moved to the lower parts, usually on the ventral surface of the leaf, 
to pupate. They also pupated on the heads when cabbage was maturing. Pupation 
took place after a pne-pupal period of one day. The pre-pupa was either deep green or 
bright green and was enclosed in a woven white silken net-like pupal case (Plate 
5.3a). The pupa turned pale brown after one day (Plate 5.3b) and varied in length 
from 6 to 7.5 mm.
Plate 53a: Pre-pupa of Pla<e 5Jb: Mature Pupa of
P. xylostella |x 6| ? xylostella \x 4)
Adults of the diamondback moth were small slender moths. The male was dark 
brown to dark grey whilst the female was lighter brown. At rest the wings meet 
above the body and display three more or less diamond-shaped pale to creamy 
patterns (Plate 5.4) that extend from the base of the fore-wing along the posterior to 
the pre-apical part. The inner margins of these patterns are slightly darker than the rest 
of the body. At this posture, the rear ends of the wings appear slightly upturned from 
lateral view. The posterior part of the hind wing of the male had a fringe of hairs
109
longer than in the female. As a result, the posterior end of the male appeared wider 
than that of the female.
The typical pale diamond-shaped marks on the wings are less conspicuous in the 
female because of its lighter colour. However, when one is confronted with only one 
sex it may be impossible to sex them using the colour variation.
Plate 5.4: Adult P. xylostella 
(A-Female |x 3.8), B-Male [x 3.51)
The female was smaller than the male and its length ranged from 5 - 6  mm (average =
5.4 mm). Length of the male ranged from 6.5 - 7.5 mm (average = 6.7 mm). Wing 
span was between 12.5 - 14.0 mm and 12-13 mm for males and females respectively.
In the laboratory, mating took place at dusk around 17.30 hours onwards soon after 
adult emergence. Courtship behaviour was exhibited by the male prior to mating. It 
vigorously flapped the wings whilst encircling the female and then attempted to pair 
up with her. Unwilling females were aggressively courted and forcibly copulated 
with. Sometimes, a pair in copula was disturbed by other courting males that 
attempted to dislodge the male in copula. Copulation lasted from 1-1 m hours, during 
which period the pair remained motionless. During mating, the posterior part of the
110
hind wings of the male remained opened and covered the posterior part of the female. 
Pre-oviposition period lasted one day in the populations that were studied.
In the field, the moths hovered about on the lower parts of the cabbage leaf on the 
shady ventral side. On very hot days, especially at noon when temperatures were very 
high between 30 - 31 °C, they sought refuge under the ventral surface of the leaf or on 
the lower parts of the inner surface of the leaves. In such situations, the adults could 
be easily captured. Adults arrive on the cabbage plant at dusk, just before sunset
53.13 Trichoplusia ni (Hubner)
All stages of T ni were found on the underside of the leaf. The eggs were whitish to 
pale greenish and roundish. They were laid singly on the plant. Out o f 100 batches of 
eggs examined on a leaf, 98% were laid singly and one each in batches of two and 
three.
When the eggs were ready to hatch they turned greyish to black. The first larval stage 
of T. ni was pale greenish with black heads and always assumed the typical looping 
posture which made their identification in the field relatively easy. They have three 
pairs of legs on the abdomen towards the posterior region. The young caterpillars 
may have green or black thoracic legs. After the first moult the caterpillars may be 
yellowish green or dark green. The black heads and legs also turned green. They 
turned bright green or became greener as they grew and had two white lateral stripes, 
one on either side of the body (Plate 5.5). Before moulting, the pale lateral stripes 
disappeared and the caterpillar turned very bright green.
I l l
The caterpillar was usually found on the lower leaves of the plant where they were 
almost always in the characteristic looping posture. Occasionally, they might stretch 
out and hold fast tightly with both ends of the body along the leaf especially towards 
the leaf margin. They chewed large pieces of the leaf in between the midribs making 
the leal' skeletonised, or with large open rectangular areas on the leaf. The feeding 
activities of the first and second instars resulted in small roundish holes or punctures 
on the ventral surface. They also moved onto the heart or inner leaves, deep between 
the bases of the cabbage leaves and heads to feed. In this position, the mature 
caterpillars could not be easily noticed on the plant. Their presence may also be 
detected by large accumulations of sticky pale green almost transparent faeces which 
looked like beads at the feeding sites.
Mature T. ni caterpillar usually move down the ventral surface of the leaf to pupate. 
Pupation took place in a loose white silken gauze-like material (Plate 5.6.) usually 
towards the base of the leaf. On older cabbage plants, pupation took place at the inner 
sides of the base of the leaf or on senescing leaves close to the stem of the plant. The 
newly formed pupa is bright green and could be seen lying in its transparent white 
cocoon (Plate 5.6). The pupa turned brown as it aged. It was not tightly glued to the 
leaf and could be easily removed. The pupae ranged in length from 12 to 18 mm.
112
Plate S3: Mature larva of 
T. ni \\  4.8]
Plate 5.6: Freshly pupated T. ni 
[*3.7|
The adult is a brown to dark brown medium sized moth ranging in length from 15-17 
mm. There is a shiny creamish spot and a tear-drop or ‘u’ shaped spot centrally on 
the forewing (Plate 5.7). The two spots may be joined in some specimens. Wing 
span ranged from 27 - 33 mm.
Plate 5.7: Adult of T. ni |x 4.0|
113
53.13 Spodoptera littoralis (Boisduval)
The eggs of S. litloralis were laid in large batches of between 50 and 200 usually on 
the underside towards the tip or middle of the leaf. In a few cases there were less than 
40 eggs per batch. Out of ten batches of eggs collected in the field, two batches 
contained 30 and 40 eggs. The remaining eight (80%) had between 50 and 200 eggs 
per batch.
The eggs were creamy white or off-white and the whole mass was covered with a 
brownish or buff fluffy material (Plate 5.8). The egg mass could be up to three layers, 
with the lowest layer being the largest.
Plate 5.8: Egg mass of 5. littoralis|x 12]
Source: Berg and Cock, 2000
114
At hatching, the caterpillars formed aggregations where they fed and grew rapidly and 
dispersed soon after. In the laboratory, the dispersal commenced after two to three 
days. The caterpillars, at this stage were pale green and had black spots with hairs 
extending out of them. The colour of caterpillars from the same batch of eggs became 
variable as they moulted from one instar to the other but the head remained pale 
brown. The colour of the caterpillars was yellowish pink, pale green, greenish brown 
or pale yellow (Plates 5.9a - d). There was a wider variation in colour in the younger 
instars than in older ones.
Plate 5.9a-d: Variable colouration in young larvae of .V. littoralis
115
At maturity the caterpillar measured between 24 - 27 mm long and the general body 
colour was variable from brown to dark brown. The mature caterpillars were capable 
ot stretching themselves to about one and half times the length to 36 - 50 mm. The 
two black spots behind the head and at the posterior end became more conspicuous 
(Plate 5.10) as they matured. Sometimes the anterior pair was not very conspicuous 
and might be brownish. In addition, there were two pairs of smaller eye-like black 
spots in front of the spots behind the head. These smaller ones had white or pale 
portions near the middle.
Black spot
Source: Berg and Cock, 2000
Plate 5.10: Mature caterpillar of S. littoralis |x 3.51
116
All stages of the larvae of S. litloralis almost always fed on the head of the developing 
cabbage where they were embedded (Plate 5.11). Sometimes force was required to 
remove them out. Younger caterpillars might also be found on the underside of 
leaves up to about 6 days after hatching. Their feeding was associated with dark 
brown wet faeces on cabbage.
Plate 5.11: Larva of S. littoralis |x 2.0| (arrowed) 
feeding on cabbage head
117
In the laboratory, pupation took place after the pre-pupal cuticle had been shed. They 
shortened, and shed the pre-pupal skin one day before pupating. No cell or pupal case 
was formed. The dark brown pupa ranged in length from 15-19  mm, and had a pair 
of spines at the posterior tip (Plate 5.12).
Plate 5.12: Pupa of S. littoralis |x 5| spine arrowed
The adult is a brown to dark brown medium sized moth with white markings. Dark to 
blackish markings were also present on the wings (Plate 5.13). The body length 
ranged from 15-19 mm and wing span ranged from 36 - 41 mm.
Plate 5.13: Adult of S. littoralis |x 2.7|
Source: Berg and Cock 2000
118
53.1.4 Helicoverpa armigera (Hiibner)
Eggs of this species were not encountered in the field during the present study. The 
caterpillar was robust and very intense green in colour and grew up to 39 mm long. 
The head is brownish and there was a white or pale yellow band along the ventro­
lateral side of the body (Plate 5.14a, b). Five pairs of legs were present on the 
abdomen including a pair at the abdominal tip. Segmentation is very pronounced 
(Plate 5.14b). There were three (appearing as one) dark greenish longitudinal stripes 
on the dorsal surface and a pale yellow band on each lateral side of the body. There 
was another pale thin lateral band above the dark greenish band. In each pale yellow 
band, there was a set of spiracles and one small black spot per segment. Each of these 
black spots also had a strand of hair (Plate 5.14b) extending from it  The last 
abdominal segment had a black patch, which slightly expanded towards its posterior 
side. Each of these expanded portions had a tubercle with a strand of hair protruding 
from i t  On the dorsal surface of the caterpillar there were two pairs of tubercles each 
with a hair strand. A pair was located on either side of the mid dorsal dark greenish 
stripe. As the larvae mature, the colour remained green or became variable and 
changed to brown, coffee brown or very dark reddish brown with two black spots near 
the anterior end of the body and the abdominal tip. Colouration of the bands became 
more intense before moulting.
119
Plate 5.14a: Larva of P,ate 514b: Larva of
H. armigera \x 1.5] H- armigera |x 1.7]
Source: Berg and Cock, 2000
Caterpillars of H. armigera always bored deep into the growing point of the cabbage 
during cupping where they fed and subsequently killed it. The feeding typically 
caused rotting or formation of multiple heads. They moved from plant to plant after 
damaging the growing tips. There was no occasion when they were found on any 
other part of cabbage or more than one caterpillar per plant. The presence of this pest 
could be detected by yellowing of buds and the presence of faeces around the growing 
points.
In the laboratory, the mature caterpillar chewed leaf tissue to construct a cell and shed 
off the pre-pupal skin before pupating in the cell. The pupa was brown in colour and 
had a spine at its posterior end.
120
The adult is a robust moth and varied in colour from dull brown or greenish to buff or 
brownish orange. There was a characteristic dark spot towards the anterior margin of 
each forewing and a slightly wavy dark and pale band (Plate 5.15).
Plate 5.15: Adult of H. armigera [x 2]
53.1.5 Hellula undalis Walker <:
Eggs o f this species were not encountered in the field. The caterpillar was small and 
pale pinkish, brownish or dirty green, with characteristic dark reddish or pinkish 
longitudinal thin stripes on the body (Plate 5.16). The two stripes on the dorsal 
surface were more pronounced. There were ten black spots on each segment, with 
three on each lateral side and four on the dorsal surface. It had a small blackish head 
and a black shiny thoracic shield which turned pale as it matured. Mature larvae grew 
up to 14 mm long.
121
Plate 5.16: Larva of H. undalis (x 2.2)
The caterpillar was usually found in the developing bud at the nursery and pre-head 
formation stages. They fed on the bud and typically spun lots of web around 
themselves. This webbing associated with them could be used to detect their 
presence. The webbing and frass completely surrounded the growing point of the 
plant to the extent that it could not grow. When the caterpillars were not in the bud
{
they scraped the epidermis, leaving a thin area on one side. They might also be found 
on the ventral side of the lower margins of leaves near the leaf bases. In this location, 
they rolled the leaf using a whitish silken thread. Only one caterpillar was ever found 
in a leaf roll. Their black faeces lined the rolled leaf and this could also be used to 
detect their presence. Damage by H. undalis to the developing bud usually killed the 
plant or led to multiple head formation.
Prior to pupation, the mature larva spun a thick web for two days and prepared a cell 
from a white transparent silken thread in the tissue paper, which lined the rearing jar.
The shiny light brown pupa was between 7 -10  mm long.
122
The adult is a small, sandy light brown or brown moth with pale wavy transverse 
bands on the wing in the resting position (Plate 5.17). Old specimens lost these bands 
and the insect then generally looked pale. There was a characteristic pair of blackish 
spot or eyes toward antero-apical forewing. The length of the adult was between 7 -8  
mm and it had a wing span of about 17 mm.
Plate S.17: Adult of H. undalis |x 3.6)
53.1.6 Spoladea recurvalis (Fabricius)
Eggs of this species were not encountered on cabbage. The larvae and adults were 
more associated with the weed Cyperus rotundus. When on cabbage, the larvae were 
found in the inner side of young cabbage leaves and wriggled backwards violently 
when disturbed. The caterpillar is small, pale, greenish and transparent. The head 
was brownish and there was a thoracic shield. It had four pairs of abdominal legs 
with an additional two pairs at the abdominal tip. The mature caterpillar grew up to 
15 mm long. Before pupation, it turned bright pink. The pupa was small and pale
123
brown and measured 9 - 1 0  mm long. In the laboratory, pupation took place in a 
white transparent cell.
The adult is a small, dark brown moth of about 13 mm long with a wing span of about 
19 mm. The forewing had a pale or white, vertical band around the mid portion and a 
smaller one near the apex, but not reaching posterior margin (Plate 5.18). There were 
also pale longitudinal bands on the dorsal side of the abdomen. The ventral side was 
pale, with no bands.
Plate 5.18: Adults of S. recurvalis [x 2.0)
S.4 Discussion
This study has provided detailed descriptions of the stages, nature of damage and the 
specific niches of the Lepidopteran pest complex of cabbage under field situations in 
Ghana. All parts of the cabbage plant were utilized by one or more of these pests. 
Most of the existing literature (Talekar and Griggs, 1986; Talekar, 1992; Youdeowei, 
2002; Obeng-Ofori et al., 2007) gave brief descriptions without illustrations on the 
nature of the damage, behaviour or recognition in the field. The diamondback moth.
124
P. xylostella was the ubiquitous pest occurring from the nursery through to crop 
maturity and occurred on all parts of the cabbage plant.
The habit of P. xylostella females laying their eggs in depressions or close to leaf 
veins on the ventral surface rather than on the dorsal surface may have some 
ecological significance. The micro-climate in these habitats may be more favourable 
for development and may also protect the eggs from being easily washed away by 
rain. In the laboratory, the observed preference for laying eggs on the lower part of 
leaves could support the above suggestion. This may also be a specific niche 
requirement since this species occurs together with T. ni, the eggs of which, apart 
from being different in shape, were also laid on the ventral surface. Use could also be 
made of this specific niche characteristic in field identification of eggs of the two 
species.
The results of the present study indicate that the first instar larvae of the diamondback 
moth simply buried their heads whilst feeding and were not leaf miners as reported 
from previous studies (Talekar, 1992). Hardy (1938) observed that when the 
diamondback was provided with very tender leaves, they did not exhibit this 
characteristic.
Dobson et al. (2002) noted that the female P. xylostella moth lacked the characteristic 
pale diamond shape on the dorsal surface of the wing. However, observations on the 
Ghanaian specimens showed otherwise. The lighter colour of the females make the 
diamond shaped patterns less conspicuous.
125
The observation that Hellula undalis feeds on the developing bud of cabbage in the 
nursery as well as in the field supports the recommendation by (Obeng-Ofori et al., 
2007) that control of the pest should start early in the season. In addition, the 
webbing associated with the pest as it feeds obstructs normal growth of cabbage. 
Spodoptera littoralis and H. armigera were considered occasional pests by Brown 
(1975); Talekar (1992); Waterhouse (1992), Berg and Cock (2000). In the case of S. 
littoralis, because of the very large numbers of eggs laid by a single female and the 
dispersal behaviour of the young caterpillars after the first moult on the plant, and the 
fact that they fed on the growing point, could make them damaging to cabbage when 
they occur on i t  On the other hand, H. armigera has been classified by Rowell et al. 
(1992) and Poelking (1992) as minor or a seasonal pest. However, they can be 
damaging even in low numbers considering their behaviour of moving from one plant 
to the other after destruction of the growing tip of the cabbage which led to rotting.
The descriptions and illustrations provided in this study will undoubtedly aid in field 
recognition and identification of the pests and a better understanding of their 
behaviour. It would also allow an informed decision to be made on the spray 
equipment and targeted application of insecticides in an Integrated Management 
Programme on cabbage. The results would also complement the observations by 
Youdeowei (2002) and Obeng-Ofori et al. (2007) as a comprehensive contribution to 
research on sustainable production of cabbage in Ghana.
126
CHAPTER SIX
6.0 DESCRIPTION OF PARASITOIDS OF THE LEPIDOPTERAN PESTS OF 
CABBAGE
6.1 Introduction
The most important parasitoids used in biological control and integrated pest 
management methods against insect pests occur in the order Hymenoptera (CAB 
International 1994; Pratissoli et al., 2008). Fundamental in the development of an 
integrated pest management programme is the correct identification of the insect pest 
involved and its principal parasitoids (Kumar, 1984; Dobson et al., 2002). Of the 
components of integrated pest management, it is biological control which emerges as 
the least understood because of the difficulty of understanding the taxonomy of 
parasitoids (Waage and Greathead, 1992; Bio-NET International Business Plan, 2007- 
2010). Despite the importance of the parasitoids, their taxonomy in most regions 
remain poorly known and their identification is difficult or impossible (Goulet and 
Huber 1993; Bio-NET International, 1999; La Salle, pers comm.). The minute size of 
most of them especially the Chalcidoidea, makes their study unattractive (Boucek. 
1988). Since there can be no meaningful basic or applied entomological research 
until the identity of the organisms involved have been determined (Waage and 
Greathead, 1986; Jones, 1994; Consortium for the Barcode of Life, 2009). taxonomic 
knowledge is greatly needed, especially with projects on control of pests, host 
parasitoid relations, and environmental or faunal studies (Ritchie, 1985; Bio-NET 
International, 2006; Smith et al., 2008).
127
Most of the available keys to parasitoid species have been provided for Europe, North 
America and the Oriental Region (Ferriere, 1929; Burks, 1960, 1965; Riek, 1967; 
Joseph et al., 1973; Boucek, 1988; Narendran, 1989). Unfortunately, in Africa, there 
are either no keys or descriptions and the available keys are out of date and cannot be 
used, thus making identification and recognition of species from this region difficult 
or impossible (LaSalle, CAB1 Bioscience Pers. Comm.)- The situation is particularly 
serious due to lack of references on African entomo-fauna in general, and particularly 
on the parasitic Hymenoptera which contains most of the parasitoids (Risbec, 1951; 
Risbec, 1960; Boussienguet and Neuenschwander, 1989; Gupta, 1991). Other 
problems are the lack of access to type materials and inadequate descriptions without 
illustrations (Boucek, 1988). This Taxonomic Impediment is particularly acute in the 
developing countries (Bio-Net-INTERNATIONAL 2006; Smith et al., 2008).
Taxonomic characterization of local populations of parasitoids is of crucial 
significance in biological control and need to be explored thoroughly if maximum 
benefits are to be expected (Salinas, 1986; Ooi, 1992). In some cases the overreliance 
on identification and taxonomic decisions made by museum workers and the fact that 
specific strains of parasitoids may be associated with specific strains of pests native to 
different countries, have probably restricted biological control research (Fitton and 
Walker, 1992; Sarfraz et al., 2005). Thus, for effective exploitation and utilization of 
the parasitoids associated with the major lepidopterous pests of cabbage in Ghana it 
is crucial that their identities and, especially, their characteristics are documented and 
understood.
128
The objective of this study therefore, was to describe and provide illustrations of the 
parasitoids observed and identified from the Lepidopteran pests on cabbage in 
southern Ghana.
62  Materials and Methods
6.2.1 Identity and Description of Parasitoids
The parasitoids and hyperparasitoids were described based on specimens collected 
and observed from the pests at the experimental site and parts of Ghana For the 
dominant parasitoid species C. plutellae, 25 individuals of each sex were studied 
whilst for the gregarious ones such as Euplectrus laphygmae, Oomyzus sokolowskii, 
Pediobius sp. Tetrastichus atriclavus, Aphanogmus reticulatus, and Elasmus sp., the 
progeny from several hosts were pooled together. The number studied for each 
species therefore varied depending on availability.
The terminologies and classification adopted by (O’toole, 1986; Boucek, 1988; 
Goulet and Huber, 1993) were followed. The antennae and fore wings yield useful 
characters which are important in identification (Boucek 1988; Goulet and Huber, 
1993). Particular attention was therefore paid to these. Where possible, comparisons 
were made with known and related species.
Illustrations were made using a Nikon microscope attached to a Camera 
Lucida/drawing tube, Scanning Electron Microscope, Photomicroscopy, and a Digital 
Camera. Measurements were done on a Nikon microscope fitted with 10 mm. 
micrometer in the eye piece and later converted. Diagrams to explain the 
terminologies used are illustrated in Plates 6.1a and 6.1b.
129
Plate 6.1a Wing illustration Plate 6.1b Antenna illustration
of terminologies of terminologies
m = Marginal vein flag = Flagellum
pm = Post marginal vein fun = Funicle
sm - Submarginal vein an = Anellus
un = Uncus cl = Club
St = Stigmal vein ped = Pedicel
stg = Stigma sc = Scape
6.2.2 Scanning Electron Microscopy
Scanning electron microscopy of specimens of C. plutellae was done at the
Entomology and Nematology Department Gainesville, University of Florida USA.
Specimens preserved in 70% alcohol were removed and dried in a dessicator for four
days. A special sticker was placed on each stub and the specimen was carefully
placed on it to allow rotation at all angles. Each stub had only one specimen placed
on it. The specimens were then placed in a vacuum window of the Sputter Coater
(Denton Desk 2 model) for five minutes to ensure that they were thoroughly dried.
After this, they were coated with gold for three minutes. The stubs were then turned
onto their sides with a pair of curved forceps and coated with gold for three minutes
and a further two minutes making a total of eight. The duration of coating, however.
130
depended on the size of the specimen to be scanned. They were then transferred into 
a specimen holder and placed in a dessicator till they were ready for scanning electron 
microscopy.
A Polaroid Positive - Negative 4 x 5  Instant Sheet Film was used. After processing 
the photographs, the negatives were separated from the print and immediately cleared 
in Sodium sulphite solution for about four minutes and then drained for a few 
seconds. They were then washed in running water for about five minutes after which 
they were hunged to dry for later printing using conventional techniques. The prints 
were immediately coated after processing to protect them against scratching and 
fading. The coating was applied to the prints including the borders, in six to eight 
overlapping strokes to ensure entire coverage. They were kept separately from each 
other on a flat surface until they were thoroughly dry.
6.23 Photomicroscopy
Different methods were used for dry specimens and wet specimens i.e. those that 
could not be taken dry because the cuticle collapsed when out of the preservative.
The photographs of the wet specimens (preserved in 70% alcohol) were taken on an 
Olympus OM2 Macro Photography System using extension bellows. The system was 
fitted with a macro 38 mm lens and set at F 22 or F16 with Olympus T10 flash ring. 
This system allowed the photographs to be taken through liquid. An ordinary daylight 
film was used. The specimens to be photographed were taken out of alcohol and 
thoroughly cleaned after which they were placed in alcohol in a glass stage prepared 
from a petri dish and a rectangular piece of clear glass. The alcohol level in the stage
131
was such that no meniscus occurred between the specimen and the alcohol level since 
that would interfere with the reflection of the specimen. It was also necessary not to 
use too much alcohol as this would cause the specimen to float. Photographs of the 
dry specimens were taken with a microscope fitted with an Olympus camera.
63 Results
63.1 Identity of the Parasitoids
Thirteen species of Hymenoptera and two species of Diptera were identified as 
parasitoids and/or hyperparasitiods of the pests on cabbage (Table 6.1). Seven were 
identified to species, two to species groups and the rest to generic level.
Table 6.1 Identity of the Parasitoids / Hyperparasitoids Recorded from the
Lepidopteran Pests on Cabbage
Superfamily Family / Subfamily Species
Cbalcidoidea
Ichneumonoidea
Cerapbroooidea
Muscoidca
Braconidae / Microgastrinae 
Braconidae / Cheloninae 
Ichneumonidae 
Chalcididae / Brachymerinae 
Chalcididae / Haltichellinae 
Elasmidae
Eulophidae / Eulophinae 
Eulophidae / Tetrastich inae 
Eulophidae / Tetrastich inae 
Eulophidae / Entedoninae 
Eulophidae / Eulophinae 
Pteromalidae / Pteromalinae 
Ceraphronidae 
Tachinidae 
Tachinidae
Cotesia plutellae 
Chelonus curvimaculalw 
Charops sp.
Brachymeria sp.
Hockeria sp.
Elasmus sp.
Euplectrus laphygmae 
Oomvzus sokolowskii 
Tetrastichus alriclavus s. i 
Pediobius sp. 
Nolanisomorphella sp ** 
Trichomalopsis sp. 
Aphanogmus reticulatus 
Blepharella curvimaculatus 
Perihaea orbata
** flaviventris group.
132
63.2 Descriptions of the Parasitoids
63.2.1 Ichneumonoidea
Cotesia plutellae (Kurdjumov) = Apanteles plutellae Kurdjumov (Braconidac)
Both sexes of C. plutellae are similar in general appearance. They are black but the 
female has slightly pale brown lateral areas (not very sclerotised) on the antero-dorsal 
abdomen (Plate.6.2). The lateral areas vary in intensity of the colouration or 
sclerotisation. The gaster is shorter than the mesosoma. The anterior three quarters of 
the sternum of the female gaster is brownish (lightly sclerotised) with the remaining 
posterior part black. This lightly sclerotised part often collapses when the specimen 
dries up. Venation of the forewing is well developed, but the apical veins are 
nebulous (faint). A strong pigmented spot is present about two-thirds towards the 
anterior margin of the fore wing (Plate 6.2 arrowed).
In the males the dorsal part of the entire abdomen is usually black. Only a small 
portion of the anterior part of abdominal sternum is lightly sclerotised. As a result the 
females appear generally lighter coloured. Apart from the ovipositor, this can be used 
to easily separate the males from females. The legs are hairy and uniformly brownish 
except the hind femur and tibiae which have dark apices. A trochantellus is present
Plate 6.2: Female Cotesia plutellae |x 13)
133
between the coxa and the trochanter. The mid and hind tibiae have two apical spines, 
the inner one being the shorter of the two. There are five tarsal segments. Tarsal 
segments of the hind-legs are darker than those of the fore-legs and the mid-legs. 
First tarsal segment is the longest of the tarsal segments. Vein 2-M of fore-wing is 
nebulous. Vein lr-m of hind-wing is more or less basal of SC+R (Plate 6.3).
Plate 6.3: Schematic diagram of fore-wing and 
hind-wing of C. plutellae [x 17|
Key
2M = Second Median Vein
SC+R = Sub-Costal and Radial Vein
Ir-m = Vein joining the Radial and Median vein
134
Significant differences exist between male and female with regard to body 
measurements of C. plutellae. The average length of female is 2.49 ± 0.02 mm and 
that of the male is 2.16 ± 0.02 mm. Abdominal width is 0.46 ± 0.03 and 0.49 ± 0.03 
mm for males and females respectively. The antenna is made up of 17 segments plus 
a radicle (Plates 6.4a, b). The scape is bulbous but the rest of the segments are 
elongated and similar in length.
Plate 6.4 a: Schematic diagram of Plate 6.4 b: Schematic diagram of
antenna of male C. plutellae (x 20| antenna of female C. plutellae |x 20|
135
The Scanning Electron Micrographs showed that sexual dimorphism exists in the 
length and hairiness of segments of the antennae (Plates 6.5a, b). The male segments 
have longer and denser hairs than in the females. In addition, the apex of the last 
segment is blunt in males whereas it is pointed in the females. In both sexes there is a 
pair of conspicuous stiff hairs at the apices.
Plate 6.5a: Scanning electron 
micrograph of female 
antenna |x 240)
Plate 6.5b: Scanning electron 
micrograph of male 
antenna [x 300)
136
The frons. including the genae, are very hairy with the former being wider than long. 
The vertex is especially very hairy (Plate 6.6). The clypeus is broad and the margin 
curves inward at the middle. Malar sulcus is present at the malar area. An anterior 
tentorial pit is conspicuously present on either side of the clypeus. The antennae 
articulate with the head high above the clypeus.
o
Plate 6.6: Scanning electron micrograph of 
facial view of C. plutellae |x 110)
The mesosoma has various punctures and striae on the dorsal surface. The pronotum 
is not well developed but the prostemum is made up of two large sculptured plates 
(Plate 6.6). The mesoscutum has a higher concentration of hairs than on the other 
nota (Plates 6.7a, b). Well developed tegulae are present. The scutellum has a 
distinct slightly raised triangular mid portion surrounded by well developed striae. A
137
deep sulcus is present on either side of the scutellum. The posterior margin of the 
scutellum is deeply convex. The metanotum has two rounded sulci at the mid anterior 
margin (Plate 6.7a). On either side of each sulcus a row of striae is present. The 
pleural side of the thorax (mesosoma) is much smoother. The mesopleuron has three 
plates/sclerites, a smaller anterior triangular piece and a bigger posterior more or less 
rectangular piece. A much smaller piece joins these two. The triangular piece has a 
row of striae about one third way up from the longer side (Plate 6.7b). On the larger 
sclerite a row of deep punctures occur along the upper and right lateral margins. 
Another faint row of punctures extends from the left side but becomes faint as it joins 
the right lateral margins. The propodaeum is heavily punctured.
Plate 6.7a: Scanning electron Plate 6.7b: Scanning electron
micrograph dorsal view of micrograph lateral view of
mesosoma |x 90) mesosoma |x 66)
138
Chelonus curvimaculatus Cameron (Braconidae)
It is a medium size parasitoid measuring 5.5 mm long. The body has a dense mat of 
short pale hairs and a long (at least 27 segments) black antenna of about 3.5 mm in 
length. The head and thorax are black and highly punctate. It has three Ocelli, with 
dark brownish eyes. The antennae arise high above the clypeus on the vertex (Plate 
6.8b) and almost between posterior ends of eyes. The fore leg is very short, and the 
coxa and trochanter are black. The basal part of the femur and the last tarsomeres are 
dark, but the rest of the fore-leg is pale brown. A curved tibial spur is present The 
mid-leg is long and has a black rounded coxa covered with a dense mat of hairs. The 
trochanter is about as long as the coxa. The basal half of the mid-femur is slightly 
dark and the apical half is pale brown. The tibia has two apical spurs which are not 
curved. The hind-leg is the longest, and the femur is well developed and appears 
swollen. The hind coxa is not as rounded as it is in the mid coxa. The coxae, 
trochanter and femur are black. The apical half of the tibia is very dark. There are 
two apical tibiae spines of unequal lengths.
Metasomal terga 1-3 are fused and form a carapace (Plates 6.8a, b) which covers the 
remaining terga. The tip of the carapace is rounded and curves ventrally, as a result of 
which the apex of the abdomen is concealed. The carapace is black and has a pale 
anterior dorso-lateral bands which do not touch each other in the middle of the 
dorsum. The anterior-most part of the carapace is black but the lateral margins are 
slightly pale. There is an equivalent pale creamy band on the sternum of the 
metasoma. The first tarsomere is the longest in all the three legs.
139
Plate 6.8 a: Adult Chelonus curvimaculatus |x 4.0]
Plate 6.8 b: Schematic diagram of 
C. curvimaculatus |x 15| to show carapace
Source: Goulet and Huber, 1993
140
Charops sp. Ichneumonidae
This is an elongated dark parasitoid. Length of male is 9.67 ±0.13 mm. Female is 
13.16 ± 0.31 mm long including the ovipositor. The thorax and propodaeum 
(mesosoma) are highly sclerotised and punctuate (Plate 6.9). Head is Ienticulate 
(antero-posteriorly depressed) with very long antennae almost as long as the fore wing 
(Plate 6.9). Fore and mid legs creamish or pale except tarsi which are dark. Hind legs 
are dark and two tibial spines are present at apices.
Punctate
mesosoma
Plate 6.9: Female Charops sp. |x 7.0]
141
Venation is well developed and complete, fore wing with vein 2m-cu tubular in part 
(Plate 6.10). Hind-wing with vein lr-m distally of distal end of vein SC+R.
Plate 6.10: Fore and hind wings Charops sp. [x 16]
63.2.2 Chalcidoidea
Brachymeria sp. (Chalcididae)
This is a black medium sized parasitoid measuring 5.5 mm long. The entire body is 
heavily sclerotised; head and mesosoma especially heavily punctate. Mesosoma is 
convex and coarsely punctured and with numerous conspicuous short hairs. The 
antenna is short. Tegulae and tibiae are yellowish. The proximal part of the femur is 
black, with the remaining parts of the leg pale.
The hind femur is greatly enlarged, compressed and almost oval shaped (Plate 6.11). 
It is about 2 times as long as wide and ventrally dentate with eight teeth. The 
proximal five teeth are more developed and widely spaced, but the remaining ones are 
closely spaced and smaller. There is a row of white hairs along the ventral part of the 
hind femur. The hind tibia is distinctly curved and has a groove into which the femur 
fits or locks at rest. The apices are truncate and slightly pointed at one side. The fore
142
and mid legs are similar in size and colouraion. The propodaeum has some alveoli on 
the anterior part and a median carina. The ovipositor is very thick and extends 
slightly beyond the tip of the abdomen. The first gastral tergite is enlarged, and it is 
almost as long as the rest of the gastral segments together.
Plate 6.11: Female Brachymeria sp. (x 20]
Hockeria sp. (Chalcididae)
This is a medium sized black Chalcid of length 2.2 mm for males and 2.3 - 2.4 mm 
for females. It is ant-like in appearance with relatively long legs and is not active. 
The body is very punctate and highly sclerotised. It has large eyes which are pale. 
The coxae are black, hind femur black and enlarged with spines at the apex. There is 
a long curved grove on the inner side of the tibia into which the femur fits when at 
rest. The hind tarsus is brownish, apex of mid femur thickened or swollen and darker 
than rest of the leg segments which are brownish. The first tergite of the gaster is 
longer than twice the remaining ones put together (Plate 6.12). The posterior tergites 
of the gaster are short and overlap or appear to telescope into each other. The gaster
143
is more or less convex and slopes forward. The ovipositor is stout and extends 
slightly beyond the tip of the gaster.
Antennal
insertion
Plate 6.12: Female Hockeria sp. |x 40]
It exhibits sexual dimorphism in the antennae. The antennae arise very close to the 
clypeus, elbowed and twelve segmented. In both sexes the scape is very long. In the 
male, the scape and pedicel are dark brownish with the remaining ten black. In the 
female, the scape, pedicel and first segment of the flagellum (flagellomere) are 
distinctly light brownish with the remaining black (Plate 6.12). The wings have two 
wide dark vertical bands on them. The stigmal vein is very short, postmarginal vein is 
shorter than marginal vein (Plate 6.13).
144
Plate 6.13: Schematic diagram of 
fore-wing of Hockeria sp. [x 40)
Elasmus sp. Elasmidae 
Female
The female of this species is bigger than the male. It is slim and elongated and 
measures 3 mm in length. It is distinctly brightly coloured orange and black (Plate 
6.14). The head is lenticulate (depressed), yellowish, black setose vertex and frons. 
Malar area groove is not well defined. The eyes are well developed and conspicuous 
and pale with a tinge of mauve or pink, and surrounded by darkened area. The pro- 
notum is black dorsally but the pro-stemum is orange. The Meso - scutum is orange 
with black transverse bands, heavily and conspicuously setose. The posterior margin 
of the meso-notum has a blackish transverse band narrower in the middle but wider 
under the fore wing bases. There are two very conspicuous setae at inner base of 
wing, and another pair at outer base of wing. Tegulae black and well developed. The
145
meta-notum is yellowish and black with two conspicuous setae. It extends backward 
such that the propodaeum is not easily visible; petiole transverse making the joint 
between it and rest of gaster appear broad, somewhat like that of a sawfly 
(Symphyta). The propodaeum is emarginated postero-laterally. This species is 
shaped like a keel or wedge (Plate 6.14). The legs are uniformly pale brown coloured 
with dark margins. The gaster is elongated and pointed at the apex (ovate), dorsal 
surface flattened, posterior segments with dorsum black. The ovipositor is short and 
extends slightly beyond apex of abdomen
Plate 6.14: Adult male (x 17.5] and 
female (x 16] Elasmus sp.
The antennae of the female are brownish orange and hairy and arise very close to the 
clypeus. They are nine segmented. There are seven flagellomeres (Plate 6.15) made 
up of one small anellus, 3 segmented funicle and a three segmented club. The apical 
segment of the club is narrower than other two. The basal segment of the funicle is 
slightly narrower than the other two (Plate 6.15). The pedicel is about 2 V2 times the 
length of the scape. A conspicuous radicle articulates with the torulus.
146
Radicle
3 segmented 
club
Plate 6.1S: Schematic diagram of antenna of 
female Elasmus sp. [x 120]
The hind coxa of this species is very large and compressed like a disc and appears flat 
in lateral view (Plate 6.16). It is accommodated in the emarginate postero-lateral part 
of the propodaeum. The meso-femur and meta-femur are conspicuously compressed 
and elongate oval. The meso-tibia has a sub apical spine. The meta-tibia also has a 
very long sub-apical lobe-like setae and a smaller one. In addition the meta-tibia has 
diamond shaped patterns formed by a dense row of conspicuous flattened, short black 
bristles (Plate 6.16) arranged in a continuous line which loops back on itself to form 
apparently closed cells. In latero-dorsal view, seven of the bristles, of which two are 
bigger than the rest, are clearly visible. In lateral view only four are visible. The 
tarsus has four tarsomeres and in lateral view is uniformly pale, narrow and elongate. 
The first tarsomerc is the longest.
147
Plate 6.16: Schematic diagram of hind leg of Elasmus sp. |x 55)
Venation is greatly reduced. The forewing is densely setose (has numerous short 
hairs) over a pale brown background, and is distinctly elongate and narrow with a 
rounded apex (Plate 6.17). The sub-marginal vein is longer than the post-marginal 
vein. The marginal vein is very long, post-marginal vein short, stigmal vein sessile 
and pale. A dense row of short hairs occurs at the apex of the wing (Plate 6.17). The 
length of the wing is about three and half times the greatest width.
Plate 6.17: Schematic diagram of forewing of female 
Elasmus sp. |x 40]
148
Male
The male is smaller (2mm) and dull coloured with black and brown metasoma (Plate 
6.18). Head and face are black and setose. Mesosoma is black, except meso-stemum 
and distal parts of coxae. Antenna is moderately long, branched (Plate 6.18) and ten 
segmented. The antenna has a broad scape, short pedicel and eight flagellomeres: a 
small ring-like annelus, four segmented funicle and three segmented club. Three long 
lateral hairy extensions (rami) arise from the three basal funicular segments thus 
making it appear like a feather. Apical segment of club of flagellum tapers to a point.
\
\
Plate 6.18: Adult male Elasmus sp. 
to show branched antennae |x 301
Head and Mesosoma are black, metasoma (abdomen) dark and brownish orange. 
Posterior 2/3 of dorsum of metasoma is dark to black, anterior 1/3 brownish with a 
darkened anteriormost part. The anterior 2/3 of meta-sternum is brownish and 
posterior 1/3 is dark. The wings and legs are similar to those of the female, but the
149
legs are slightly darker. The gaster is more rounded than in the female, shorter and 
not keel shaped.
Euplectrus laphygmae Ferriere (Eulophidae)
These are small insects with the length of male ranging from 0.9 -1.2 mm and 1.2 -
1.6 mm for females. The size depended upon the number of individuals emerging 
from a host Males and females are similar and generally black and lack metallic 
luster. The body shrivels or collapses when dried. Head lenticulate and, together 
with the mesosoma, longer than the gaster (metasoma) which is very short in both 
sexes (Plate 6.19). Gaster is about 3 times the length of head plus mesosoma. The 
mesosoma is black and gaster brownish or lighter. Female is bigger and generally 
darker than male. Both the male and female are very bristly with conspicuous long 
bristles on head and mesosoma
Plate 6.19: Male |x 44| and female |x 46) 
E. laphygmae
150
The head of the female is black except the mouth parts area below the antennae 
(lower face) and genae which are yellowish (Plate 6.19). The area surrounding the 
eye is black. The entire head of the male, including the face is pale. The abdomen is 
coloured as in females but slightly paler. The antenna of the male is pale, eyes 
slightly reddish and smaller than in the female.
The antenna is inserted at the level of the eyes. The genae are conspicuously longer 
than the distance between the eye margin and vertex. Seven pairs of conspicuous 
bristles are present on the vertex Mid frons. The first pair at the base on the inner 
proximal part of eyes points inwards, the second pair between the lateral ocelli points 
inwards, the third pair at base of median ocelli point outwards. One pair at the base of 
distal part of eyes point outwards and the remaining three pairs on the frons, including 
a few smaller ones. At least eight pairs of conspicuous brisdes on mesonotum and 
metanotum. The legs are relatively long compared with the body and are paler than 
the body.
The pronotum is short and has fine transverse carina at anterior margin. Mesonotum 
arched with different sculpture in middle and side, roughly reticulate in the middle, 
but more finely on the sides, and lacks carina. The scutellum has no longitudinal 
lines, rather fine sculpture and two pairs of setae. A conspicuous bristle is present at 
the base of the tegulae. The Sub-lateral lobe of the metanotum has a row of eight 
bristles.
151
Sub-marginal vein of forewing with five setae, with no interruption from marginal 
vein, distal end smoothly curved into parastigma. Stigmal vein long but shorter than 
post-marginal vein and ends in an uncus and stigma (Plate 6.20). A conspicuous seta 
on submarginal vein points inwards.
Plate 6.20: Schematic diagram of fore-wing 
of male E. laphygmae |x 301
and hind-wing
152
Hind tibiae with two spurs, one longer than the other. One spur is distinctly longer 
(Plate 6.21) than the basitarsus (basal tarsomere).
Plate 6.21: Schematic diagram of hind­
leg of E. laphygmae |x 90)
The antenna of the female E. laphygmae is hairy, yellowish and seven segmented. A 
radicle is present and the flagellum is 5 segmented. Short inconspicuous anelli occur 
between all the antennal segments except between the basal flagellomere and the 
second and also between the fourth flagellomere and the club (Plate 6.22). The anelli 
are so inconspicuous they can be easily overlooked. The Scape is long and the 
pedicel is the narrowest segment. Club is apparently two segmented (slight 
depression laterally) and pointed at apex. Gaster with dark lateral sides, rest brownish 
yellow, ovipositor very short and inconspicuous.
153
Plate 6.22: Schematic diagram of antenna of 
female E. laphygmae (x 100)
The antenna of the male E. laphygmae is also seven segmented with a conspicuous 
radicle (Plate 6.23). The flagellomeres except the basal one are shorter and more 
rounded than in the females. The Club has a very slight lateral depression.
154
Plate 6.23: Schematic diagram of antenna of 
male E. laphygmae (x 100)
Notanisomorphella sp. (Eulophidae)
This description is based on male specimens. This species appears generally black. 
The head and mesosoma are darker than the metasoma. The branched antennae are 
inserted quite close to the clypeus (Plate 6.24). The mesonotum with notauli 
incomplete. Scutellum without sub-lateral grooves, bare except for four setae. Wings 
long and wide, about two times as wide as long at the greatest width. Stigmal vein 
moderately long with conspicuous parastigma, post marginal vein distinct and longer 
than stigmal vein. Legs are similar in development. Proleg and midleg pale but hind
155
ones dark. Tibia straight, hind coxa with fine sculpture. Hind tibiae with posterior 
two-thirds of femur black, apices slightly pale, basal one-third pale, posterior half of 
tibiae dark. Petiole short, transverse, and not conspicuous (Plate 6.24). Gaster 
dorsally not highly sclerotised and collapsible especially lateral sides. Propodaeum 
with large reticulate median area and strong median carina (Plate 6.25).
This species was identified using the key by Boucek (1988) and confirmed by La 
Salle (CAB Bioscience British Museum Natural History, London). Boucek (1988) 
recognised two species groups (proserpinensis and jlaviventris) based on the nature of 
the propodaeum. The specimen described here falls in the Jlaviventris group 
(propodaeum punctured-reticulate).
Short trans' 
petiole
Collapsible
gaster r
Plate 6.24: Male 
Notanisomorphella sp. |x 211
Plate 6.25: Propodaeum and 
carina |x 2*)]
Source: Boucek, 1988
156
Antennae nine segmented and branched (Plate 6.24). The flagellum is seven 
segmented, brown and sparsely setose. Pedicel more or less rounded and shorter than 
basal flagellomere (Plate 6.26). Third flagellomere shortest of the flageilomeres. 
Pedicel plus four basal flageilomeres longer than fifth flagellomere. Fifth 
flagellomere almost as long as the two apical segments. Three long rami (branches) 
arise from the first two basal flageilomeres and fourth flagellomere (Plate 6.26). 
Rami appear to be somewhat jointed and bear conspicuous long setae which point 
upwards. First ramus arises from base of first flagellomere. The second arise sub- 
basaliy from second flagellomere, the third sub-basally from the fourth flagellomere
Plate 6.26: Schematic diagram of male antenna 
/Votun isomorph ell a sp. |x 90|
157
Oomyzus sokolowskii Kurdjumov (Eulophidae)
This is a tiny ant-like (about 1mm long) metallic green species with a tinge of black. 
It is similar in appearance to Tetrastichus atriclavus s. 1. recorded in this study. It is 
short with a convex mesosoma (Plate 6.27). Legs pale, middle portion of femur and 
coxae black. Fore and mid tibiae yellowish, hind tibiae pale. The tarsal segments are 
dark but not as black as coxa. Sub-median grooves on scutellum well developed and 
are close to each other. Male antenna is more hairy than in female.
In females the antenna is stout, nine- segmented and brownish. A small annelus is 
present between the pedicel and the first flagellomere (Plate 6.28). Flagellomeres are 
almost quadrate. There is a three-segmented compact club which is shorter than the 
three funicle segments together. In males, the antenna is eleven segmented, longer 
than that of the female, and bears whorls of very conspicuous setae (Plate. 6.29). 
Segments beyond the pedicel have longer hairs on the lateral sides. Scape about three
Femaie \1 le
Hairy antenna
Plate 6.27: Female [x 50| and male |x 53|
O. sokolowskii
158
times the length of pedicel. A small annelus is present between the pedicel and first 
flagellomere and between the latter and the second flagellomere. Club elongated and 
not compact and has a pointed tip. Club shorter than all funicle segments put 
together.
Plate 6.28: Schematic diagram of Plate 6.29: Schematic diagram of 
antenna of female |x 82] O. antenna of male |x 65| O.
sokolowskii sokolowskii
159
Fore-wing with stigmal vein longer than postmarginal vein (Fig. 6.30). One bristle on 
submarginaJ vein. Forewing with a row of hairs along posterior half margin.
Stigmal
vein
Row of 
hairs
Submarginal vein 
with one bristle
Postmarginal
vein
Plate 6.30: Schematic diagram of fore-wing 
of O. sokolowskii (x 40]
160
Tetrastich us atriclavus s. 1. (Waterston) (Eulophidae)
This species has a slight metallic bluish black sheen and has a narrower and longer 
abdomen (Plate 6.31) than Oomyzus sokolowskii described above in (Plate 6.27).
Plate 631: Female Tetrastichus atriclavus s.l. |x 68)
Striae present on face, scutellum with two notauli (longitudinal grooves) and an 
admarginal grooove. Notauli is entire and linear. Forewing venation interrupted at 
base of parastigma. One bristle present on submarginal vein, post marginal vein 
absent Propodaeum reticulate with an inverted ‘Y’ shaped carina. In females eyes 
are red and head looks rather stout and more or less rounded. Club and funicle darker 
than scape and pedicel. Females with three pairs of well developed setae on left side 
and two pairs on the right side of notauli. This species has a large black coxa and a 
femur which is black from the bases. Remaining parts of legs pale except tarsi with 
darkened apices. Scutellum with two grooves and setae on dorsal surface. Gaster of
161
female longer than head and mesosoma together. Thin ovipositor protrudes slightly 
beyond the abdomen.
Antenna is nine segmented with a three segmented compact club which appears like a 
single segment. There is a small ring-like annelus between pedicel and first 
flagellomere (Plate 6.32). In males antenna is black and also nine segmented.
Ring-like Compact
Anellus Club
Plate 6.32: Schematic diagram of antenna of female 
Tetrastichus atriclavus s.l (x 80)
This species was identified as T atriclavus Waterston based on the presence of one 
dorsal bristle on the submarginal vein (Polaszek and La Salle 1995). The similar 
species T. howardii (Olliff) has two setae on the dorsal surface of the submaginal 
vein. T. howardii is mainly an Asiatic species but has been imported into Africa for 
investigation in biocontrol programmes (Kfir, 1991; Kfir et al., 1993). It had. 
however, not been rccordcd in Ghana.
162
Pediobius sp. (Eulophidae)
Both male and female of this parasitoid are small and similar in appearance. Body 
length is 1 - 2 mm long. They are metallic dark with a tinge of bluish green, 
especially on the mesosoma and metasoma (Plate 6.33). The entire body is strongly 
sclerotised and bristly. Female longer than male, length about two times that of male, 
elongate/ovate gaster with seven exposed segments, ovipositor short and stout In 
male mesosoma is longer than metasoma, metasoma rounded, short and truncate 
(Plate 6.33).
A
Head and
  prothorax
of male
_____ Bristles 
metasoma
f em a le  M a l e
Plate 6.33: Female |x 29| and male |x 321 Pediobius sp.
The metasoma in males has pale bristles at apex, rest with sparse hairs. Only four
segments visible on gaster, first tergite longer than the rest. Mesosoma and metasoma
is more shiny in the male with a bluish green, terminal segments darker. Prominent
petiole present, expanded at anterior and wider than long. The face and genae of both
male and female are bright shiny green with a tinge of blue. Frontovertex more or
less rounded dorsally, reticulate dark and shiny with a tinge of bluish green. Genae in
163
facial view is straight and moderately long. Antennae inserted at about level of eye. 
Antenna of male is hairy, brownish and slightly longer than in female. Eyes are 
divergent (widely separated). Brownish bristles on vertex around oceliar area. Head 
wider than long. Mesosoma and metasoma of both male and female are strongly 
reticulate and with pale prominent setae, scutellum finely reticulate with setae on 
subscutellum. Pronotum short with collar bearing a strong raised posterior margin 
like a carina. Anterior of pronotum of male dark reddish brown. A pair of spines on 
either side of pronotum. Femora and tibiae darker than antennae. Hind leg more 
developed than rest with tibial apical spine straight and dark. Coxae are large. From 
coxa up to tibia are dark reddish brown with a tinge of bluish green. Tarsomeres 
whitish except the last tarsomere; base of first tarsomere darkened. Forewings 
hyaline with pale brown background. Submarginal vein with two dorsal bristles; 
marginal vein prominent with a row of brownish spines, stigmal vein short with uncus 
and stigma. Postmarginal vein very short and faint and shorter than stigmal vein.
The antenna of females is six segmented, but club slightly divided into two on lateral 
sides. Scape bulges at the middle portion, longer than two times the length of pedicel. 
Pedicel is narrow at base. Three funicular segments with small anelli in between 
(Plate 6.34). First funicle segment longer than the 2nd and 3rd segments. Scape longer 
than club. Club with a conspicuous spine at apex. Second and third funicle segments 
and club with long hairs on sides, four on one side and three on the other side (Plate 
6.34). First funicle segment and pedicel with hairs mainly on one lateral side.
The antenna in males is six segmented, the apical segment apparently divided into 
two, with the distal part ending in a spine-like process (Plate 6.35). The shortest
164
segment is the pedicel that is somewhat rounded but slightly narrower at base. A 
small anellus is present between scape and pedicel. The three basal flageilomeres are 
cylindrical but slightly bulges along the sides and are similar in size (Plate 6.35). The 
apical club plus the spine is about as long as the scape. In-between the flageilomeres 
there are inconspicuous ring-like anelli.
Plate 6.34: Schcmatic diagram of 
antenna of female Pediobius sp. |x 112]
Plate 6.35: Schematic diagram of 
antenna of male Pediobius sp. |x 98]
165
Trichomalopsis sp. (Pteromalidae)
The females and males are similar in appearance (Plates 6.36 and 6.37). They are 
blackish with a tinge of bluish-green, ant-like, and not very active. The length of the 
females range from 2.0 - 2.3 mm, and the males range from 1.7 - 2.0 mm. The 
antennal is insertion high above clypeus. Distance between point of antennal 
insertion and vertex is shorter than length of scape. Both sexes have geniculate 
antennae. The antennae of the female are dark brown except at the tip of the club 
which is slightly pale (Plate 6.36). Eyes are large and black. Head longer than wide 
from vertex. Occipital carina strong in postero-dorsal view. Mesosoma almost as 
long as metasoma and bulges on dorsal surface with a distinct pronotal carina. The 
legs are brownish but in males the coxae are blackish. The foreleg has a well 
developed sub apical spur which curves slightly towards apex. Midleg with straight 
sub-apical spur. Metasoma with clear segmentation. Ovipositor as thick as tibiae and 
protrudes slightly beyond metasoma. Wings are transparent with a light smoky 
appearance (Plates 6.36 and 6.37).
Plate 6.36: Female |x 25| Plate 6.37: Male |x 22|
Trichomalopsis «tp. Trichomalopsis sp.
The antenna of the female is eleven segmented with a long scape (about two thirds the 
length of the rest of the antenna (Plate 6.38). The base of the pedicel is constricted. 
Two small anneli are present between the pedicel and first fiagellomere. An anellus is 
present between flagellomeres 3, 4, 5, 6 and the basal segment of the club. 
Flagellomeres 3 - 6 are somewhat quadrate, 5 and 6 wider than long. Well developed 
stout club which is 3 segmented. The apical segment of the club is smaller than the 
other two.
Long Scape
Plate 6.38 Schematic diagram of antenna of 
female Trichomalopsis sp, |x 67]
The antenna of the male is also eleven segmented but more slender than in the 
females (Plates 6.38 and 6.39). A radicle is present. There are two small anelli 
between the pedicel and the first fiagellomere and also between third to the basal club 
segment. The first fiagellomere bulges laterally, second to fifth longer than wide, 
sixth wider than long (Plate 6.39). The club is more elongated than in the female and 
not as distinctly segmented, middle segment longest.
167
Plate 6 .39: Schematic diagram of antenna of male 
Trichomalopsis sp. [x 72]
The fore-wing is lightly setose. The submarginal vein is about twice as long as the 
marginal vein. The stigmal vein is well developed with a distinct stigma but shorter 
than post-marginal vein (Plate 6.40).
168
Plate 6.40: Schematic diagram of fore-wing of 
Trichomalopsis sp. |x 82]
63.2.3 Ceraphronoidea
Aphanogmus reticulatus (Fouts) (Ceraphronidae)
This is a small dark brown to black parasitoid. The antennae arise below the eyes and 
immediately above the clypeus in both sexes. There is sexual dimorphism in the 
antennae and in body size (Plate 6.41). The male antenna is slender and more hairy 
than that of the female (Plates 6.41 and 6.42). The female is bigger and more robust 
than the male and its length range from 1.1-1.3 mm. Body length of male range from
0.9-1.2 mm. Legs of both sexes are light brownish. The wings are shiny and 
iridescent. Forewing with a narrow linear stigma. Mesosoma is quadrate in both 
sexes. Meso-tibia has one spur.
Female: Eyes are large and brownish. The antenna is geniculate and slightly curved 
towards the distal part. The Scape, pedicel and first flagellomere (first segment of 
flagellum) are brown; remaining segments brown to black (Plate 6.41). The apex of
169
the last antennal segment is paler. Mesosoma is darker than metasoma and both are 
stout. The metasoma is wide at the base and parts of the posterior end are brownish.
Male: Eyes are blackish or dark brown. The antenna is uniformly brown apart from 
the scape which is slightly pale.
Quadrate
mesosoma
Quadrate
mesosoma
Antennal
insertion
Male Female
Plate 6.41: Male |x 25| and female |x 41) 
Aphanogmus reticulatus
Plate 6.42: Male |x 40| A. reticulatus
170
The antenna of the male is moniliform and has eleven segments (Plate 6.43). Apart 
from the scape, the segments are generally similar in shape and have rounded apices. 
The club has a slightly constricted base. It is longer than the flagellomeres but shorter 
than the scape.
Plate 6.43: Schematic diagram of antenna 
of male A. reticulatus |x 96|
The antenna of the female is ten segmented (Fig. 6.44) and has short hairs on all 
segments. The scape is the longest segment with a constriction towards the base, 
giving it the appearance of a flask (Fig. 6.44). A small radicle is present. The pedicel 
is narrow and about half the length of the scape. The first five flagellomeres are the 
smallest and, together, are about two times (2x) the length of the last three apical 
segments. First fiagellomere is the narrowest. The apices of the third to fifth 
flagellomeres are wider than their bases. The last three apical segments are widest in 
the middle and, together are longer than the scape. The last but one apical segment is 
evidently shorter than the club.
171
Plate 6.44: Schematic diagram of antenna of 
female A. reticulatus (x 90]
63.2.4 Muscoidea
Blepharella vasta (Karsh) (Tachinidae)
This is a big metallic green and black fly with a total body length of 12mm. It has red 
eyes (Plate 6.45) and the anterior abdominal segments are brownish, and the posterior 
ones black and bristly.
Plate 6.45: Blepharella sp. near vasta |x 3.8|
172
Peribaea orbata (Wiedemann) (Tachinidae)
These are small flies which are greyish black in appearance. They bear very stiff 
bristles (Plate 6.46) and have a superficial resemblance to the common housefly 
Musca domestica.
Plate 6.46: Peribaea orbata [x 15]
Discnssion
The parasitoid species identified and described from the Lepidopteran pests on 
cabbage in this study is a contribution to our understanding and documentation of 
African entomo-fauna and the parasitic Hymenoptera in particular. It is also a 
significant contribution to research in biological based control of the Lepidopteran 
pests of cabbage especially, P. xylostella in Ghana Out of the 15 species of 
parasitoids recorded, 7 were identified to the species level with 6 up to the generic 
level. Two were identified up to the species groups. Seven of the species: Charops
sp., Brachymeria sp., Hockeria sp., Elasmus sp., Notanisomorphella sp., Tetrastichus 
atriclavus S.L., Pediobius sp. and Trichomalopsis sp. have been recorded for the first 
time. The lengthy process of naming new species, which involves access to Type 
specimens and species, and all known species from other collections and museums 
has not enabled the species to be named in this study. Funds are being sourced to 
enable further studies to be carried out to name these species. Where possible, bar- 
coding (a new tool for identifying specimens) will be used as well as comparison with 
reference barcodes (Consortium for the Barcode of Life, 2009).
Apart from C. plutellae, all the other species are first records in Ghana. The 
identifications were either confirmed or determined at the British Museum of Natural 
History. United Kingdom and also the Systematic Laboratory of the United States 
Department of Agriculture, Gainesville in Florida. Some of the few existing 
descriptions and keys that were used were inadequate and as old as 90 years 
(Waterston, 1914; 1915 a & b; 1916; Ferriere, 1929; 1938; 1941). The fact that the 
specimens did not fit any of the species descriptions in the collections of the British 
Museum which holds the largest collection of Ghanaian specimens as well as from 
other parts of tropical Africa, the unavailability of keys for African species, and the 
inability of existing keys to key out the recorded species, support the proposal about 
the discovery of new species and buttress the importance of the information provided 
by the results of this study. Boucek (1988) observed that the minute size of the 
parasitic hymenoptera especially the Chalcidoidea makes their study unattractive. 
However, in Africa, the situation is particularly serious and acute due to lack of 
references on African entomo-fauna in general (Bio-Net INTERNATIONAL, 2006). 
Sometimes the problems encountered are due to inadequate descriptions without
174
illustrations and lack of access to Type materials (Boucek, 1988) or difficulty of 
identities of parasitoids (Waage and Greathead, 1986; Gupta, 1991; Smith et al., 
2008)
Colesia plutellae (formerly Apanleles plutellae), a Microgastrine Braconid, was 
originally described in 1912 by Kurdjumov from Plutella xylostella (Fitton and 
Walker. 1992) and Wilkinson (1939) re-described it. Mason (1981) recognised 
several new genera in the subfamily with the result that many species previously in 
the genus Apanleles have new generic assignments. Despite this, some authors have 
not accepted the new classification and still use the old generic name Apanleles sensu 
lato resulting in confusion in the literature (Fitton and Walker, 1992) and the potential 
of introducing more misidentifications in the literature. This study has given detailed 
morphological descriptions including scanning electron micrographs of characteristics 
of males and females of Cotesia plutellae in Ghana. Rincon et al. (2004) observed 
important morphological and genetic differences between populations and between 
males and females of different populations from different geographic areas. The 
descriptions provided in this study of the Ghanaian populations on cabbage will 
hopefully, help reduce this problem in Ghana. It will also contribute to a better 
understanding of the biology of Colesia species found on cabbage since the 
clarification of the identities of the different species is a key step in any biological 
study. The photographic descriptions and presentations can also be easily used as a 
guide in the field even by the non Taxonomist. The cosmopolitan species C. ruficrus 
(Haliday) occurs in parts of West Africa, but it is quite distinct from C. plutellae. It is 
also a gregarious parasitoid of internal and external hosts (Polaszek. et al.. 1994;
175
Walker, 1994), unlike C. plutellae which is solitary and does not parasitise internal
hosts. The other species, C.flavipes is known to occur only in East Africa.
Species o f Charops (Gupta and Maheshwary 1970; Maheshwary. 1971) have been 
recorded but none of these fit the description of the specimens recorded in the present 
study. Duodu and Lawson (1983) recorded C. diversipes Roman, in Ghana. 
However, other species previously recorded in Ghana were not available for 
comparison and other previous identifications were only up to the generic level.
The genus Brachymeria is relatively well known and most species are easy to 
recognize, based on the frequently yellow or white marked legs and tegulae. There 
are about 200 species worldwide and several are undescribed (Boucek, 1988). Keys 
to species have been provided for Europe, North America. India and the Oriental 
Region (Boucek, 1952; Burks, 1960; Narendra, 1989). Unfortunately, there are no 
keys to, or descriptions of African Brachymeria, making identification of species 
from this region difficult or even impossible (La Salle. CABI Bioscience U.K. pers. 
comm.). Boucek (1988) recorded B. marmonti (Girault) from Ghana
Waterston (1914), working on African Chalcidoidea described Hockeria munda sp 
nov. from Nyasaland, but the species observed in the present study is very different in 
body colouration, structure of wings, legs and antenna among others. The species on 
cabbage is similar to the Australian species H. dioculata (Girault) in having the post 
marginal vein very short. Hockeria Walker, 1834 is distributed in North America (5 
spp), Europe (about 10 species), Asia (about 20 species). Australia (3 species, only 1 
described) and in Africa at least 30 species but only 14 are described (Waterston.
176
1914, Boucek, 1988). The species described in the present study is a new record on 
cabbage in Ghana and may also be a new species to science.
Elasmus is the only genus generally recognised in the family Elasmidae though Riek 
(1967) established a second genus, based on differences in setal pattern of the meso- 
tibiae and meta-tibiae and relative length of sub-lateral scutellar seta. The family is 
sometimes classified as a subfamily of Eulophidae because of the structure of the pro- 
tibial spur. Members are also similar to some Aphelinidae (Eriaporinae) in the 
structure of the meta-coxa, meta-notum and in wing venation (Goulet and Huber 
1993). It is sometimes considered as a distinctive Chalcidoid family, principally 
because of its enormous flattened hind coxa (Burks, 1965). Burks (1967) 
classification is followed in this study. In addition, it is also distinguished by the 4- 
sgmented tarsi, female with only 3 funicular segments, the male with 4 funicular 
segments of which the basal one has lateral branches. However, these are also 
Eulophid characters and some authors recognize it as a subfamily of Eulophidae. 
Elasmus is widely distributed in the old world tropics but about 260,000 nominal 
species occur. Keys for species are available for Europe, North America, Asia and 
Africa, India and Australia (Ferriere, 1929; 1947; Burks, 1965; Riek, 1967). The 
species recorded in this study could not be identified by the key for the African 
species prepared by (Ferriere, 1929). This key is out of date and the species described 
here is likely to be new to science.
Members of the genus Euplectrus Westwood can be easily distinguished by the lack 
of sub-lateral grooves on the scutellum and the presence of a transverse carina at the 
anterior margin of the pronotum (Boucek, 1988). However, Zhu and Huang (2003)
177
indicated that the pronotal carina is not constant in this genus and that it aJso occurs in 
another genus thus, cannot be a good generic character. Nevertheless, this character, 
the fore-wing characteristics and features of the head and its appendages in the male 
and female given in this study can be used to easily determine E. laphygmae in 
Ghana. Ferriere (1941) gave a description of this species in Africa but with no record 
from Ghana. Zhu and Huang (2003) studied the genus Euplectrus in China and also 
obtained loans of specimens from the British Museum, Japan, Hungary and other 
places, but they indicated that the head of males of E. laphygmae in China are mostly 
dark while those from elsewhere are entirely yellow as was found in this study. These 
authors also listed the distribution of this species in West Africa and other parts of 
Africa but did not include Ghana. The record in this study makes it the first in Ghana 
and also the first parasitising Trichoplusia ni on cabbage.
Aphanogmus reticulatus is widely distributed and known only in Africa (Polaszek and 
La Salle, 1995; Polaszek, 1997). A. fijiensis (Ferriere) had been recorded on stem 
borers in Ghana by Polaszek and La Salle (1995) but this is the first time A. 
reticulatus has been recorded and characterized on cabbage. Females of the two 
species can be separated by the following: Middle club segment of female antenna 
evidently shorter than first club segment and head broader in facial view in A 
reticulatus than in A. fijiensis. Clypeus broadly truncate, medially with lateral 
extensions in A. reticulatus. In A. fijiensis. middle club segment equal to first club 
segment, head narrower in facial view and clypeus pointed medially without lateral 
extensions.
178
Nolanisomorphella Girault has three synonyms; Crateulophus Masi, 1917; Rauruna 
Risbec. 1952; and Sunha Delucchi 1962 (Goulet and Huber 1993). The genus was 
synonymised under Sympiesis Forster by Girault (1917) and treated as such by 
subsequent authors (Boucek. 1988). This author, however, regarded it as a separate 
genus and distinguished Nolanisomorphella by the presence of irregularly step-like 
but distinct plicae. This classification and distinction is used here. Boucek (1988) 
recognised two species groups (proserpinensis and flaviventris) based on the nature of 
the propodaeum. The specimen described here falls in the flaviventris group 
(propodaeum punctured-reticulate) and may also be a new un-described species.
Until 1957, Oomyzus was regarded as one of the synonyms of Tetrastichus sensu lato 
(Boucek, 1988). The current definition of this genus is given by Graham (1969 and 
1987). The main features are: short black body with a distinct metallic tin t female 
flagellum stout, with funicular segments sub-quadrate (almost as long as wide), the 
male flagellum with whorls of setae and propodaeum not short. Boucek (1988) noted 
that members often have weak sub-median grooves on the scutellum. The species 
recorded here O. sokolowskii, however, has a strong sub-median scutellar groove. 
The main difference between O. sokolowskii and Tetrastichus atricalvus s.l. also 
recorded in this study is that the antenna of the female of the latter species is paler, 
longer and not stout, eyes are bigger, body more elongated and streamlined. Other 
differences are in the colouration of legs, dorsum of metasoma more flattened and 
posterior end more elongated. Antenna of male T. atriclavus s.l is also black and 
lacks the whorls of setae present in (). sokolowskii. Fore coxae arc lighter in colour. 
However, some specimens varied in this lust character.
179
Pediobius has been known for almost a century under the name Pleurotropis Foerster, 
1856. and a large amount of literature is available under this name (Kerrick, 1973). 
However, in 1953, Ferriere established Pediobius Walker 1846 as the senior synonym 
(Burks. 1966; Kerrick, 1973). Waterston (1915) defined and characterised this genus 
and his views are still accepted. There are several keys to species of regional faunas: 
Europe (Boucek, 1965; Graham, 1969; Dawah, 1988); North America (Burks, 1966; 
Peck. 1985); tropical and subtropical Africa and Asia (Kamijo, 1986). Distribution of 
this species is worldwide with over 100 species, but Africa appears to be the centre of 
origin and contains the greatest number of species (Kerrick, 1973). Waterston (1915) 
and Masi (1940) cited in Boucek (1988) laid the basis for our knowledge of the 
African species. Kerrick (1973) determined species associated with the oil palm 
hispid Coelaenomenodera elaeidis Walker, for field entomologists in West Africa. 
He recorded and described eight species from Ghana but he indicated that a lot 
remains to be described.
Most species of Trichomalospsis are known from Holarctic and Oriental Regions 
(Graham, 1969). Species from rice paddies have been revised by Kamijo and Grissell 
(1982).
Blepharella sp. near vasta (Karsch) belongs to the family Tachinidae. This large 
genus badly needs revision and the specific name could not be determined for the 
specimens collected in the present study (Wyatt. NHM. United Kingdom. Pers. 
Comm.).
180
The parasitoids and hyperparasitoids recorded in this study are first records on 
cabbage in Ghana. Most of the existing descriptions are vague, and due to the paucity 
of information, lack of expertise and the out-of-date keys, some could not be 
identified to species level. No access could be obtained to examine type specimens. 
In addition, the species of parasitoids already recorded in Ghana were mainly from 
stem borers and most are of uncertain identity (Polaszek and La Salle, 1995).
181
CHAPTER SEVEN
7.0 GENERAL CONCLUSIONS AND RECOMMENDATIONS
7.1 Conclusions
The dominant parasitoids and the major Lepidopteran pests on cabbage in Ghana have 
been identified. The parasitoid-host relations were; C. plutellae which parasitised P. 
xylostella, T. ni, S. littoralis and H. undalis, and E. laphygmae which parasitized T. ni 
and S. littoralis. Cotesia plutellae however, had a preference for P. xylostella.
There was seasonality in the occurrence and abundance of the pests. During the dry 
season (February - March) P. xylostella was the most abundant pest but, Hnring the 
major rainy season (May - July), T. ni was more abundant. However, P. xylostella 
was the more important pest and occurred in significant numbers in all three seasons. 
The dry season was the worst time to grow cabbage due to the high incidence and 
infestation of P. xylostella. However, in areas where cabbage was grown for the first 
time under the Farmer Field Schools Programme in 1999 - 2001 and in some villages 
located near the Homasi concession of Anglogold, Ashanti Ghana Ltd. in the Amansie 
Central District in the Ashanti Region in 2008, P. xylostella was absent. Trichoplusia 
ni and S. littoralis may also be damaging to cabbage in the major and minor rainy 
seasons respectively as they occurred in abundance. Similarly, Helicoverpa armigera 
and H. undalis, even though, occurred in very small populations could be destructive 
due to the fact that they feed on the growing points of cabbage.
The most important parasitoid associated with the major pest was Cotesia plutellae
which is a solitary endo-larval species and it occurred in all three seasons. C.
182
plutellae acted in a density dependent manner in relation to its hosts, thus, parasitism 
increased as host numbers increased. This should make it a good candidate in the 
development of an Integrated Pest Management Programme for control of its hosts on 
cabbage. However, this parasitoid appeared late in the season when pest populations 
had already built up. Hence in the dry season when high infestations of P. xylostella 
are expected this parasitoid may not be available in sufficient numbers to be effective. 
An intervention early in the season, possibly an augmentative release of C. plutellae 
at 25 days after transplanting could reduce pest numbers to counteract the effect of the 
initial time lag by this parasitoid.
Euplectrus laphygmae is a gregarious ecto-parasitoid species and occurred in the 
major and minor rainy seasons. Its specificity to mature larvae of Trichoplusia ni and 
S. littoralis undoubtedly makes it also a parasitoid that must be considered in the 
development of any management strategy of these pests on cabbage.
Oomyzus sokolowskii and Trichomalopsis sp. are also important parasitoids/ 
hyperparasitoids of P. xylostella on cabbage in Ghana. The six species of parasitoids 
(Blepharella vasta, Peribaea orbata, Chelonus curvimaculatus, Euplectrus 
laphygmae, Charops sp. and Notanisomorphella sp.) recorded from S. littoralis 
caused insignificant amount of parasitism and may not be important mortality factors 
for this species.
The total contribution of all the parasitoid species however, could be significant in 
keeping the cabbage pest populations down.
183
No egg parasitoids were observed in this study. Eight of the Hymenoptera parasitoid 
species recorded in the following genera: Charops, Elasmus, Hockeria, Brachymeria, 
Pediobius, Tetrastichus, Nolanisomorphella, and Trichomalopsis in this study, are 
first records on cabbage in Ghana and likely to be new species.
Cotesia plutellae undoubtedly, play an important role in the natural and biological 
control of P. xylostella and T. ni, but indiscriminate use of insecticides could reduce 
their effectiveness. The pyrethroid, Karate (a common insecticide used by Ghanaian 
fanners) was directly and highly toxic to C. plutellae as it caused 100% mortality in 
the adults within ten seconds of direct exposure. Karate also caused indirect toxicity 
as it killed the adults in the process of eclosion or reduced their longevity. It could 
therefore, reduce the effectiveness of C. plutellae by eliminating them, reducing their 
fecundity and fitness or causing a decrease in the numbers that will be available to 
sustain succeeding generations of the parasitoids. This adverse effect on such an 
important parasitoid has severe implications on the continued use of Karate by 
Ghanaian farmers. These results suggest that in the development of an Integrated Pest 
Management (IPM) programme that will include the use of C. plutellae, Karate 
should not be included. Bacillus thuringiensis may be a better alternative as it caused 
less mortality to the adult parasitoid. Lower concentrations of neem seed extracts 
could be investigated in a biological based control programme of pests on cabbage, as 
Neem seed water extract at 50 g/1 and Neemazal at 1.0 ml/1 adversely affected 
metamorphosis in C. plutellae.
The present study has for the first time, generated new and useful information on the 
identity, description, biology, illustrations, seasonal occurrence and distribution, of
184
the important parasitoids and their hosts on cabbage in Ghana. It has also provided 
new evidence on the toxicity of the commonly used insecticide (Karate), and neem 
products at certain concentrations to the most important parasitoid of the major pest, 
P. xylostella. The practical relevance of this information to producers is the 
application of this knowledge in the correct timing of planting for sustainable 
production and reduction in insecticide use and thereby, reduce costs and protect the 
major parasitoids and health of consumers of cabbage in Ghana.
The results of this study are significant to African entomo-fauna in general and on 
cabbage in Ghana in particular. Even though the identification and descriptions of the 
parasitoids have been worked out in this study, it was a daunting task due to lack of 
previous research and expertise in this area, the unavailability and out-of-date 
literature on African Hymenoptera, especially Ghanaian species.
U Recommendations
From the results of the present study, the following recommendations are made:
1) Further studies involving the examination of type species and other collections 
are needed to confirm the status of the proposed new species of parasitoids 
observed in this study.
2) Even though, egg parasitoids were not found in this study, species of 
Trichogramma have been recorded as egg parasitoids in some other places 
outside Ghana. This is an area that requires further investigation in Ghana.
3) The high rales of parasitism by C. plutellae of its hosts on Karate treated plots, 
as well as the longevity and competitiveness of adults of the parasitoid
185
emerging from pupae exposed to the insecticide, are worth investigating and 
also determining the insecticide resistance status of the parasitoid.
4) There is the need for studies to determine the most appropriate times and 
method of application of B. thuringiensis in an IPM programme on cabbage in 
Ghana. Lower doses of neem should be investigated to determine the 
appropriate rates in order to conserve the dominant parasitoid, C. plutellae.
5) It is advocated that more surveys and research on the parasitoids should be 
carried out to facilitate documentation of the local fauna and to reduce reliance 
on the use of pesticides.
6) Production of Field guides of the parasitoids and their hosts on cabbage would 
greatly contribute to the usefulness of the results of this study. Documentation 
of the fauna is what all decisions regarding conservation and exploitation of 
biological resources depend on.
186
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APPENDICES
APPENDIX 3.1
Towns where cabbage was grown for the first time in 1999-2001 or 2008
Region/Town(s) P. cheiranthei H. undalis
GREATER ACCRA
Dodowa +
Moyose + -
EASTERN
Donkorkrom - +
Amankwa Tano +
WESTERN
Suiano + -
Denche/Moasue + -
Senyaguakrom + -
‘ASHANTI
Prago - +
*Cabbage grown for first time in 2008 
+ Means present 
- Means not present
224
APPENDIX 3.2
Total Numbers of C. plutellae pupae collected from the different 
plots exposed to insecticides in the field.
Treatment
Major rainy season Dry season
Total no. of pupae Total no. of pupae
Unsprayed 194 178
Bt 94 160
Karate 518 828
NSWE - 177
Total 806 1343
APPENDIX 3.3
Percentage emergence of C. plutellae adults collected as pupae 
exposed to different insecticides in the field
Species Major rainy season (N=865) Dry season (N=1302)
C. plutellae 84.0 95.2
A. reticulatus 6.35 -
Trichomalopsis sp 8.20 4.1
Others 1.41 0.7
225