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QL537. C46 
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G360923 iBThe Bialmie Liibrariy a
3 0692 1078 5425 7
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INSECTS ASSOCIATED WITH CITRONELLA 
IN SOUTH-EASTERN GHANA, WITH PARTICULAR 
REFERENCE TO SHOOTBORERS
by
JOSEPH EASMON SARFO 
B.SC. (HONOURS) CAPE COAST (1984) 
DIP> EDUC. CAPE COAST (1984)
A thesis submitted to the Department of Zoology, Faculty of 
Science, in partial fulfilment of the requirements for the degree of 
MASTER OF PHILOSOPHY of the UNIVERSITY OF GHANA
September, 1993.
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To
Maame Yaa Boatemaa Sarfo 
And
Nana Akua Sarfowaa Sarfo
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ZOOLOGY DEPARTMENT 
UNIVERSITY OF GHANA 
LEGON
This is to certify that this thesis has 
not been submitted for a degree to any 
other University. It is entirely my 
own work and all help has been duly 
acknowledged.
Supervisor
(Dr. S.Q. Quartey)
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A CKNO WLED GEMENTS
I would like to express my sincere gratitude to my principal supervisor, Dr. S.Q. 
Quartey for his patience, useful criticisms and suggestions. My sincere thanks are due to 
Miss Cobblah of Zoology Department, a supervisor, who helped in the identification of 
some insects and also made available to me some useful printed materials. I am very 
grateful to Mr. Deeming (British Museum) for identifying the Chloropidae and 
Lonchaeidae and for providing me with key for the identification o f shootflies. I would 
also like to thank Dr. C.Y. Brempong-Yeboah of Crop Science Department, Faculty of 
Agriculture, who as a supervisor, enthusiastically and readily offered assistance whenever 
consulted. My sincere gratitude also goes to Dr. J.B. Ackonor (Cocoa Research Institute 
of Ghana -  CRIG) for patiently reading through the re-written script and making very 
useful suggestions. I thank Dr. N.N.N. Nuamah (ISSER, Legon) and Mr. Ken Brew 
(CRIG) for helping with some statistics. I am also grateful to Dr. (Mrs.) Botchwey and 
Mr. P. Kwapong (University of Cape Coast) for providing me with very useful printed 
material.
I appreciate greatly, the concern expressed by the Professors and lecturers of 
Zoology Department, especially about the delay of the work. I am particularly grateful to 
Dr. Wilson and Prof. Coker for their usefid suggestions. To the technicians of Zoology 
Department, especially Mr. Titiati, Mr. Ofosu Baako, Mr. Asiedu and all others, I say a 
big thank you for your patience and immense technical help.
I am greatly indebted to Kwesi of Osofoiaman, Dr. Tagoe, Madam Selina Taylor, 
Mr. Ababio and all the other farmers who allowed me to use their farms for the study.
Mr. Vincent Acheampong (University of Ghana, Academic Affairs), Mr. F. 
Aneani (CRIG), Mr. Kwame Vowotor (Food Research Institute) and Mr. Alfred Quartey 
(University of Ghana, Data Processing Centre) deserve special mention. They, despite 
the inconvenience to them, stayed for long hours and sometimes late to help me with 
most of the analysis of my data and the processing of my graphs. I also thank Willie of
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Survey Department, Accra, for his neat cartographic work. I appreciate very much the 
photographs on the grass-hoppers taken by Mr. & Mrs Effah-Bekoe of Amsterdam, 
Holland. I am very grateful to Mr. Williams and my colleagues, Mr. Carl Fiati and Mr. 
Owusu-Boateng for their encouragement especially at difficult times. My special thanks 
go to another colleague, Mr. Albert Addo Kwafo, Faculty of Agriculture, for coming to 
my aid by offering me accommodation at a very critical time and also for the other 
numerous acts of kindness which helped me a great deal in getting this work completed.
I am very grateful to my friends, Mr. Peter Opoku, Survey Department, Accra, 
and Mr. Paul Forson of K.Y. Merchants, Accra, for the numerous valuable assistance 
given in diverse ways to make this work a possibility.
My warmest thanks go to Miss Mercy Techie-Menson, Miss Bertha Afful, Miss 
Theodora Mifetu, Miss Akosua Henewaa Dapaah, Miss Suzzy Micah and Miss Joyce 
Anane for their encouragement, company and friendship.
Finally, I thank Miss Grace Acheampong (University of Ghana, Academic 
Affairs), Mr. Kwame Amoako and Mr. Michael Doe Kulogo (CRIG) for accepting to 
neatly type this work and patiently doing all corrections when they had other pressing 
commitments.
J .E S
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ABSTRACT
Insects associated with citronella were surveyed in the south-eastern part of 
Ghana for 11 months. Using two different sweep nets, intensive and extensive surveys 
showed that the foliage of citronella was associated with a diverse insect fauna 
comprising 10 orders and 102 families as follows: Hymenoptera (29), Diptera (32), 
Homoptera (8), Hemiptera (12), Coleoptera (10), Dictyoptera (2), Orthoptera (3), 
Lepidoptera (2), Dermaptera (1), and Neuroptera (3).
The shoot of citronella was found to be damaged by dipterous shootflies (Fam: 
Chloropidae and Fam: Lonchaeidae) and lepidopterous stemborers (Fam: Pyralidae and 
Fam: Noctuidae). There was no significant difference (P > 0.05) between the mean 
percentage infestation by the shootflies (mean =1.18%) and that o f the stemborers (mean 
= 0.59%). The chloropid shootflies were identified as Scoliophthalmns micantipennis 
Duda, Scoliophthalmus trapezoides Becker, Anatrichus pygmaeus Loew, Aprometopis 
flavofacies Becker, Elachiptera occipitalis Becker, and unidentified species. The 
lonchaeid shootfly was Silbapectita McAlpine. The pyralid and noctuid stemborers were 
Eldana saccharina Walker and Sesamia sp, respectively. Whereas S. micantipennis, A. 
flavofacies were found to cause primary damage by attacking fresh stems, S. trapezoides 
caused both primary and secondary damage by attacking fresh as well as already infested 
stems. The status of the other chloropids and the lonchaeid was not clear, since they were 
always found in association with other insects in already infested tillers. The 
lepidopterous stemborers were also found to cause primary damage. The larvae of the 
stemborers attacked the lower part of the tiller and tunnelled a length of 75.40 ± 12.79 
mm while the shootflies tunnelled 32.60 ± 3.90 mm. The larvae live inside the tillers and 
so can possibly be controlled by systemic inseticides.
Preliminary field investigation showed that the worker caste of unidentified 
termites attacked the roots and stems of citronella, and this invariably led to complete 
death of the plant. This was more prevalent in farms older than one year; for example,
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85.7% of the termite infested farms were older than one year. Farmers should therefore 
not cultivate one farmland for too long. Further investigations showed negligible 
symptoms of feeding activities of insect foliage pests. For example, less than 0.005%,
0.002% and 0.009%, showed necrosis, curling and defoliation respectively, from insect 
attack in any farm.
Investigation of the seasonal variation of shootborer infestation of citronella 
showed two possible peaks: one between February and March, and another around 
October for both the lepidopterous stemborers and chloropid shootflies. The 
synchronisation in the build up of the damage by both groups o f shootborers shows that 
they can be controlled simultaneously. Percentage 'deadheart' caused by lepidopterous 
stemborers had a weak linear relationship with rainfall: y = 0.0017x + 0.6298. That by 
the dipterous shootflies also had a weak linear relationship with climatic factors as 
follows:- rainfall: y = -0.0024x + 1.3413; evaporation: y = -0.8958x + 2.2639; 
temperature: y = -0.5826x + 17.15; and relative humidity: y = 0.1292x - 9.8968; where y 
= percentage deadheart' and x = climatic factor.
Comparision of sampling, using only visual 'deadheart' symptom and 
random dissection, showed that using only 'deadheart' symptom underestimated the 
infestation of shootborers by 31.8%. Shootborer infestation should therefore be 
determined from random dissection of tillers.
The pupa of female S. micantipennis measured 3.32 + ,08mm in length (n=30) 
and pupal period averaged 6.72 + 0.39 days (n = 22). The male pupa measured 3.16+_.07 
mm long (n = 30) and the mean pupal period was 7.24 + 0.05 days (n = 17). The adults 
of both sexes lived for about the same period: 8.59 + 0.77 days (n = 29) for the female 
and 9.41 + 0.60 days (n = 24) for the male. The adults exhibited sexual dimorphism with 
respect to their total body lengths, the male being shorter (1.90 ±  0.02mm; n = 30) than 
the female (2.98 + 0.03mm; n = 31).
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TABLE OF CONTENTS
Declaration........................................................................................ iii
Acknowledgements.......................................................................... iv
Abstract............................................................................................. vi
List of Figures.................................................................................. xi
List of Tables.................................................................................... xiii
List of Plates...................................................................................... xiv
GENERAL INTRODUCTION AND LITERATURE REVIEW 1
General Introduction........................................................................ 1
Introduction of Citronella in G hana............................................... 1
Citronella farming in Ghana.......................................................... 2
Why this study ................................................................................. 4
Literature review.............................................................................. 6
The Citronella plant.......................................................................... 6
Importance of Citronella.................................................................. 7
Insect interactions with the Poaceae in general............................ 8
Insect pests of Citronella................................................................. 9
INSECTS ASSOCIATED WITH CITRONELLA....................... 11
Introduction....................................................................................... 11
Materials and methods.................................................................... 11
Sampling Points and C lim ate......................................................... 11
Sampling procedures........................................................ 15
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2.2.2.1 Insects on citronella shoot (leaves and stems)............................................................
2.2.2.2 Insects (pests) damaging citronella  16
2.2.2.3 Comparison of the Efficiencies of the Improved and Standard Sweep nets  19
2.2.2.4 Comparison of Sampling methods  19
2.3 Results  23
2.3.1 Insects on citronella shoot (leaves and stems)................v   23
2.3.2 Insects damaging citronella  24
2.3.3 Comparison of the Efficiencies of the Improved and Standard Sweep nets............ 26
2.3.4 Comparison of Sampling methods.............................................................................  27
2.4 Discussion.................................................................................................................... 35
3.0 INSECT PREFERENCES FOR DIFFERENT SIZES OF HOST 
PLANT AND NATURE OF SHOOTBORER DAMAGE TO THE
SHOOT OF CITRONELLA....................................................................................... 42
3.1 Introduction...............................................................................................................  42
3.2 Materials and Methods.............................................................................................  43
3.2.1 Field investigation of preference for size of Citronella tillers by shootborers......... 43
3.2.2 Boring activity of the shootborers................................................................................  43
3.2.3 Field Identification of damage from differential growth (height) of newly 
ratooned infested and uninfested tillers........................................................................ 44
3.3 Results............................................................................................................................ 46
3.3.1 Field investigation of preference for size of Citronella tillers by shootborers.......  46
3.3.2 Boring activity of the shootborers.................................................................................  46
3.3.3 Field identification of damage from differential growth (height) of newly 
ratooned infested and uninfested tillers........................................................................ 47
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Discussion............................................................................................................. 51
SEASONAL VARIATION IN INFESTATION OF CITRONELLA BY 
LEPIDOPTEROUS STEMBORERS AND CHLOROPID SHOOTFLIES .. 54
Introduction........................................................................................................... 54
Materials and methods........................................................................................... 54
Determination of Sample size and measurement of Incidence of 'deadheart’ 
caused by shootborers........................................................................................... 54
Rainfall, Temperature, R.H. and Evaporation.................................................... 56
Results..................................................................................................................... 56
Determination of Sample size and measurement of incidence of'deadheart’ 
caused by shooborers........................................................................................... 56
Rainfall, Temperature, R.H. and Evaporation................................................... 58
Discussion.............................................................................................................. 67
ASPECTS OF THE BIOLOGY OF SHOOTFLY, SCOLIOPHTHALMUS 
MICANTIPENNIS (DIPTERA: CHLOROPIDAE)........................................... 70
Introduction........................................................................ ;.................................. 70
Materials and methods.......................................................................................... 70
Results.................................................................................................................. . 74
Discussion............................................................................................................. . 80
SUMMARY AND CONCLUSIONS.................................................................. 82
Summary................................................................................................................. 82
Conclusions............................................................................................................ 83
REFERENCES............................................. 85
APPENDICES 91
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LIST OF FIGURES Page
Figure 1: Map of Southtem Ghana showing locations where sampling was done ............. 13
Figure 2: The standard and improved sweep nets.................................................................. 22
Figure 3: Infestation rates as determined by only 'deadheart' symptom and by
Random dissection.................................................................................................... 28
Figure 4: Dorso-Iateral view of female Scoliophthalmus trapezoides..............................  29
Figure 5: Dorso-lateral view of female Scoliophthalmus micantipennis..........................  30
Figure 6: Lateral view of female Anatrichus pygmaeus........................................................  31
Figure 7: Dorso-lateral view of female Aprometopis flavofacies......................................  32
Figure 8: Lateral view of female Elachiptera occipitalis.................................................... 33
Figure 9: Longitudinal section of tiller attacked by lepidopterous stemborer........................ 48
Figure 10: Longitudinal section of tiller attacked by shootfly./............................................  49
Figure 11: Daily growth of healthy and infested tillers of ratooned citronella at
Osofoiaman in one week in 1991.........................................................................  50
Figure 12: Percentage 'deadheart' caused by shootflies and lepidopterous stemborers,
Osofoiaman Farm B, 1991................................................................................  59
Figure 13: Percentage 'deadheart' caused by shootflies and lepidoperous stemborers,
Osofoiaman Farm A, Jan - June, 1991................................................................ 60
Figure 14: Mean monthly rainfall, evaporation, relaltive humidity, temperature and 
percentage 'deadheart' by shootflies and lepidopterous stemborers,
Osofoiaman, Farm B, 1991...................................................................................  61
Figure 15: Relationship between percentage 'deadheart' by stemborers and rainfall....... 62
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Figure 16: Relationship between percentage 'deadheart' by shootflies and rainfall............  63
Figure 17: Relationship between percentage 'deadheart' by shootflies and evaporation....... 64
Figure 18: Relationship between percentage 'deadheart1 by shootflies and temperature....... 65
Figure 19: Relationship between percentage 'deadheart1 by shootflies and relative humidity 66 
Figure 20: Dorsal view of male puparium of Scoliophthalmus micantipennis with the tip
broken to provide passage for the emerging adult...........................................  77
Figure 21: Dorsal view of female puparium of Scoliophthalmus micantipennis with the
tip broken to provide passage for the emerging adult....................................... 78
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LIST OF TABLES Pag£
Table 1: Foliar damage by insects to citronella leaves in different farms..........................  24
Table 2: Adult Diptera reared, and Lepidoptera larvae collected, from tillers showing
'deadheart' symptoms from Osofoiaman and other farms in 1991...................... 25
Table 3: Incidence of termites in sampled farms, in Greater Accra Region, 1991............  26
Table 4: Analysis of twenty (20) samples of insects each by improved and standard sweep
nets, at 10 sweeps per sample................................................................................... 27
Table 5: Summary and analysis of tillers preferred and damaged by the shootborers....... 47
Table 6: Survival and Development of larvae of shootflies collected from infested tillers 75
Table 7: Length of empty puparia of female and male Scoliophthalmus micantipennis.... 76
Table 8: Pupal period of male and female Scoliophthalmus micantipennis in the laboratory
at 27.4°C................................................................................................................  76
Table 9: Longevity of adult male and female Scoliophthalmus micantipennis in the
Laboratory at 27.4°C........................................................................................... 79
Table 10: Total body length of adult male and female Scoliophthalmus micantipennis...... 79
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LIST OF PLATES Page
Plate 1: Citronella farm..................................................................*..................................... .......... 3
Plate 2: Rearing of insects from cut citronella shoots........................................................  21
Plate 3: Zonocerus variegatus attacking citronella on the farm.......................................  34
Plate 4: Experiment to study the boring activity of shootfly larvae..................................  45
Plate 5: Experiment to determine oviposition site of Scoliophthalmus micantipennis
in the laboratory.........................................................................................................  73
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CHAPTER ONE
1.0 GENERAL INTRODUCTION AND LITERATURE REVIEW
1.1 General Introduction
1.1.1 Introduction of Citronella in Ghana
Citronella is an essential oil producing Poaceae (Gfaminae) with origins in Asia. It is 
however, now cultivated in many tropical and subtropical areas such as Taiwan, Malaysia, Sri 
Lanka, Indonesia, Seychelles Islands, Zaire, B razil, Uganda (Skerman and Riveros, 1990). 
The two main species, Cymbopogon nardus and Cymbopogon winterianus, have been 
cultivated in Ghana since 1978 (Laryea, 1988).
Citronella was introduced in Ghana from Sri Lanka by Lever Brothers Ghana Limited 
(LBG) in 1978 through Dr. David Tagoe, the then Technical Services Manager of LBG, to 
produce citronella oil locally for the company’s soap manufacturing industry. A few tillers 
each of the following five types of Cymbopogon were introduced;
i. Cymbopogon nardus
ii. Cymbopogon winterianus
iii. Citronella variety Number one
iv. Lemongrass ex Sri - Lanka 
v. East Indian Lemongrass
Initial agronomic studies at the University of Ghana showed that it was feasible to 
cultivate all the five types in Ghana. LBG, however, preferred the citronella to the lemon grass 
because it had a higher yield of oil and therefore it was of better commercial value. In 
1981, LBG’s first attempt at cultivating citronella in a pilot scheme at Banso in the Western
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Region failed because of poor soil condition due to high acidity, high incidence of stemborers 
and rust infection at the site (Laryea, 1988).
LBG attempted another pilot project at Bunso in the Eastern Region in 1982. This was 
successful and the farm served as the source of planting material for many outgrowers. As at 
1989 there was a total of 46 farms of citronella spread over Brong Ahafo, Ashanti, Western, 
Eastern, Central, Greater Accra and Volta regions (Laryea, personal communication). The 
farmers formed an association known as Citronella Oil Producers Association (COPA), and 
they are the core of citronella producers in Ghana. .According to Laryea (Personal 
communication), their number as at 1992 had risen to just over 50 with farms covering over 
200 ha from which about 10,000 kg of oil was being produced annually. The number of 
farmers could have been higher but for the ceiling put on COPA membership by LBG. There 
are numerous small scale citronella farmers outside COPA.
1.1.2 Citronella Farming in Ghana
Citronella is currently cultivated countrywide except in northern Ghana. According 
to LBG, sandy loam with fairly distributed annual rainfall of over 900mm is the most preferred 
condition for the cultivation of citronella. The most suitable time for planting is at the onset 
of the rains. The planting material is at least a 6-month old tiller pruned of the leaves and 
roots. The tillers are planted about 8 to 10cm deep in the soil and spaced about 60cm, giving 
about 27,000 tillers per hectare. Time and frequency of weeding is determined by the farmer. 
Good husbandry requires that flowers from citronella should be removed since flower 
production depletes the oil content of the plants. Harvesting of citronella leaves is done when 
the leaves become mature at which stage the tips become dry and curl backwards. In times
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Plate 1: Citronella Farm
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of adequate rainfall, this is about 6 months after planting and subsequent harvests are done at 
3-4 month intervals or shorter.
Harvested citronella is dried in the field for about 4 days to reduce the water content 
and also to reduce the load on the still. Harvesting is therefore not recommended during the 
very wet periods since the leaves rot during drying. Dried citronella is cleaned of moulds and 
other foreign bodies before being distilled by steam.
1.1.3 Why this Study
One of the reasons for the failure of the first citronella pilot programme at Banso in 
1981 was stemborer attack. Also in 1988, a team from the University of Ghana reported 
lepidopterous stemborer attack and possible leaf hopper damage at Ayikuma in the Greater 
Accra Region. According to the report, damage by the insects was so serious at Ayikuma and 
some areas in the Greater Accra region that severe crop losses and revenue were recorded. 
There is also the fear that since citronella is cultivated as a monocrop, the insect pest problem 
will become more serious as cultivation increases.
Apart from the initial investigations, no detailed study has been done on the pest and 
disease problems of citronella. This study is, therefore, aimed at providing a more detailed 
information about the insects associated with citronella, and to study the ecology and biology 
of the major pest(s), with a view to providing baseline information that will be useful in 
designing an ecologically acceptable and economically feasible pest management programme 
for the citronella cultivation in Ghana.
The objectives of the study are, therefore,
i. to collect and identify all stages of insects associated with citronella in south
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- eastern Ghana,
to identify the major and potential insect pests and their natural enemies, when 
possible,
to determine insect pest preferences for different sizes of host and to 
characterize the nature of pest damage,
to study the seasonal trends of infestation of the major insect pests of citronella 
to determine the effects of relative humidity (R.H.), evaporation, temperature 
and rainfall on the infestation of the major insect pests of citronella and 
to study the biology of the major insect pest(s) of citronella.
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1.2 Literature Review
1.2.1 The Citronella Plant
Citronella is a perennial grass and it is classified as follows :
Family : Poaceae (= Graminae)
Subfamily : Panicoideae 
Tribe : Andropogoneae
Genus : Cymbopogon
The genus Cymbopogon has about 60 species (Purseglove , 1983) which give varied products 
including essential oils, fodder, mulch and thatching material (Bor, 1960; Arber, 1965; 
Purseglove, 1983; Skerman and Riveros, 1990; Bajracharya, 1990; Singh et al, 1991). The 
species include Cymbopogon nardus (Rendle - Ceylon/Sri Lankan type) and C. winterianus 
Jowitt - Java type which produces citronella oil ( Wijesekera, 1973), C. citratus (DC) Stapf, 
which produces lemon grass oil (Arber, 1965) and C. martinii (Roxb) Wats which gives 
palmrosa oil (Bor , 1960 ).
Citronella grows in tufts and at maturity, the height varies from about 0.5 to lm. The 
plant consists of tillers which vary from two to over a hundred, depending on age and variety. 
A tiller consists of a short rhizome, made up of a series of nodes separated by short intemodes 
and relatively long sheaths crowned by long narrow leaves. The basal nodes are very close 
together and the lowest nodes normally give rise to the roots.
The morphological differences between C. nardus and C. winterianus lie in the shape 
of their leaves which, according to Senaratne (1956); are narrower in C. nardus. 
Cymbopogon nardus is hardier than C. winterianus and while the former can thrive even on
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marginal soils and produce for 10 to 15 years, the latter thrives only on well drained sandy 
loam with abundant rainfall and can produce for only three to four years (Laryea, 1988). The 
chemical difference between the two species is found in the citronellal component of the oil 
(Wijesekera, 1973). Thus, C. winterianus contains more citronellal (32.7%) than C. nardus 
(5.2%).
1.2.2 Importance of Citronella
Citronella plants are cultivated for their extensively used essential oils, which are 
mainly terpenes such as geraniol, citronellal and citronellol. The most important oils produced 
are citronella oil from C. nardus and C. winterianus (Bor , 1960); lemon grass oil from C. 
citratus (Aber, 1965); and palmrosa oil from C. martinii (Bor, 1960).
According to Wijesekera (1973), citronella oil is used in perfumes; as deodorants in 
mosquito repellants, insecticides, soaps, disinfectants, paints and polishes. It is also used in 
the preparation of aromatic chemicals derived from citronellol and geraniol. Citronella oil also 
has great potential in pest control, for it repels stored product pests, such as Tribolium 
castaneum (Hbst)(Coleoptera: Tenebrionidae) and Bruchus chinensis (L.) (Coleoptera: 
Bruchidae), as well as Periplaneta americana (L.) (Dictyoptera: Blattidae) (Saraswathi and 
Rao, 1987). The oil may also inhibit fungal growth and spore gennination (Raghavaiah and 
Jayarmaiah, 1987). In Ghana, Lever Brothers Ghana Limited (LBG) uses citronella oil to 
perfume the following brand soap products: KeyR soap, Sunlight11 soap, and GuardianR soap. 
Lemon grass oil is used in the commercial synthesis of vitamin A and also in scenting soaps, 
while palmrosa oil is acclaimed to be the best natural source of geraniol used as a soap 
perfume and also for the flavouring of tobacco (Purseglove, 1983).
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Other products of citronella are also useful. For example, water extract from C. 
flexuosus is a nematicide that suppresses root knot development in tomato and aubergine 
caused by Meloidogyne incognita (Tiyagi et al, 1990), leaves of C. nardus are used as mulch 
and as a thatching material (Skerman and Riveros, 1990) whereas the spent grass o f C. 
flexuosus is used as fodder (Bajracharya, 1990).
1.2.3. Insect interactions with the Paaceae in general
Citronella belongs to a family of pants (Poaceae) which play host to numerous insects, 
consisting of plant feeders, predators, parasitoids and casual visitors (Tams and Bowden, 
1953; Ingram, 1958; Nye, 1960a; Harris, 1962; Watts, 1963; Byers, 1967; Deeming, 1971). 
The age, morphological features, texture, turgidity and manner of growth of the plant are 
among the factors that influence insect attack of the group (Wiliams, 1954; Mulkem, 1967; 
Easwaramoorthy and Jayaraj, 1988). Shootborer activity on poaceous plants also tend to 
fluctuate under the influence of several extraneous factors including the following, wet and 
dry seasons (Sarel-whitfield, 1929; Rose, 1973; Wilson et al, 1973), cropping seasons (Harris, 
1962; Endrody-Younga, 1968; Girling, 1978) and weather and climate (Smithers 1960; Harris, 
1962; Adeyemi, 1969; Barry, 1972; Balraj et al, 1977; Clearwater and Otieno, 1977; Ogwaro, 
1979), as well as farming practices (Harris,1962; Girling,1978) and altitude (Ingram, 1958; 
Nye, 1960b; Reddy, 1982).
Insect attack on the family produces several damage symptoms such as 'white head’ 
and 'deadheart’ (Nye, 1960a; Deeming, 1971; Agen-Sampong, 1975), gouted shoots 
(Goodlife, 1942) and wilted shoots (Simmonds, 1952). It may directly result in decrease in 
yield (Poos and Johnson, 1936; Wolfenbarger, 1963; Peterson and Granovsky, 1950; Byers,
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1967) or in the transmission of virus and other pathogens for diseases, the symptoms of which 
include yellows, chiorotic streaks, necrosis of the phloem and tumor (Smith and Brierley, 
1956; Day and Venables, 1961; Kennedy et al, 1962; Watson and Plumb, 1972).
1.2.4 Insect pests of citronella
There is scanty information on insects associated with citronella because of the lack 
of systematic literature on both the crop (Gour et al, 1991) and insect pests (Sontakke et al, 
1991). Nevertheless, insects appear to be a problem to the root, stem and leaves of citronella 
(Sontakke et al, 1991, Gour et al, 1991). For instance, the worker termite Microtermes obesi 
(Isoptera; Termitidae) and the white grub, Holotrichia consanguinea (Blanchard) (Coleoptera: 
Melolonthidae), attack the root and eventually the stem leading to the death o f the plant 
(Sontakke et al, 1991). The same authors reported further that between 20 and 30% of the 
stems of young citronella are severely infested by the larvae of Chilo infuscatellus (Snellen) 
(Lepidoptera: Pyralidae), a stemborer. Gour et al (1991) identified the larva of 
Stemmatophora fuscibalis (Snellen) (Lepidoptera: Pyralidae) as a stemborer of citronella. In 
Ghana, the stem is attacked by the larvae of Eldana saccharina Walker (Lepidoptera: 
Pyralidae), Sesamia sp. (Lepidoptera: Noctuidae) and Atherigona sp. (Diptera: Muscidae) 
(Botchwey, personal communication).
The leaves are attacked by both the adult and the nymph of Anaphothrips sudanensis 
Trybom, Chloethrips holorphnus (Karney) (Thysanoptera: Thripidae), Macrosiphum 
miscanthi (Talcahashi) (Homoptera: Aphididae), the larvae of Mythimna separata (Walker) 
(Lepidoptera: Noctuidae) and the nymphs of Colemania phenarioides Bol (Orthoptera: 
Acrididae) (Sontakke et al, 1991). Infested leaves are characterised by white patches and sap
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sucking by the insects results in some leaves curling inwards longitudinally from the margin 
while others dry at the tip ( Sontakke et al, 1991).
Three species of leaf hoppers, Zygina manensis, Neophotettix nigropictus and 
Typhlocyba maculifrons (Homoptera: Cicadellidae) have also been found to be associated with 
the leaves of citronella, but the pest status and the nature of damage caused by these insects 
were not ascertained (Sontakke et al, 1991).
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CHAPTER TWO
2.0 INSECTS ASSOCIATED WITH CITRONELLA
2.1 Introduction
Grasses are generally visited by many insects, some of which are plant feeders, 
predators, parasitoids and casual visitors. For instance, Watts (1963) collected insects made 
up of 9 orders, 55 families, 109 genera and 120 species of the above categories on black grama 
grass. Other poaceous plants like maize, sorghum, millet, wheat, oats, barley, sugar cane and 
rice also interact with insects in various ways (Tams and Bowden 1953; Ingram 1958; Nye, 
1960a; Harris, 1962 and Deeming, 1971).
There is lack of information on the insects associated with citronella. Only few 
workers like Sontakke et al (1991) and Gour et al (1991) have provided some information on 
insects attacking the crop and from their work, the leaves, stems and roots of citronella are 
attacked by various insects in India (Section 1.2). However, information on insect abundance 
and activity on the crop can be obtained from surveying the insect complex through various 
sampling methods including light traps, Malaise traps and sweep nets (Southwood, 1968). 
Pre-proposal visits to citronella farms in the Greater Accra and Eastern Regions showed the 
presence of several insects on the crop with those of economic importance occurring in 
immature stages in the shoot. This study was therefore undertaken to find the occurrence of 
general insects, insect feeders (pests), potential feeders and the natural enemies of these 
feeders, where possible.
2.2 Materials and methods
2.2.1 Sampling points and climate
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The studies were carried out mostly on farms in the Greater Accra and Eastern 
Regions of Ghana (Fig. 1). In the Eastern Region, data were collected from farms at Omenako 
and Kpankpan-Ayikuma near Suhum. In the Greater Accra region, data were collected from 
Ashalaja, Ababio and Selina Taylor farms at Ayikuma in addition to data collected from a 
farm at Botoku, near Pokuase. Detailed studies were carried out at Osofoiaman in the Greater 
Accra region, where two farms were located. All the farms in the Eastern region were located 
in the forest zone. The rest were in the coastal savanna. *
Osofoiaman is a small village, about 15 km north-west of Accra (Fig. 1). It lies on 
latitude 5°44' N and longitude 0°.16' W. on the southern-most portion of the Akwapim 
ranges. The main occupation of the people is farming. Pineapples and citronella are the main 
cash crops which are cultivated, together with food crops like cassava, maize and vegetables. 
Farm A at Osofoiaman was located at about 200 meters south of the village. It was part of 
Kate citronella farms and it was located about 40 meters from an older and larger farm. Farm 
A measured about 88 x 18.5 m and it contained about 1800 citronella hills cultivated without 
any ploughing. It was bordered by wild grasses, maize and an abandoned farm of plantain and 
banana. The soil was mainly sandy loam and clay. The latter contributed to the flooding of 
the farm during rains since it was poorly drained. Farm B belonged to a small scale farmer. 
It was located about 300 meters N.W. of the village. The size was 58 x 42m with about 1570 
citronella hills, also cultivated without ploughing. It was bordered by pineapple and citronella 
farms, grasses, cassava and maize. The soil was sandy loam and well drained.
The climatic factors are summarized in Appendix I. Even though Osofoiaman lies 
within one of the driest zones in Ghana (The Accra plains), its climate is ameliorated by relief
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Fig 1: Map of Southern Ghana showing locations where sampling was done.
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rains from the Akwapim ranges. The climatic data presented in this section were obtained 
from the Ghana Meteorological Services, Legon, from their station at Pokuase, 4km west of 
Osofoiaman, for a five year period (1987 to 1991). Temperatures varied little from year to 
year. Average maximum temperatures for the period ranged between 29.3°C (in August) and 
34.7°C (in February). The average minimum temperatures ranged between 20.7°C (in 
January) and 23.6°C (in February).
The values for the relative humidities were calculated from the dry and wet bulb 
readings at 0900 hours and 1500 hours. Higher r.h. values recorded at 0900 hours ranged 
between 88 and 94%. Relative humidities at 1500 hours were lower; ranging between 70 and 
88%. The r.h. regimes exhibited an inverse relationship with those of the temperature. Thus 
the hottest period of the year had the lowest humidity with the reverse also being true for the 
coolest periods of the year.
There was a steady increase of the average evaporation rates from January (1.9 mm.) 
to April (2.6 mm.) and subsequently decreased over the months to December (1.6 mm.).
The lowest rainfall was 8.8 mm in January and the highest, 202.4 mm in May. The 
rainfall was bimodal with the first rainy season beginning in April and ending in July. The 
second one began in September even though August was not completely dry and it ended in 
November. .
The other sites showed similar climate and four distinct seasons were recognized as 
follows:
1. hot season from March to April and also from October to November,
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2. cool wet season from May to July and September,
3. cool dry season from August with little rainfall, and
4. hot dry season from December to February, which was the driest period with 
low rainfall and low humidity and very high temperatures and high evaporation. This 
is the harmattan period of cool nights and hot days and dry winds.
2.2.2 Sampling procedures 
2.2.2.1. Insects on Citronella Shoot (Leaves and Stems)
Insects whose interaction with the shoots of citronella were not obvious were sampled 
intensively and extensively using the sweep net, which is more appropriate for sampling 
insects on shoot of grasses because it samples about two thirds of the plant height (Nielson, 
1957). It is simple to use and provides rapid estimates of insect distribution, activity and 
abundance (Balogh, 1958). The intensive sampling involved the continual observation of the 
populations of insects that visited citronella at two areas and was carried out at Osofoiaman 
Farm A for six months (January to June, 1991.) and at Osofoiaman Farm B for 11 months 
(February to December, 1991) except in May when heavy rainfall made sweeping impossible.
Investigations on Farm A had to be discontinued in June when the field was 
completely destroyed by floods. The farms were visited weekly and sweeping done before
10.00 a.m. except when it was raining or when the visit coincided with the harvesting time of 
the farmer. Sweeping was done with a standard insect net of diameter 47 cm and depth 46 cm. 
Ten to and fro swings constituted one sample, which was transferred into a killing jar charged 
with ethyl acetate. Twenty samples, made up of five along each diagonal and each of two 
opposite sides of the farm were taken. The samples were ‘taken to the laboratory where the
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insects were identified, using keys and museum specimens, and their numbers recorded. Some 
of the insects were pinned, dried and kept in boxes while others were preserved in 70% 
alcohol.
The extensive sampling, was aimed at studies on the distribution of insects 
associated with citronella in the study area and was conducted in six farms at Osofoiaman 
(Farm C), Botoku, Omenako and Kpankpan Ayikuma near Suhum and Ayikuma near Dodowa 
(Selina Taylor and Ababio's farms). Each of these six farms was sampled with an improved 
net (Fig. 2b) at about three-week intervals, between the last week of October and the last week 
of December 1992. At each farm, 50 x 40 m was demarcated and sweeping done as in the 
intensive sampling. Insects collected were killed and identified as above. The extensive 
sampling had to be done between 11.00 a.m. and 3.00 p.m. because of problems from using 
public transport.
2.2.2.2 Insects (pests) damaging citronella
Insects damaging the leaves: Feeding on the foliage of citronella by insects may be 
manifested as defoliation of the plant, necrosis or curling of the leaf (Sontakke et al, 1991). 
Thus, this study was initiated in experimental Farm B to find the prevalence o f these 
symptoms and the insects responsible. Moving in a zig-zag fashion from one long side o f the 
farm to the other, every eighth (8th) plant was sampled and all the leaves inspected for 
defoliation, necrosis and curling. Such leaves were counted and recorded. Sampled plants 
were marked with pegs and skipped if encountered again. This was done monthly for six 
months, (February, March, June, September and November in 1991). It was repeated 
fortnightly, between the last week of October and last week of December, 1992 in Osofoiaman
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(Farm C), Botoku, Omenako, Kpankpan-Ayikuma, Selina Taylor and Ababio farms. The study 
was done on the same demarcated plots for sweeping as above. (See 2.2.2.1)
Insects damaging the stem: From preliminary studies at Osofoiaman, Ayikuma and 
Ashalaja, between November, 1990 and January, 1991, insect infestations were observed in 
the stems of citronella in all the farms visited. The following survey was thus initiated to 
find out the species of insects involved. The work was done at Osofoiaman Farms A and B, 
from January to June, 1991 and thereafter continued on Farm B and other farms at 
Osofoiaman, Botoku, Ayikuma and Ashalaja till December.
'Deadheart’ symptom, which is the gradual yellowing and browning of the innermost 
whorl of the tiller, as a result of damage by insects in the stem, was used to identify tillers 
infested by the shootborers. At Osofoiaman farms'A and B, randomly selected citronella hills 
were inspected weekly and all tillers counted. Those showing 'deadheart1 symptoms were 
removed, using a scapel and classified as either early deadheart1 tiller, advanced 
deadheart1 tiller or secondarily infested1 tiller in the case of Diptera. The inner whorl of a 
healthy tiller was pale green but infested tiller classified as early deadheart1; (i.e. freshly 
attacked) had the inner whorl just beginning to wilt and changing from pale green to greenish 
yellow. An 'advanced deadheart1, had the inner whorl wilted and the colour ranging from 
yellow to brown and may have multiple infestation by Diptera. The secondarily infested1 tiller 
was a condition where the tiller had already been attacked by a Lepidoptera before the Diptera. 
Those tillers that had been attacked by Lepidoptera only, were classified as 'Lepidoptera1. All 
the tillers showing ' deadheart' were taken to the laboratory and dissected, to determine the
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causes of the 'deadheart'. Tillers with dipterous larvae were carefully closed again and the 
portions with the larvae cut into 5-8 cm pieces, which were then stood in 10 x 2 cm tubes 
having moist cotton wool at the bottom, corked but opened frequently to allow in air (Plate2). 
The moist cotton wool prevented the cut tillers from drying quickly. The set up was inspected 
daily until adult flies emerged. If pupae of the Diptera were obtained from the tillers, they 
were placed individually in 10 x 2 cm tubes without moist cotton wool until adult flies 
emerged. Representative adults were labelled and sent to the British Museum for 
identification. Subsequently, all adults were identified using the keys provided by the British 
Museum. A key (Appendix 4), was eventually prepared for the shootflies identified in this 
study. The larvae of the Lepidoptera were either preserved or reared to adulthood and later 
identified. To preserve the larvae, they were killed in hot water of about 60°C, passed through 
40% and 60% alcohol and finally stored in 70% alcohol. The hot water ensured that the larvae 
maintained their colour patterns.
Farms at Ayikuma, Botoku and Ashalaja were also inspected monthly till December, 
1991, for 'deadheart' tillers and treated as those obtained from Osofoiaman Farms A and B. 
Insects damaging citronella root: Farms at Osofoiaman, Botoku, Ayikuma and Ashalaja 
were visited every two months between January and December, 1991, and citronella plants 
inspected for damage by root pests. Ten blocks of plots measuring 4 x 4 m were randomly 
selected and all the hills inspected. The presence of termitaria around the plants, and or the 
wilting of the leaves other than the inner whorl of the tiller, indicated the presence of root 
feeders, especially termites, in the roots. Such plants were uprooted and the underground parts 
examined. Termites were the only insects seen and some of them were collected for
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identification.
Natural enemies: Thirty- eight adults, 57 pupae and 172 larvae of the shootflies and 5 
lepidopterous stemborer larvae which died during rearing and 320 termite pests collected were 
kept in glass tubes sterilized by boiling and inspected for parasitoids and fungal growth. 
Predators were not screened but observations were made of insect activities in the field for 
predation.
2.2.2.3 Comparison of the Efficiencies of Improved and Standard Sweep Nets: It was 
observed from the intensive survey that the standard sweep net (Fig. 2a) caught rather low 
numbers of insects, especially smaller insects. The opening of the net was so wide that before 
the contents could be removed, swifter as well as and smaller insects would escape. An 
improved net was therefore designed and its efficiency compared with that of the standard 
sweep net. The improved net (Fig. 2b) had a narrower opening of diameter, D, 36.5 cm and 
a total depth, P, of 74 cm as against 52.5cm and 55.5cm, respectively, of the standard net. The 
nets were made of grey baft but the improved one had a detachable sac, T, of muslin material 
at the bottom of the net. After a collection has been made the detachable sac is closed by 
constricting the mouth with string, S. To determine their respective efficiencies, twenty 
samples were taken for each of the nets on a plot of citronella at Pokuase similar to what was 
done in the intensive sampling. The number of insects caught in one sample was counted, the 
time to make ten sweeps and get the insects into the killing bottle determined with stop watch, 
and insects caught per unit time, calculated for each net.
2.2.2.4 Comparison of Sampling Methods: Very low levels of infestation were recorded 
using 'deadheart’ symptoms alone to score infestation. In this experiment, therefore, results
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from this method were compared with those of another one to find out if  there was any 
difference. Based on the assumption that infested tillers that manifested in deadheart' 
symptom and those that did not, stood equal chance of being sampled, two methods for 
sampling shootborer infestation, viz, sampling using visual 'deadheart' symptom and sampling 
by random dissection were compared as follows; some 366 tillers were randomly removed 
and inspected for 'deadheart' symptom. Then they were all dissected carefully and inspected 
for shootborers. Percentage infestation as determined from the incidence of 'deadheart' was 
compared with that from random dissection, the null hypothesis being that there was no 
difference between the two. The comparison was replicated in 4 different farms.
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Plate 2: Rearing of insects from cut citronella shoots.
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L
a
Standard Sweep net
Improved Sweep net
7
The standard and Improved sweep nets
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2.3 Results
2.3.1 Insects on citronella shoot
Intensive sampling: A total of 1093 insects of 20 families, belonging to eight Orders; 
Hemiptera, Coleoptera, Hymenoptera, Diptera, Dermaptera, Orthoptera, and Dictyoptera were 
collected in the 11 months study period at Osofoiaman Farm B and were associated with the 
shoot of citronella (see Appendix 2). Homoptera was the most abundant followed by 
Hymenoptera and then Hemiptera. The populations of the families: Cercopidae (Homoptera) 
and Formicidae (Hymenoptera) were consistently high throughout the survey. ForSculidae 
(Dermaptera), Pyrgomorphidae (Orthoptera), Diopsidae (Diptera), Lagriidae and 
Chrysomelidae (Coleoptera) also occurred in most months of the year but in low numbers. 
Extensive sampling: A total of 4567 insects, belonging to 10 Orders and 102 families were 
recorded associated with the shoot citronella in the other six farms (see also Appendix 3). The 
breakdown is as follows; 751 insect belonging to 8 Orders and 52 families were recorded at 
Osofoiaman farm C, 951 insects (9 Orders and 49 families) from Botoku and 682 insets (10 
Orders and 49 families) from Abobio farms. The rest were 716 insects of 10 Orders and 47 
families from Selina Taylor farms, 649 (9 Orders and 53 families) and 907 insects (10 Orders 
and 55 families) from Omenako and Kpankpan-Ayikuma farms respectively. The spectrum 
of diversity of insect fauna in farms in the forest zone was similar to that in the savanna. Also 
the member of families representing an order was in no way an indication of the degree to 
which such groups contributed to the total insect population. For example, Homoptera had 
eight families yet contributed 1613 insects but Hymenoptera with 12 families and Coleoptera 
with 10 contributed 160 and 83 insects, respectively.
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2.3.2 Insects damaging citronella
Insects feeding on citronella leaves: The results (Table 1) showed that percentage necrosis 
in citronella leaves at the 7 different farms ranged between 0.0001% and 0.004%; that of 
curling was 0.001 and 0.008%. and defoliation between 0.0002% and 0.008%. This shows 
that negligible proportions of citronella leaves were attacked by insects.
Zonocerus variegatus
Zonocerus variegatus was the main species of Pyrgomorphidae (Orthoptera) collected in this 
study. It occurred in 8 months of the year in the intensive survey (Appendix 2) and in all 
farms in the extensive one, forming 73% of the Orthoptera group (Appendix 3). During the 
study, no feeding activity by the insect was observed in any of the farms visited. After the 
study period, however, it caused damage to citronella at a farm at Botoku near Pokuase. The 
damage was done by the adults and nymphs alike and large numbers of the species attacked 
the leaves at the edge of the blade and ate progressively towards the midrib which was left 
intact (plate 3).
Table 1: Foliar damage by insects to citronella leaves in different farms.
Farm Total number of Percentage leaves showing
leaves inspected Necrosis Curling Defoliation
(%) (%) (%)
Osofoiaman farm B 18,314 0.00047 0.00025 0.0003
Botoku 17,917 0.00049 0.00012 0.008
Osofoiaman farm C 15,564 0.0002 0.00089 0.0004
Omenako 13,709 0.0033 0.0013 0.0003
Kpankpan-Ayikuma 16,315 0.0041 0.0079 0.0009
Selina Taylor’s 31,794 0.00084 0.00047 0.0003
Ababio's 27,842 0.00011 0.000411 0.0002
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Insects in citronella stem: The results (Table 2) showed 8 identified and 2 unidentified 
species of Diptera and also 2 identified ones of Lepidoptera. The Lepidoptera was present 
only in freshly infested tillers while the Diptera occurred in fresh as well as already infested 
ones. From Chi-square analysis of the data (Appendix 5), the numbers of different insects 
reared from the different stages of ’deadheart’ were significantly different (X2 = 192.29; p <
0.05). The predominant insect therefore was Scoliophthalmus trapezoides (Fig. 4) followed 
by Anatrichus pygmaeus (Fig.8b), S. micantipennis (Fig. 5), species D, E, Sesamia sp., 
Aprometopis flavofacies (Fig. 7), Silba pectita, Elachiptera occipitalis (Fig. 8) and Eldana. 
saccharina.
Table 2: Adult Diptera reared, and Lepidoptera larvae collected, from tillers showing 
'deadheart1 symptoms from Osofoiaman and other farms in 1991.
Insects Total number of insects Number of insects from 'deadheart'
reared/ collected
'Early' 'Late' or 'advanced' ’2°'
Diptera: Chloropidae Scoliophthalmus 64 21 35 S
trapezoides Becker (48) (17) (26) (5)
Scoliophthalmus micantipennis Duda 45 39 6 0
(39) (35) (4) (0)
Anatrichus pygmaeus Loew 46 0 14 32
(17) (0) (6) (11)
Elachiptera occipitalis Becker 3 0 0 3
(2) (0) (0) (2)
Aprometopis flavofacies Becker 5 5 0 0
(5) (5) (0) (0)
D 32 0 8 24
(18) (0) (5) (13)
Diptera: Lonchaeidae Silba pectita 4 0 3 1
McAlpine (2) (0) (1) (1)
Diptera: Phoridae 15 0 10 5
E (7) (0) (5) (2)
Lepidoptera: Noctuidae Sesamia sp 11 11 0 0
(11) (11) (0) (0)
Lepidoptera: Pyralidae Eldana saccharina 2 2 0 0
Walker (2) (2) (0) (0)
( ) Number of 'deadheart1 tillers.
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Insects damaging citronella root
The results have been summarised in Table 4. Of the 12 farms visited, seven showed 
termite infestation; three severe, i.e. >10% and four mild i.p. <10%. Six of the infested farms 
were more than one year old, while one was less than one year old. The termites were not 
identified but their damage, which was caused by the workers, resulted in wilting and 
complete death. The hills were girdled with soil sheathing at, or just below, ground level. 
Examination of uprooted affected hills showed that the workers had eaten around the roots and 
into the stems, and had them filled with soil.
Table 3: Incidence of termites in sampled farms, in Greater Accra Region, 1991.
Location Farm Age of Plants Total No. of hills inspected Percentage
> lyr. < I yr. infestation
(%)
Ayikuma Tagoe farms II 1972 37.2
Vas farms I II 1916 0
.. „  j j l< 2304 4.0
Ashalaja New Match II 1920 . 14.0
farms I
New Match II 1692 4.3
farms II
Botoku Farm I II 1713 0
“ II II 1841 0
" III II 2024 3.1
Osofoiaman Kate farms I II 1724 0
* " II II 2074 23.0
Experimenta II 1676 0
1 farm B I
Experimenta II 1978 0.7
1 farm B II
Natural enemies: No parasitoids were observed form the dead insects, neither were there 
any pathogenic fungi. Also no predatory activity was observed in the field.
2.3.3. Comparison of Efficiencies of the Improved and Standard Sweep Nets: The results
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are summarised and analysed in Table 4 below. There were significant differences in insects 
caught in 20 samples at 10 sweeps per sample (t = 4.14; P < 0.05), in time to handle one 
sample (t = 4.54; P < 0.05), and in the rate of catch between the improved and standard nets 
(t = 6.30; P < 0.05). The former caught more insects and also it was quicker to handle its catch 
than the latter.
Table 4: Analysis of twenty (20) samples of insects each by Improved and Standard
Sweep nets at 10 sweeps )er sample.
Type of Range Mean 3̂Sd f. (0 05)
Sweep net x ± S.E.
Time for 1 sample Improved 58.0-75.3 65.62±.99 *4.54
(seconds)
Standard 77.0-164.0 100.18±7.55
Number of insects Improved 10-45 23 .O il.9 *4.14
caught
Standard 3 - 31 12.3±1.7
Rate Improved 0.133-0.703 0.353±.029 *6.30
(Catch per second)
Standard 0.034-0.295 0.133±.029
* Significant at p < 0.05.
2.3.4 Comparison of Sampling Methods: The results are summarized in Appendix 6 and 
further illustrated in figure 3. The percentage infestation estimated from 'deadheart' symptoms 
alone underestimated the real infestation level which is determined from random dissection. 
The difference between the two methods was higher at Osofoiaman and Ashalaja than the 
remaining 2 farms.
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□  Only deadheart symptom 
El Random dissection
Omenako Ababios
Farm
Fig.3 Infestation rates as determined by only "deadheart" symptom and by random 
dissection
Percentage infestation
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Fig 4: Dorso-lateral view of female Scoliophthalmus trapezoides
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X 35
Fig. 5: Dorso-lateral view of female Scoliophthalmus micantipennis
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Fig. 7: Dorso-lateral view of female Aprometopis flavofacies
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X 4 0
Fig 8: Lateral view of female Elachiptera occipitalis
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Plate 3: Zonocerus variegatus attacking citronella on the farm.
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2.4 Discussion
Insects on citronella shoot
The relative abundance of insects with respect to months might not be reliable in the 
intensive survey because of the inconsistency in the number of collections made per month; 
For instance, no collection was made in May, 1991 because sampling coincided either with 
rain or harvesting. Nevertheless, the results show that the vegetative growth of citronella 
supported a remarkably rich and diverse insect fauna. Thus from both intensive and extensive 
surveys, a total of 5660 insects belonging to 10 Orders and 103 families were found associated 
with the shoot of citronella and fairly distributed over the study area. The insects are mainly 
grass feeders, their parasitoids and predators.
The grass feeders include Cercopidae, Cicadellidae and Aphididae (Homoptera) whose 
feeding activities result in viral transmission (Watson and Plumb, 1972; Borror et al, 1976). 
Included also are Coccinellidae (Coleoptera) which attack leaves of maize and rice in Ghana 
(Schumutterer, 1969; cited by Scheibelreiter and Inyang, 19-74); Pyrgomorphidae (Orthoptera), 
Chloropidae and Lonchaeidae (Diptera) some species or which have been found to interact 
with citronella in this present study. Most of the grass feeders appear innocuous presently but 
they may subsequently assume important status as citronella cultivation continues. They are 
therefore a potential threat.
The predators include Chaemaeyiidae (Diptera), Sphecidae (Hymenoptera) and 
Mantidae (Opthoptera). Several members of Chaemaeyiidae and Sphecidae prey upon the 
grass feeders Aphididae, Cicadellidae and Delphacidae (Homoptera) (Watts, 1963; Thomas, 
1968, Evans, 1968) which are found in large numbers on citronella. Significantly the
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species of Mantidae were green in colour or a combination of that colour to offer them good 
camouflage within the citronella leaves for their predatory activities. Among the parasitoids 
are Diapriidae, Braconidae, Eulophidae and Ichneumonidae (Hymenoptera), some species of 
which have been found by Simmonds (1952) to parasitise on other chloropids such as 
Oscinella frit. These parasitoid families are therefore important because they could be 
investigated for use in the biological control of the Chloropidae that damage citronella.
Insects damaging the leaves
Though the results showed large number of grass feeding families like Cercopidae, 
Cicadellidae, Psyllidae, Delphacidae, Aphididae (Homoptera), Pentatomidae, Lygaeidae, 
Tingidae (Heteroptera), Corimelaenidae, Curculionidae, Cerambycidae, Lagriidae, Meloidae, 
Elateridae, Pselapidae (Coleoptera) and Pyrgomorphidae, Tettigonidae (Orthoptera), none of 
their adults was observed feeding on the leaves of citronella during the survey. Results from 
further investigation also showed negligible symptoms of feeding activities by insect foliage 
pests. For example, less than 0.005%, 0.002% and 0.009%, showed necrosis, curling and 
defoliation respectively, resulting from insect attack. The present findings are similar to those 
made by Sontakke et al (1991) who, however, failed to indicate the extent of the damage. The 
absence of major foliage insect pests might be due to the repellent properties of the essential 
oils present in the leaves (Saraswathi and Rao, 1987; Bosch, 1971).
However, Zonocerus variegatus L. (Orthoptera: Pyrgomorphidae) is a potential 
foliage pest of citronella because of the isolated case of the species feeding extensively on the 
leaves at Botoku in 1992 (Plate 3) after the study period. Even though the insect ate any 
vegetation available and not only citronella it still poses a threat because of the extent o f its
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damage and its strong presence in citronella farms.
Insects damaging citronella stem
The results showed that the major insects that damaged citronella were found in the 
stem. The dipterous shootflies (Chloropidae), are particularly dominant. The presence of 
Chloropidae in citronella in this study shows their affinity for poaceous plants and wide 
distribution, especially in Africa. This is because species of the family, including 
Scoliophthalmus trapezoides, Scoliophthalmus micantipennis, Anatrichus pygmaeus and 
Aprometopis flavofacies have also been reported (Deeming, 1971; Le Pelley,1959) as attacking 
sorghum, maize, millet, guinea com and wild grasses in Nigeria, Kenya, Tanzania, Uganda, 
Cameroun, Zimbabwe, Senegal and Nigeria.
The results also suggest that the shootborers occupy at least three different feeding 
niches in citronella, primary feeding, secondary feeding and scavenging. Follow up 
experiments to determine the specific species occupying the different niches were unsuccessful 
because the insects failed to oviposit in captivity. However, species that damage fresh tillers 
are considered primary feeders if there is no evidence of the presence of other species, whereas 
those damaging previously infested tillers are secondary feeders and those found in tillers 
already attacked by Lepidoptera, apart from possibly being secondary feeders, might be 
scavengers or saprovores, or parasitoids or predators (Deeming, 1971).
In line with Demming’s (1971) classification therefore, A. flavofacies, Sesamia sp. 
and E. saccharina recorded in the present study, may be considered primary feeders of 
citronella, since they attacked only fresh tillers. The conclusions on Sesamia sp and E.
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saccharina agree with observations elswhere (Tams and Bowden, 1953; Ingram, 1958; Nye, 
1960a and Harris, 1962). S. micantipennis is also considered primarily as a primary feeder 
because as high as 86.7% of them attacked fresh tillers. The conclusions on the status o f S. 
micantipennis and A. flavofacies agree with those made by Deeming (1971) who, working in 
Samaru in Nigeria, concluded that these insects cause primary damage to sorghum and millet 
tillers, respectively.
Scoliophthalmus trapezoides was considered both a primary feeder and a secondary 
feeder since it damaged both fresh (32.8%) and already infested tillers (54.7%). The status of
S. trapezoides as a secondary feeder, agrees with the conclusion made by Deeming (1971), 
who found the insect causing secondary damage to sorghum and maize tillers. The status of 
A. pygmaeus, S. pectita, E. occipitalis and chloropid sp. D, was not clear since they were 
frequently found in both tillers already infested by other Diptera and Lepidoptera. However, 
the larvae of A. pygmaeus have been reported by Sabrosky (1962), cited by Deeming (1971), 
as being predaceous on other larvae.
The role of the Phoridae reared from citronella could also not be determined, but some 
species of the family have been recorded (Ingram, 1958) as being parasitoids of the 
Lepidoptera, Busseola fusca (Fuller) (Lepidoptera: Noctuidae). In this study, they were 
probably attracted by the presence of the Lepidoptera, E. saccharina or Sesamia sp in the 
citronella tillers.
The primary feeders are the most important insects since they initiate the attack on the 
plants (Deeming, 1971). Of the primary feeders observed in the present study, S. 
micantipennis constituted about half the number and it, is therefore considered the most
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important feeder of citronella. This observation agrees with a conclusion made by Deeming 
(1971) that S. micantipennis is one of the most important primary feeders of sorghum.
Insects damaging citronella root
Results from the study showed that only unidentified species of termites belonging to 
the family Termitidae (Isopterea) cause damage to the roots of citronella This observation is 
in line with that made by Sontakke et al (1991) in India. .The damage observed was not as 
widespread as that by the shootborers, as the termites were found in only 58.3% of the farms 
visited whilst the shootborers were present in all the farms. Despite their limited distribution, 
the termites pose a great threat to the citronella industry because their damage could result in 
the destruction of a whole hill, leading to herbage loss and reduction in oil yield.
The incidence of termites in citronella farms is probably related to the history of 
cultivation. In particular, long term cultivated farms have higher incidence than short term 
ones. For this reason 85.7% of infested farms had more than one year of cultivation as against 
only 16.7% which had less than one year. This observation agrees with the one by Wood et 
al (1977) who found long term cultivated soils to have higher population densities of termites 
than soils in the first year of cultivation. The reason found for this is that as the farms are 
cultivated, the availability of roots of natural vegetation decreases in the soil with the duration 
of cultivation (Black and Wood, 1989). The termites are therefore forced to forage more 
intensively on the surface (Wood et al 1980)
The exact relationship between age of citronella farm and severity of termite damage 
could not be established, because the exact ages of the farms could not be determined. It is 
however, suggested that the area be further investigated, since it could help determine how
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long citronella farm could be kept in the savanna without attracting too many termites.
Natural enemies
The insects collected from the shoot included predator and parasitoid families but no 
parasitoids were found in the field or from laboratory screening. This is in sharp contrast to 
the results by Simmonds (1952), in which numerous hymenopteran parasitoids from 
Chalcidae, Pteromalidae, Diapriidae, Prototrupidae and Cynipidae were found associated with 
Oscinella frit (Diptera, Chloropidae). Predators were not screened for, however, the absence 
of parasitoids and pathogenic fungi is probably because the shootborer populations were very 
low, as depicted by the low infestations (Fig. 13) and that not many insects could be screened.
Comparison of Sweep Nets: Results of the comparison of the sweep nets showed 
that the standard sweep net is less efficient for assessing insect population as observed by 
Strickland (1961) also. Thus the standard net caught about a third (0.13 + 0.02) of the insects 
caught by the improved one (0.35 + 0.02). Also it took longer time to collect a sample using 
the standard net (100 ± 7.6s) than using the improved one (65.6 ± 0.1s). Furthermore, the 
improved net caught the smaller insects more than the standard one. For example as many as 
25 small adult chloropid shoot flies whose larvae damage citronella tillers were caught with 
the improved net as against none by the standard net at Osofoiaman Farm B. The improved 
net should therefore be developed further for use in sampling insects on the Poaceae.
Comparison of Sampling Methods: T-test analysis, after square root transformation 
of the data showed that the percentage infestation determined from only 'deadheart' symptom 
(mean, 0.77%) was significantly lower than that determined from random dissection (mean, 
1.13%) (t = 3.18; P < 0.05). The null hypothesis is therefore rejected. Indeed there is a
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function of y = 1.078x + 0.3 between the two rates where y = percentage infestation by 
dissection and x that by only 'deadheart'. Thus, shootborer infestation determined from only 
visual 'deadheart' symptom underestimate the actual infestation by (1.078x + 0.3) -  x, about 
31.8% on the average, probably because freshly attacked tillers without 'deadheart’ symptoms 
were missed. The results are by no means conclusive, considering the small number of 
replicates, i.e. 4, and also the fact that it was not possible to repeat the work in the replicates. 
Therefore, there is the need to investigate further to establish a very reliable relationship 
between the two methods for predictive purposes.
In conclusion, the major insects damaging citronella were found to be dipterous 
shootflies and lepidopterous stemborers. The minor ones were termites which attacked the 
root and the stem. No natural enemies were found. The dipterous shootflies belonged mainly 
to Chloropidae. Zonocerus variegatus is a potential pest of the leaves even though the leaves 
are not seriously damaged by insects. The major feeders are more important, hence a further 
look is taken of their damage in the next chapter.
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CHAPTER THREE
3.0 INSECT PREFERENCES FOR DIFFERENT
SIZES OF HOST PLANT AND 
NATURE OF SHOOTBORER DAMAGE
3.1 Introduction
In the previous chapter, the most significant insects causing damage to citronella were 
found to be lepidopterous stemborers and dipterous shootflies which bored into the stem. 
Earlier investigations found that the major pests of citronella were those that bored into the 
stem and led to an externally visible symptom known as the 'deadheart' symptom. The damage 
may be severe as in the case of Chilo infuscatellus Snellen (Lepidoptera: Pyralidae) (Sontakke 
et al, 1991) or mild as in the case of Stemmatophora fuscibasilis Snellen (Lepidoptera: 
Pyralidae) (Gour et al, 1991). Severe borer infestation may result in serious losses in crop and 
revenue, as occurred with Eldana saccharina Walker (Lepidoptera: Pyralidae), Sesamia sp. 
(Lepidoptera: Noctuidae) and Atherigona sp. (Diptera: Muscidae) (Botchwey, personal 
communication).
Infestation by a particular insect may be influenced by several factors including size 
and age of the host plant. Thus, bigger and taller hosts are preferred by lepidopterous stem 
borers (Patch, 1929; Chiang et al, 1960; Walker, 1963) while shootflies prefer smaller as well 
as shorter tillers (Deeming, 1971; Simmonds, 1952). In pre-proposal studies conducted at 
Mayera, Ashalaja and Ayikuma, smaller and shorter tillers appeared to be preferred by the 
chloropid shootflies. In this work, therefore, field studies were carried out to investigate insect 
preferences for different sizes of host plants. This could hfelp in the selection of materials for 
planting. A laboratory investigation of the boring of the insects was also carried out where
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possible to study the nature of damage done to the tiller.
3.2 Materials and methods
3.2.1 Field investigation of preference for size of citronella tillers by shootborers.
This preliminary investigation was conducted in the field to find out if the insects 
exhibited any preference in their choice of citronella tillers for attack.
A total of 70 tillers in two groups of 35 tillers each, already infested by each group of 
shootborers were randomly removed from farms at Omenako, Ashalaja and Ayikuma from 
October to December 1992. Measurements were taken of the tiller heights, diameters and 
lengths of tunnels in the laboratory. The lengths and heights were measured with straight- 
edged ruler while the diameters were measured with a micrometer screw guage. Measurement 
of the diameters were taken from two opposite sides of the base of the sheath in the region of 
the apex immediately above the uppermost exposed node. The results were analysed 
statistically, following the procedure by Walker (1963) and Endrody-Younga (1968).
3.2.2. Boring activity of the shootborers
In the previous chapter, adult shootborers were reared from infested tillers collected 
from the field. This experiment was therefore designed to find out how the insects bored into 
the tiller, their activity inside it and the effects of their activity on the tiller. Different larval 
instars of the shootborers were collected from field infested tillers and put on leaves and 
sheaths of potted citronella in the laboratory (Plate 4). They were inspected daily and boring 
activities such as point of entry into stem, direction of boring and effect on leaves were 
studied. After a larva had bored into a tiller and the inner whorl began to wilt, the tiller was 
dissected and the active larva transferred onto another tiller. In this way 13 lepidopterous
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larvae were made to bore into 35 tillers. Shootfly larvae obtained either died or pupated 
without attacking the plant.
3.2.3. Field identification of damage from differential growth (height) of newly ratooned 
infested and uninfested tillers
In the field, damage by shotborers has been most easily identified by only one index
i.e. 'deadheart’. This limits the ability of the farmer to detect early infestation in situations 
where 'deardheart’ symptom may not be showing particularly in freshly ratooned crop. This 
study was therefore undertaken to detect early infested crop without 'Deadheart’ symptom. 
A farm measuring 50 m by 40 m and lying adjacent to Farm B at Osofoiaman, was harvested 
five months after planting. Every fifth hill was selected along two opposite sides of the farm 
and also along the two diagonals. Five tillers were randomly selected from each hill and 
labelled. Thus a total of 60 hills and 300 tillers were sampled. The heights of the labelled 
tillers were measured with straight-edged ruler every morning for seven consecutive days until 
the infested tillers began to show 'deadheart1 symptom. The average growth of the infested 
tillers was compared with that of the healthy tillers.
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Plate 4: Experiment to study the boring activity of shootfly larvae.
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3.3 Results
3.3.1 Field investigation of preference for size of citronella tillers by shootborers
The results have been summarised and analysed in Table 5. The mean tiller heights 
of infested tillers by the shootborers were very close; so were the mean diameters. The range 
of heights of tillers infested were also similar. They ranged from short to tall tillers. Thus the 
shootflies attacked tillers ranging from 255 mm to 413 mm while the lepdopterous stemborers 
attacked those from 278 mm to 413 mm. Testing at 5% level of significance there was no 
difference between the means. Therefore the larvae of lepidopterous stemborers attacked 
citronella tillers that were similar in height and diameter to those attacked by the shooflies.
3.3.2 Boring activity of the shootborers
Lepidopterous stemborers: In the laboratory, boring was done by larvae of Sesamia 
sp and E saccharina. Both entered or left the tiller through entry/exit holes at a mean height 
of 21.0 + 14.7mm (Table 5) above the apex of the rhizome at the base of the tiller. On 
entering the tiller, a larva tunnelled vertically upwards and7or downward producing a lot of 
frass and creating a cavity at the apex of the rhizome (Fig. 9). Tunnels measured from field 
sampled tillers had mean length of 75.4 ± 23.6mm (Table 5). Tunnelling destroyed the apical 
region of the rhizome; it also caused the inner whorl to wilt to produce the 'deadheart’ 
symptom.
Shootflies: No boring was done in the laboratory. Therefore, the point of initial attack could 
not be determined. However, from field observations, the larvae tunnelled 32.7 ± 23.6mm; 
(Table 5) or ate the tissue of the inner whorl which became rotten to produce the 'deadheart’ 
symptom. The rotten material normally extended along the inner whorl to the apex of the
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rhizome which became destroyed. The attack also resulted in constrictions within the inner 
whorl (Fig. 10). If the constriction was pushed out of the tiller on top of a healthy growing 
inner whorl, the plant overcame the attack of the larva.
Table 5: Summary and analysis of tillers preferred and damaged by the shootborers.
Mean Tiller height Mean Tunnel Mean height o f  Mean Diameter o f  
(mm) length (mm) x ± entry/exit hole (mm) infested Tillers (mm) 
x ± s.d. s.d. ’ x ± s .d . x ± s.d.
Lepidoptera 355.3±37.7 75.4±23.6 21.0±14.7 10.3±2.5
Diptera 324.5±36.9 32.7±23.6 - 10.2±2.7
'34df (0.05) N.S. *6.55 N.S.
* Significant at p < 0.05
3.3.3 Field identification of damage from differential growth (height) of newly ratooned 
infested and uninfested tillers.
Three hills, i.e. numbers 13, 17 and 30, had both infested and healthy tillers present 
and both types of tillers increased in height with time (Fig. 11; Appendix 7). The curves 
coincided closely showing that the height of the infested and uninfested tillers had similar 
growth. Nevertheless, a slight deflection of the curves oflhe infested tiller numbers 13 and 
17 after the fifth day showed that they had a slight delay in growth.
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Fig. 9: Longitudinal section of tiller attacked by lepidopterous stemborer.
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Fig 10
Longitudinal section „ f  (iller a „ acked by s h o o (%
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Day
Fig. 11: Daily growth of healthy and infested tillers of ratooned citronella at 
Osofoiaman in one week in 1991.
Height of tillers of hill 30 (mm) Height of tillers of hill 17 (mm) Height of tillers of hill 13 (m m )
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3.4 Discussion
Field investigation of preference for size of citronella tillers by shootborers.
The results showed that the incidence of shoot flies and lepidoterous stemborers do not 
depend on tiller diameter and/or height. This is in contrast with the suggestion by Patch 
(1929) and Chiang et al (I960), that lepidopterous stemborers prefer taller hosts, as well as the 
observations by Simmonds (1952) and Deeming (1971) that shoot flies prefer smaller, shorter 
tillers for infestation.
Infestation by a mixture of stemborer populations of Busseola and Sesamia and also 
a purely Busseola population depend on the size of the hosts but that by a purely Sesamia 
population shows no preference for size (Walker, 1963; Endrody - Younga, 1968). It is 
therefore in consonance with the above findings that as observed in this study, a stemborer 
population almost entirely of Sesamia (Table 2) shows no preference for size. The results also 
confirm that the stemborer population in citTonella in South-Eastern Ghana consists mainly 
of Sesamia as indicated in Table 2.
However, the results are preliminary and further investigations ought to be carried out, 
especially at different ages of the plant for definite conclusions to be drawn.
Damage of the shootborers .
Correlation analysis showed that for the two shootborers the length of the tunnel did 
not depend on the height of the tiller. However, t-test analysis on field data (Table 5) showed 
that the length of the tunnel by lepidopterous stemborers (75.4±23.6mm) was significantly 
longer than that by the shootflies (32.7±23.6mm) (t = 6.55; P<0.05). Indeed, tunnels by the 
shootflies were less than half the length of those made by the lepidopterous
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stemborers. This may probably be due to the bigger size and more powerful mouth parts of the 
lepidopterous larva. Sesamia sp and E. saccharina entered straight into the stem through the 
sheaths, and this is in conformity with the observation made by Ingram (1958) and Harris 
(1962), who reported that the young Lepidoptera larvae, especially of Sesamia sp, bore straight 
into the stems of cereal crops.
The point of entry of the shootflies could not be determined either in the field or 
laboratory because of high mortality in the larvae but according to Simmonds (1952), in 
wheat, larvae of other Chloropidae e.g. Oscinella frit bore into any part o f the stem or 
between the tissue layers of leaves and descend to the lower part of the shoot.
The entry/exit points of the lepidoptera larvae were lower down the tiller close to the 
apical region of the rhizome. This observation agrees with that by Girling (1972), who 
reported that the larvae of E. saccharina bore into the lower part of the sugar-cane plant. The 
apex of the citronella rhizome is very soft and this might have served as a good source of food 
for the larva. It was also observed that the larvae frequently rested in the cavities they made 
in the rhizome. At that low position in the rhizome, they could easily be missed during 
harvesting, making it possible for them to re-infest the ratoon crop, which therefore suggests 
this might be an adaptive behaviour.
Damage by the larvae of the shootborers caused 'deadheart' symptom which results 
from the mechanical damage to the scattered vascular bundles during the boring activity (Nye 
1960a.). In addition to this, observations in the present study suggest that the deadheart' 
could also have been caused by the eating of the meristematic tissue at the apex of the rhizome 
by the larvae and also from the rotting of that point. The production of 'deadheart1 symptom
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by the Chloropidae has also been abserved by Deeming (1971) on other cultivated cereals and 
wild grasses. Nonetheless, there may be other symptoms from Chloropidae damage. For 
example, Goodlife (1942) found them to produce swollen nodes and intemodes referred to as 
gouted shoots while Simmonds (1952) reported the wilting of shoots of cereals from their 
damage.
Whereas the ftass and entry/exit holes are very characteristic of the lepidopterous 
stemborer attack, attack by larvae of the shootflies could be differentiated by the rotting and/or 
constrictions in the inner whorl. Agents causing the rotting were not determined but the 
destruction of the innermost part of the tiller agrees with Deeming’s (1971) observation on
S. trapezoides and S. micantipennis in sorghum and millet tillers. It also agrees with the 
report by Simmonds (1952) that O. frit destroyed the central part of the wheat stem.
Field identification of damage from differential growth (height) of newly 
ratooned infested and uninfested tillers.
Dissection of infested tillers showed the destruction of the apical meristem of the stem. It 
follows then that growth in infested tillers as expressed in their heights will slow down even 
if it does not cease completely. Therefore, assuming that harvesting affected both infested and 
healthy tillers equally; that tagging did not affect the physiological state of the plant; and that 
all healthy tillers in a citronella hill grow almost at the same rate, the differences in height 
would indicate infested and healthy tillers. The result in this study only showed slight 
differences in growth of infested and uninfested tillers after harvesting, i.e. after six days (Fig. 
11). The differences were too small to be recognised visually without measuring. Therefore 
they can not be used to detect early infestation which is not showing “deadheart”.
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CHAPTER FOUR 
4.0 SEASONAL VARIATION IN INFESTATION OF CITRONELLA  
BY LEPIDOPTEROUS STEMBORERS AND 
CHLOROPID SHOOTFLIES 
4.1 Introduction
Infestation of crops by insect pests tend to fluctuate in response to several factors both 
biotic and abiotic (see section 1.2). However, weather and climate are commonly accepted 
as dominant influences on the behaviour, abundance and distribution of insects. Thus, Reddy 
(1982) found the distribution of shootborer species to be influenced by rainfall, while the 
fluctuations in the incidence of pests with rainfall pattern has been reported by Adeyemi 
(1969), Harris (1962), Smithers (1960) and Easwaramoorthy and Jayaraj (1988). Temperature 
also has an effect on the dynamics of insect numbers (Balraj et al, 1977; Reddy, 1982); so 
also is relative humidity (Girling, 1978; Easwaramoorthy and Jayaraj, 1988). Climatic factors 
may also induce diapause in shootborers (Barry, 1972; Clearwater and Otieno, 1977; Ogwaro, 
1979).
There is lack of information on the effect of climatic factors on shootborer Infestation 
of citronella but such information is required for use in control planning. Therefore these 
studies on the progress of infestations in relation to rainfall, evaporation, temperature and 
relative humidity were carried out with this objective in mind.
4.2 Materials and methods
4.2.1 Determination of sample size and measurement of incidence of deadheart’ caused 
by shootborers
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Sample size: Two citronella farms at Osofoiaman were used in this study. Farm A measured 
88m x 18.5m and Farm B, 58m x 42m. All the citronella hills in the farms were pegged and 
numbered. The tiller was the sampling unit and preliminary studies were carried out to 
determine the sampling size, following the procedure by Hansen et al, (1962).
ie. K2 NV2
n = -----------
ND2 + K2 V2
where n = sampling size,
N = total number of tillers on farm,
V = ratio of failure to success in finding infestation in the tiller,
K = the probability that the sample result will have no error greater than + D, 
and D = allowable error.
Incidence of “deadheart”: The incidence of 'deadheart' by the shootborers was measured 
for both farms A and B. The work started in January 1991 and February 1991 in farms A and 
B, respectively. Farm A was monitored until June when it was abandoned because the farm 
became flooded and most of the citronella hills got destroyed.
From the procedure above, sampling size of between 1100 and 1200 tillers (see 4.3.1) 
were randomly selected from a box of numbers for a farm. Each farm was visited weekly. For 
any citronella hill sampled, the leaves were carefully inspected for eggs, larvae and adults as 
well as external damage symptoms. The tillers were counted and those showing 'deadheart'
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symptoms were recorded, removed with a scapel and dissected in the laboratory to determine 
the cause of the 'deadheart' symptom. Percentage infestations by the respective shootborers 
were then calculated.
4.2.2. Rainfall, Temperature, R.H. and Evaporation
Figures for rainfall, evaporation and temperature including wet and dry bulb readings 
were obtained from the meteorological substation at Pokuase. Mean relative humidity values 
were calculated from wet and dry bulb readings at 0900 Hours and 1500 Hours GMT. A 
stepwise regression analysis was done between infestation and climatic factors after square 
root transformation of percentage infestation.
4.3 Results
4.3.1 Determination of sample size and measurement of incidence of'deadheart' caused 
by shootborers.
Sample size: The total number of tillers and the infestation levels in both farms were
similar from the studies, so results from one farm were used to determine the sample size for
the two, as follows:
Total number of hills on farm =1530
Mean hill size = 34.6 tillers
Total number (N) of tillers on farm = 53000 
Number of tillers sampled = 1478
Number of tillers infested = 135
V = (1478 - 135~>
135 
= 9.95 
K = 1
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D = 0.3 (ie 70% confidence level)
n _ K2 Nv2 
ND2 + K2 V2
By substitution,
n = 53000 x 98.964
53000 x .09 + 98.964
simple size = 1077 tillers 
Incidence of “deadheart”: The results for incidence of'deadheart’ by shootborers in Farm 
B have been illustrated in Fig. 12 (see also appendix 9); those of Farm A in Fig. 13 (see also 
Appendix 8). In Farm B, where sampling spanned the period February to December 1991, 
percentage infestation by lepidopterous stemborers showed two possible peaks: a questionable 
peak around February and a distinct peak in October. That by the shootflies showed similar 
trend in the same months. Combined infestation was similar to that by the shootflies because 
the infestation by the shootflies was generally higher. In Farm A, where sampling spanned 
the period January to June 1991, the infestation levels for the lepidopterous stemborers peaked 
in February and dropped thereafter. That for the shootflies peaked in March and dropped to 
a low in May. However, it was beginning to rise in June when work was abandoned because 
of the excessive flooding of the field. Combined infestation also followed the trend by the 
shootflies. By comparing data from farms A and B, it appears there are two peaks in 
infestation. Analysis of variance following square root transformation of the mean 
percentage infestations showed no significant difference between infestation by the shootflies 
and stemborers (P > 0.05). Nevertheless, damage in Farm A by both groups of insects during
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the same period was higher than in Farm B. For instance, from February to June, the mean 
percentage incidence of'deadheart' by shootflies in Farm A was 0.65% and that of Farm B 
was 0.44%. Similarly, that by stemborers in A was 0.29% compared to 0.19% in Farm B. 
Generally, infestations were low in both farms (Figs. 12 and 13).
4.3.2 Rainfall, Temperature, R.H and Evaporation
The following results have been illustrated in Fig. 14 (see also Appendix 10). Rains 
started late in February at Osofoiaman and the wettest month was May. February and 
December were the driest months. Temperature did not vary much within the months. Mean 
monthly temperatures ranged between 25.5°C in August and 29.1°C in February and March.
The r.h. too did not vary much within the year; the lowest was 80% and the highest 91.5%. 
Mean evaporation had two peaks, 2.3 mm in March and 1.9 mm in December. There were 
weak linear relationships between 'deadheart' by both groups of shootborers and rainfall, and 
between deadheart’ caused by shootflies and other climatic factors of evaporation, 
temperature and relative humidity. A regression analysis of percentage deadheart' by 
lepidopterous stemborers and rainfall gave a relationship of y = -0.0017x + 0.6298 (Fig 15: 
Appendix 11). The relationship of shootflies and the climatic factors were as follows: rainfall, 
y = -0.0024x + 1.3413 (Fig. 16: Appendix 12); evaporation, y = -0.8958x + 2.2639 (Fig. 17: 
Appendix 13); temperature, y = -0.5826x + 17.15 (Fig. 18: Appendix 14); and relative 
humidity, y = 0.1292x -9.8968 (Fig. 19: appendix 15); where y = percentage 'deadheart' and 
x = climatic factor.
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fig. 12: Percentage 'deadheart’ caused by shootflies and lepidopterous stemborers, 
Osofoiaman farm B, 1991.
P»rt«nt*a* * d«ftd h t«n
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ten Fob Vivch Apal U«v JUf«
Month
Percentage 'deadheart9 caused by shootflies and lepidopterous stemborers, 
Osofoiaman farm A, January - June, 1991.
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Fig. 14: Mean montly rainfall ̂ evaporation, temperature, relative humidity and percentage 'deadheart’ 
by shootflies and stemborers, Osofoiaman farm B, 1991.
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Fig. 15 Relationship between percentage 'deadheart’ by stemborers and rainfall.
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Fig 16 Relationship between percentage deadheart’ by shootllies and rainfall.
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Evaporates ( raa]
Fig 17: Relationship between percentage deadheart’ by shootflies and evaporation.
Parcantaga ~ daadhaart  ~ by dlptaroui ■haotijo ran
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Tmnvmrtmrm ( C ]
Fig 18: Relationship between percentage deadheart’ by shootflies and temperature.
ius shQotfcaran
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&er
R«Urilv« honddy (X)
Fig. 19: Relationship between percentage 'deadheart’ by shootflies and relative 
humidity.
Pareantaga 'd a a d h a a r l' by dlptaraui m o o t to ra n
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4.4 Discussion
Incidence of deadheart' by shootflies and lepidopterous stemborers
Results of borer incidence in Farm A were not complete and therefore may not give 
much information but the fact that work had to be abandoned as a result of flooding, shows 
the unsuitability of marshy areas for the cultivation of citronella.
In Farm B, the results showed no significant difference (P > 0.05) between the means 
of infestation rates by the shootflies (1.2%) and stemborers (0.6%). Therefore, as far as insect 
attack of the plant is concerned, both groups of insects are equally important, even though 
percentage infestation by the shootflies was observed to be higher.
That infestation by the stemborers has two very distinct peaks is similar to the 
observation made by Endrody - Younga (1968) of infestation by E. saccharina and Sesamia 
botanephaga Tams and Bowden (Lepidoptera: Noctuidae). However, while Endrody -  
Younga’s (1968) peaks occurred in July and October, the peaks in this study occurred in 
February and October. The two peaks imply two distinct generations of the insects in a year 
as suggested by Endrody - Younga (1968). By the same reasoning, the shootflies show three 
generations in a year (Fig. 12), an observation which agrees with the number of generations 
a year of other Chloropidae reported by Cunlife (1925), Sabrosky and Wilbur (1936) and 
Simmonds (1952).
The simultaneous rising and falling of infestation levels makes it possible for both 
shootflies and lepidopterous stemborers to be controlled together, assuming both react equally 
to same control measures. It also suggests that both groups of insects respond similarly to the
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factors influencing their attack on citronella.
Relation between incidence of'deadheart' and Rainfall, Evaporation, Temperature and 
Relative Humidity.
The linear relationships between the infestation rates and the above-mentioned climatic 
factors are rather weak, implying weak influences of these factors on infestation. 
Nevertheless, rainfall appears to be the dominant factor impacting on both groups of insects. 
Thus, infestations are always low in high rainfall and vice versa (Fig. 14).
The low infestations from April to July indicate that low populations of the larvae 
attack the crop during periods of high precipitation. In the case of the lepidopterous 
stemborers, this agrees with the observation of Jerath (1965) in Nigeria, who reported very low 
larval density of R. saccharina during the wet season. Also low infestation in the period above 
supports the suggestion by Easwaramoorthy and Jayaraj, (1988) that high amounts o f rain 
might be directly responsible for less borer incidence. In this work, high level of surface run­
off occurred in both Farms A and B during high precipitation and since the exit/entry holes 
were so low above the ground surface, the tunnels became susceptible to flooding, thus 
rendering the larvae vulnerable during heavy and continuous rains. This probably contributed 
to the absence of damage by the stemborers during the rains (Fig. 14). The gradual build up 
of infestation by the larvae of the chloropids from August could imply corresponding build 
up of adult population from the end of the rainy period in July (Fig. 14), which would agree 
with the conclusion by Sabrosky and Wilbur (1936) that adult chloropids emerge after periods 
of heavy rains. It is, however, at variance with the findings of Cunlife (1925), and Simmonds
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(1952) which show no such relationship with rainfall.
There was a sharp drop in infestation by both groups of insects from November to 
December, when evaporation was very high and there was no precipitation (Fig. 14). In the 
case of the shootflies, this implies that there are very few adults during drought conditions as 
was reported for other chloropids (Sabrosky and Wilbur, 1936). During this period the plants 
are perhaps too dry to attract and support the insects.
The influence of the relative humidity and temperature on the shootflies was not so 
obvious, considering the relatively very low fluctuations in their trends as the infestation 
fluctuated (Fig. 14). However, their effects might be reflected in the influence of evaporation, 
since evaporation is the combined effects of temperature and relative humidity (Messenger, 
1959). Balraj et al (1977) observed that high temperatures are lethal to the larvae and eggs of 
lepidopterous shootborers, especially Chilo partellus and Adeyemi (1969) reported that larvae 
of Sesamia calamistis undergo dormancy in unfavourably high temperatures. In this work, no 
relationship was found between the stemborers and temperature.
The above results are only preliminary and considering the fact that the pattern of 
attack, especially by shootflies, varies considerably from year to year (Deeming, 1971), the 
seasonal infestations will have to be monitored for more years in order to determine a definite 
pattern in relation to climatic factors.
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CHAPTER FIVE
5.0 ASPECTS OF THE BIOLOGY OF SHOOTFLY,
SCOLIOPHTHALMUS MICANTIPENNIS 
(DIPTERA: CHLOROPIDAE)
5.1. Introduction
As pointed out in the previous chapter, both chloropid shootflies and lepidopterous 
stemborers were important, even though the former caused a higher incidence of'deadheart’. 
Prominent among the chloropids was S. micantipennis which caused the highest level of 
primary damage and so was considered important enough to require further study. 
Information on its biology, which may be useful for its management is lacking. Indeed, most 
of the available information on Chloropidae centres on Oscinella fr it  (L.) in Europe.
For O. frit, Simmonds (1952) reports differences in aspects of the life history, such as the 
number of generations in the year, the length of the various stages, life span and fecundity of the 
adults. In this chapter, attempts were made at studying the reproduction and developmental 
biology in S. micantipennis with the objective of providing useful information for management 
strategies.
5.2 Materials and methods
All experiments were conducted in the laboratory under room temperature of about 27°C 
and relative humidity of 80%.
Mating behaviour and oviposition: The objectives of these studies were to determine 
the following:
1. Frequency of mating
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2. Time of mating
3. Duration of mating
4. Interval between last mating and oviposition
5. Oviposition sites
6. Nature of eggs laid
7. Batch size of eggs
8. Incubation period
9. Hatchability of eggs.
Cut citronella shoots with leaves were placed in 15.3cm x 2.6cm glass tubes containing 
moist cotton wool to keep the tillers fresh. Newly emerged adults o f S. micantipennis, reared 
from infested citronella tillers, were etherized and their sexes determined using their external 
genitalia. A male and female pair was introduced into each tube. The tubes were covered with 
a fine net held in place by a rubber band (plate 5), left in the laboratory and inspected daily at 30- 
minutes interval starting from 0700 hours to 2000 hours GMT. Each morning the insects were 
momentarily immobilized by placing the tubes in a freezer for about one minute, and the 
citronella shoot and cotton wool removed and inspected under the microscope for eggs. 
Temperatures at 0900 hours and 1500 hours were recorded and used to calculate the mean daily 
temperature. A total of 45 pairs of S. micantipennis were observed.
Twenty tubes without citronella shoots were also supplied with a pair of adult S'. 
micantipennis each and inspected as above. Also insect pairs were confined to the leaves of 
potted citronella plants in 15 tubes. A section of the leaf was confined together with insects
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inside a 10 x 2 cm tube which had the two open ends plugged with cotton wool such that the 
proximal and distal ends of the leaf remained outside the tube. Insects were fed on 10% sugar 
solution. In all the above experiments the insects were inspected till they died. A search for 
oviposition sites was conducted in the field using hand lens to carefully inspect the total surface 
of both healthy and 'deadheart’ tillers for eggs.
Larval stage: Unidentified larvae from infested tillers were removed, classified 
arbitrarily as young and old, and reared separately in petri dishes by placing them singly between 
fresh sheaths of citronella. Every morning the sheath was spread out and washed in tap water in 
a petri dish and the water inspected under the microscope for exuviae. The idea was to trace the 
development of S. micantipennis from larvae collected from the field since no eggs could be 
obtained from the laboratory or field. The arbitrary classification was unscientific. It was 
nevertheless used because the instars were not known and also could not be identified by Dyar’s 
law, due to the unavailability of information on larval sizes, measurements of which had to stop 
because of the unacceptably high death rate in the delicate larvae when exposed under the 
microscope.
Pupal stage: Larvae in advanced stage of development, not feeding and less mobile, that 
is about to pupate were collected from infested citronella tillers and put singly in 15.3 x 2.6cm 
glass tubes containing wet cotton wool. The tube was covered with a cork and inspected daily 
at 0700 hours and 1500 hours. The date they started developing puparia was recorded. Their date 
of emergence was also recorded and the sex determined by examining the external genitalia. The 
lengths of the puparia were measured using an eyepiece micrometer fitted to a microscope.
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Plate 5: Experiment to determine oviposition site of Scoliophthalmus micantipennis in die
laboratory
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Adult Longevity: This study was to determine the life span of the adult male and female. 
Fifty-three pupae made up of 24 male and 29 female from infested tillers in the field were put 
singly in 7.7 x 2.6cm tubes. They were inspected daily at 0700 hours and 1500 hours until they 
emerged and died. The insects were fed on 10% sugar solution soaked in cotton wool and the 
tubes were covered with fine cloths held in place by rubber band.
Sexual dimorphism in adults: Observation from laboratory rearing showed that adult 
specimens of the shootflies occurred in two distinct groups; smaller specimens and bigger ones. 
Therefore, 30 small and 31 large specimens of S. micantipennis which were freshly killed in 
ethyl acetate were measured from head to abdomen, using an eyepiece micrometer fitted to a 
microscope. The idea was to determine if there existed any sexual dimorphism in species.
5.3 Results
Mating behaviour and oviposition: Out of 80 set-ups, only two pairs of insects were 
found mating in tubes with cut citronella shoots. The first pair stayed in copula between 0700 
hours and 0912. The second pair stayed in copula between 1100 hours and 1417 hours. In both 
cases the male mounted the female on the latter’s back between the wings. The male bent the tip 
of its abdomen until its extruded copulatory organ was inserted into the genital opening of the 
female. They remained in copula even when disturbed. The females mated within one and 17 
days after emergence and died between 3 and 8 days later respectively. The males also mated 
within one and 17 days after emergence but died 2 days later. No eggs were found laid in any of 
the experiments.
Larval stage: No exuvia was detected in any of the 53 set-ups. Thirty-four out of the
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37 'young’ ones died by the seventh day, and four of the 16 'o ld’ ones died while 12 pupated 
within five days (Table 6).
Table 6: Survival and Development of larvae of Shootflies collected from infested tillers
Classific Total State of Day(s) after collection
Ation No. of Larvae 1 2 3 4 5 6 7 8 >9
Larvae
'Young’ Dead 17 22 28 30 32 34 34 34 34
37 Pupated 0 0 0 0 0 0 0 2 3
'O ld’ Dead 1 1 2 2 4 4 4 4 4
16 Pupated 9 9 10 10 12 12 12 12 12
Pupal stage: The pupa was exarate adecticous. This means it had no functional mandibles 
to use in escaping from the puparium and also the appendages were free of any secondary 
attachment to the body. It was also coarctate which means it was enclosed in paparium formed 
from the preceding larva. The pupa initially was pale but this changed to deep brown after a day 
or two. The length of the puparium of the female ranged between 2.3mm and 3.9mm with a mean 
of 3.3±0.1mm (n=30) and that of the male ranged between 2.2mm and 3.9mm with a mean length 
of 3.2±0.01 mm (n=30) (Table 7). There was no significant difference (P > 0.05) between the 
lengths of male and female puparia but the male puparium had bands of striations which were 
absent from the female one.
The pupal periods ranged between 4 and 9 days with a mean of 6.7 ±0. 4 days (n=22) for 
females and from 4 to 13 days with a mean of 7.2±0.1 days (n= 17) for males (Table 8). There was 
no significant difference (P > 0.05) between them (Table 8). At the end of pupation, the puparium 
of both sexes split horizontally at one end and a small cap opened at the end of the split (Fig. 20
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and Fig. 21) from which the adult emerged. This happened in both sexes.
Table 7. Length of empty puparia of female and male Scoliophthalmus 
______ ______ micantipennis.
Total ^58df;
Number Range in Mean length P = 0 .0 5
Sex of Length (mm) (x ± S.E.)mm
puparia
(n)
Male 30 2 .1 8 -3 .9 2 3.16 ±  0.08
Female 30 2 .2 3 -3 .9 4 3.32 ±0.08 n.s
Table 8: Pupal period of male and female Scoliophthalmus micantipennis in the 
laboratory at 27.4°C
Total 3̂7dfj
Number Range in Mean length P = 0 .0 5
Sex of Length (mm) (x ± S.E.)mm
puparia
(n)
Male 17 4-13 7.24 ± 0.49
Female 22 4-9 6.72 ± 0.39 n.s
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*  4 0
Dorsal vieH, of
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X 40
Fig. 21: Dorsal view of female puparium of Scoliophthalmus micantipennis with the tip 
broken to provide passage for the emerging adult.
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Adult longevity: There was no significant difference (P > 0.05) between the survival 
periods of the sexes; the female lived for 8.6 ± 0.8 (n = 29.) and the male 9.4 ± 0.6 
days (n=24) after emergence (Table 9). The newly emerged adults were pale with shorter wings. 
The body however, became darker and the wings longer, later.
Table 9: Longevity of adult male and female Scoliophthalmus micantipennis in the 
laboratory at 2 7 .4 ° C ._____________________________________________
Total tsidf*
Number Range (days) Mean longivity P =  0 . 0 5
Sex of insects (x ± S.E.) days
(n)
Male 24 4-15 9.41 ±0.60
Female 29 1-17 8.59 ±0.77 n.s
Sexual dimorphism in adults: Results of the measurements of the lengths of 30 small and 
31 large specimens (measured from head to abdomen) are given in Table 10. The length of the 
small ranged from 1.9mm to 2.5mm with a mean of 2.0 ±.0 mm; that of the large ones ranged 
between 2.4mm and 3.3mm and the mean was 3.0±0mm. It was found that all smaller specimens 
were males while the larger ones were females. Their lengths were significantly different (t = 
5.226, p <  0.05).
Table 10: Total length of adult male (small) and female 0 arge) Scoliophthalmus
micantipennis
Total T5idr;
Number Range in Mean length P = 0 . 0 5
Sex insects Length (mm) (x ± S.E. (mm)
(n)
Male (small) 30 1.96 ±0.02
Female (large) 31 2 .4 -3 .3 2.98 ±0.03 *5.226
* Significant at p < 0.05
1
N
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5.4 Discussion
Mating behaviour and Oviposition: In contrast to the report by Simmonds (1952) 
that Chloropidae such as O. frit mate readily on emergence, only 2 pairs of S. micantipennis 
mated in this study. That S. micntipennis remained in copula for a long time (over 2 hours), 
however, agrees with Simmonds’ (1952) observation. Even though the low number o f insects 
that mated makes it difficult to draw definite conclusions, the long copulation period observed 
may provide opportunity for attacking them with contact insecticide during their mating 
season. The male is smaller (mean = 2.0 ± 0mm) than the female (mean = 3.0 ± 0mm) making 
it convenient for the female to carry the male on its back during mating. Despite this apparent 
convenience, the mating did not appear to have been a productive one since it did not result 
in oviposition. The observation that no eggs were laid in captivity cannot be attributed to the 
inability of the insects to mate as a result of wrong identification since even in situations where 
mating took place, no eggs were laid. Although oviposition in Chloropidae is unpredictable 
(Aldrich, 1920), the observation in this study was probably due to unsatisfactory conditions 
in captivity. This is because workers such as Aldrich (1920), Steel (1931) and Simmonds 
(1952) who succeeded in their studies on mating and oviposition in O. fr it had to rigidly 
control the temperature and r.h. at 24°C and between 90-100 percent, respectively. This could 
however, not be done in this study and might have contributed to the failure to achieve 
oviposition.
Larval and Pupal development: Studies on the larval stages did not yield the desired 
results because of high mortality. For instance, over 90% of the ‘young’ larvae died by the
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seventh day (Table 6). Deeming (1971) also reported high death rate of larvae of Chloropidae 
and listed the problem as one of the major difficulties hampering the studies of the immature 
stages of the chloropid shootflies.
In the pupa, the presence of striations on the male puparium is probably the 
only observable difference between the sexes, since there is no significant difference (p > 0.05) 
between their lengths. However, Goodlife (1942) found sexual dimorphism in the lengths of 
other chloropids such as Chlorops pumilionis Bjerk. The pupal period (4 - 1 3  days) of S. 
micantipennis as observed in the present study shows wider variation than the 9-10 days 
reported by Simmonds (1952), for O.frit. probably as a result of the variability of larval stages 
collected for the study.
Adult: Even though not many morphological characters were measured, it was found that 
the total lengths of the adults differed significantly (t = 5.226: p < 0.05) between the two sexes. 
Thus the adult S. micantipennis exhibit sexual dimorphism in their lengths, the males are shorter 
than the females. Sexual dimorphism in body lengths has also been reported by Goodlife (1942) 
in adult C. pumilionis and has been used for taxonomic purposes. Sexual dimorphism, therefore, 
appears to be a common phenomenon in the Chloropidae. The range in body length of 1.9 -  
3.8mm of S. micantipennis found in the study, falls within the 1.5 -  5.0mm range for Chloropidae 
reported by Sabrosky (1962). The adults of S. micantipennis survived for about the same period. 
However, the range of the survival of the females was rather wide. The early deaths might have 
been caused by some pathogenic infection.
Not much could be obtained for the life cycle of S. micantipennis in this study, but as the 
major primary feeder of citronella, there is the need for complete information on the life history 
which may be taken up in further work.
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CHAPTER SIX 
SUMMARY AND CONCLUSIONS
Summary
Two species of aromatic citronella, Cymbopogon nardus and Cymbopogon winterianus 
were introduced into Ghana from Asia by Lever Brothers Ghana (GH) Ltd. (LBG) in 1978 
and cultivated by farmers. By 1988 insects had started attacking the crop, but no detailed 
work has been done on the insect pests. This work was therefore undertaken to provide 
detailed information on the pests that could be used for their management.
Data were collected from 12 farms in the Eastern and Greater Accra regions all in the south­
eastern part of Ghana where the crop is extensively grown. However, the greater part of
.. — * - 
the work was done at Osofoiaman near Pokuase in Greater Accra. Two farms were used
initially but one had to be abandoned due to flooding.
Sweeping was done intensively for eleven months in one farm and extensively in six others 
for three months to survey insects associated with the shoot of citronella.
Random sampling for 'deadheart’ was done for one year at Osofoiman. The insect feeders 
were identified and the incidence of their damage in relation to climatic factors was 
monitored for one year. A comparison of the rate of infestation was made using two 
methods namely, ’deadheart’ symptoms and random dissection of shoots.
Studies on some aspects of the reproductive and developmental biology of the major 
chloropid shootfly S. micantipennis were also done in the laboratory.
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6.2 Conclusions
It was found that the vegetative portion of citronella was associated with diverse insect 
fauna: insects comprising 10 orders and 103 families visit citronella. Among these insects, those 
that damage citronella are the shootflies (Dipterea: Chloropidae) and stemborers (Lepidoptera: 
Noctuidae and Pyralidae) and termites. The chloropid shootflies are Scoliophthalmus 
micantipennis, Scoliophthalmus trapezoides, Anatrichus pygmaeus, Aprometopis flavofacies, 
Elachiptera occipitalis and a yet to be identified chloropid shoot fly. The lepidopterous stemborers 
are Sesamia sp (Fam: Noctuidae) and Eldana saccharina (Fam: Pyralidae) while the termites are 
yet to be identified. The shootflies and stemborers are equally important as far as damage to the 
tillers is concerned.
The primary feeders are S. micantipennis, A. flavofacies, Sesamia sp. and E. saccharina. 
Scoliophthalmus trapezoides is considered as both primary and secondary feeder. The major 
feeder among the primary feeders of citronella is S. micantipennis because it is the greatest number 
of insects causing primary damage.
Damage to the tillers of citronella is done by the larvae of the shootborers. They tunnel the 
tiller to cause the inner whorl to wilt and become pale resulting in the 'deadheart’ symptom. The 
larvae live inside the tillers and so can possibly be controlled by systemic insecticides. The 
incidence of the damage was found to have weak linear relationship with relative humidity or 
temperature or evaporation or rainfall. It shows two possible peaks for both the stemborers and 
shootflies. It is also low between January and July, and high between August and November. 
There is synchronisation in the build up of the incidence of damage by both groups of shootborers.
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It is therefore recommended that they are controlled simultaneously.
Farms that are over one year old appear susceptible to termite attack; farmers should 
therefore not cultivate one farmland for too long but if they do, they should start control measures 
against termites early, about one year after cultivation. Also, whenever there is outbreak of the 
grasshopper, Zonocerus variegatus, preventive measures should be taken for the insects could 
attack the plant.
It has been found in the study that improved sweep' net locally designed is more effective 
in sampling insects on citronella. It is by no means perfect and it needs some improvement to 
increase its efficiency. For example, the opening should be enlarged because during sampling it 
was found to be too narrow especially for the very swift insects. The handle also needs 
lengthening. It is found that the shortness of the handle made the user bend too low.
As much as possible, experimental farms should be established for such future studies so 
that many experiments and also random dissection can be carried out to get the true infestation of 
the insects. This is because this study has shown that infestation as determined only by 'deadheart’ 
symptom is an underestimation of the true situation by about 32%.
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Original not seen
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APPENDICES
Appendix 1: Average of climatic factors at Osofoiaman over 5 years (1987-1991)
Month Mean Mean Temperature (°C) Relative Humidity
Rainfall Evaporation (%)
(mm) (mm)
Mean Mean 0900 Hrs 1500 hrs
Maximum Minimum
January 8.84 1.95 33.84 20.65 88 70
February 20.68 2.4 34.7 23.6 89 70
March 43.32 2.58 34.44 23.13 89 74
April 60.48 2.58 34.42 23.3 89 72
May 202.38 1.85 33.22 22.92 90 78
June 153.44 1.3 31.9 22.44 90 82
July 119.7 1.13 30.04 21.96 93 86
August 60.88 0.93 29.25 22.2 94 88
September 106.22 1.0 30.76 22.5 90 82
October 91.16 1.22 31.56 22.08 90 82
November 91.52 1.33 32.74 22.48 89 82
December 35.26 1.63 32.96 21.16 92 78
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FEB. MARCH APRIL JUNE JULY AUG. SEPT. OCT. NOV. DEC.
II HOMOPTERA
Flatidae
Cicadellidae
Cercopidae 23 33 25
Dictyoptera
HEMIPTERA
Scutelleridae
Pentatomidae
Brachyplatidae
Pyrrhocoridae
Reduviidae
II DERMAPTERA
Forficulidae
ORTHOPTERA
PvreomorDhidae
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Appendix 3: Sweep net collection of insects associated with citronella in the other 
farms, October- November, 1992.
Insect F a r m
DIPTERA Osofoia- Botoku Selina- Ababio Omenako Kpan-
Man Taylor kpan
Farm C Ayik-
uma
Chloropidae 153 89 72 75 29 71
Cecidomycidae 1 - ■- - 3
Tephritidae - 3 3 5 8
Lonchaeidae 1
Agromyzidae 3 - 1
Dolichopodidae - 3 - 2
Curtonotidae - 1 6 3 -
Platystomatidae - - - 2
Ottidae - - 1
Pipunculidae - - 1
Ceratopogonidae - 1 1
Empididae - 5
Chamaemyiidae 1 -
Drosophilidae 1 3
Muscidae 16 11 3 7 35
Sarcophagidae 1 - 9
Sepsidae 1 - 1 -
Sciaridae 2 - 18
Phoridae 2 2 - 3 1
Mycetopilidae 1 1 .- - -
Heleomyzidae 1 4 - 1
Lauxaniidae 1 2 2 7 -
Asteiidae 2 - - 2
Sciomyzidae - 1 -
Culicidae - 1 1 -
Syrphidae 1 4
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Appendix 3 continued.
Scatopsidae - 2 - - 6
Piophilidae - - - 1 -
Dixidae - - - - 4 -
Calliphoridae 1 - 1 - - 1
Ephydridae 7 - - -
Dichlopodidae - 2 2 -
HYMENOPTERA
Formicidae 205 440 109 139 139 241
Evaniidae 2 4 2 4 2
Ichneumonidae 4 3 - - -
Tiphiidae 2 1 2 1 -
Bracondiae 10 4 9 20 13 7
Vespidae - 1 1 1
Eulophidae 1 2 5 4 2 3
Mymaridae - 1 1
Erytomidae - 3 2 • 2 4 4
Encycrtidae 1 3 1 2 1
Eupelmidae 2 1 3 1
Dryinide 1 2
Agaonidae 1 2 1 4 - -
Pteromalidae 5 2 11 10 5 1
Sphecidae 2 1 3 5 1 2
Chalcidae 7 - 4 3 26 1
Prototrupidae 1 1 -
Bethylidae 3 - -
Colletidae 1 1 1 -
Diapriidae 1 -
Torymidae 1 28 2 1 1
Eucharitidae 1 -
Perilampidae 1 2 2 6 1
Pompilidae - - - 2 1
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Appendix 3 continued.
Platygasteridae • - 1 -
Andrenidae 1 - - - -
Cynipidae - - - 1
Ceraphronidae - - - - - 2
Gasteruptiidae - - 1 - -
COLEOPTERA
Chrysomelidae 7 1 - 2
Curculionidae 4 3 5 7
Cerambycidae 2 - 8
Coccinellidae 1 1 1 -
Lagriidae 8 2 7 1 1 6
Meloidae 4 - -
Pselaphidae 1
Elateridae - 2 1
Anthribidae - 6 - -
Staphylinidae - - 1 1
LEPIDOPTERA
Noctuidae 2 3 1 1
Coleophoridae 2 - 1 1 - -
DICTYOPTERA
Mantidae 1 2 1 4
Blattidae 1 6 2 • 2 - 1
DERMAPTERA
Forficalidae 5 1 2 1 2
NEUROPTERA
Chrysopidae - 1 4 2
Myrmeleontidae - 1 -
Coniopterygidae - - - 2
ORTHOPTERA
Pyrgomorphidae 62 51 20 29 12 6
Tettigonidae 7 6 4 6 4
Gryllidae 10 10 - - 6 4
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Appendix 3 continued.
HEMIPTERA
Corimelaenidae 1 9 1 - 12
Pentatomidae 2 1 2 2
Lygaeidae - 1 21 35 13 5
Reduviidae 1 - 1 • _ 1
Scutelleridae 1 - 3
Tingidae 1 1 2
Rhopalidae - 5 11
Miridae - 3 3 7 3
Nabidae 4 3
Piesmatidae - 1
Coreidae - - 2 1
Alydidae - - 1
HOMOPTERA
Cercopidae 129 33 92 153 24 17
Cicadellidae 64 115 259 90 124 324
•
Delphacidae 2 2 1 8 51 61
Flatidae 1 1 8 2
Aphididae 1 5 6 8 18
Membracidae - - 1 _
Dictyopharidae 1 2 8
Psyllidae 2 - 1
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Appendix 4: Key to shoot fly species recorded from citronella tillers
The adult Chloropidae are small flies - for example, the species identified in the survey ranged between 
1.9mm and 3.8 mm and Sabrosky (1962) puts the size as ranging between 1.5 and 5.0mm long. The 
head has characteristically well developed ocellar triangle. The bristles on the body are reduced and so 
also is the wing venation. The insects have an incomplete subcostal vein and the costal vein is broken 
near the end of R,. The adult Lonchaeidae have a complete subcostal vein. The key below is meant to 
provide an easier and quicker way of identifying the species identified in this study without having to 
go through long keys which may not be available anyway.
1 Subcostal vein complete................Lonchaeidae (Silbapectita] -
Subcostal vein not complete ........................... 2
2 Body predominantly black. Mesopleuron haired ........................................ 3
Body of various colours other than black.
Mesopleuron bare .......................................6
Subcosta continues beyond apex of M]+2 .......................................4
Subcosta does not go beyond M,+2 but just beyond
apex of R4+5 ................. Scoliophthalmus trapezoides
4 Mesonotum and Scutellum thickly beset with long erect
spine like bristles. Tergites fused .................................... Anatrichus pygmaeus
Mesonotum and scutellum without long erect spine
like bristles <
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Arista thickened and flattened body, wings and legs more or
less narrowly enlongated .....................Species D
Arista not thickened and not flattened. Body, wings and legs reltively short. Haltere
with black knob. Hind cross-vein strongly oblique.............................. Scoliophthalmus
micantipennis.
Body predominantly dark brown. Facial carina absent. Scutellum flattened and 
trapezoidal ................................ Elachiptera occipitalis
Body predominantly bright yellow with 4 dark.horizontal bands at the dorsal part of 
the thorax. Scutellum flattened and rounded facial carina present
.............................Aprometopis flavofacies
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Appendix 5: Chi-square analysis of adult Diptera reared and Lepidoptera larvae collected 
from tillers showing various forms of 'deadheart'.
Insect Count Early Advanced Secondary Row
Total
Scoliophthaim us trapezo ides 1 21 35 8 64
28.2%
Scoliophthalmus micantipennis 2 39 6 45
19.8%
Anatrichus pygmaeus 3 14 32 46
20.3%
Elachiptera occipitalis 4 3 3
1.3%
Aprometopis ilavofacies 5 5 5
2.2%
Species D 6 8 24 32
14.1%
Silba pectita 7 3 1 4
1.8%
Phoridae 8 10 5 15
6.6%
Sesamia sp 9 11 11
4.8%
Eldana saccharina 10 2 2
0.9%
Column 78 76 73 227
Total 34.4% 33.5% 32.2% 100.0%
Chi-square
192.29033
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1 0 1
Appendix 6: Comparison of rate of infestation estimated from only 'Deadheart' symptoms and 
from random dissection of shoots at four different farms.
Infestation rate of tillers (%)
Farm Only 'Deadheart1 Dissection
Osofoiaman (Farm B) 0.27 0.82
Ashalaja 2.14 2.61
Omenako 0.28 0.4
Ababio's 0.4 0.7
Appendix 7: Daily Growth of healthy and infested tillers after ratooning
Height of tillers of Hill 13 Height of tillers of Hill 17 Height o f tillers o f Hill 30 
Day (mm) (mm) (mm)
Healthy Infested Healthy Infested Healthy Infest- ed
1 3.0 4.10 2.87 3.50 2.25 2.0
2 5.17 6.70 6.70 5.20 4.62 4.30
3 8.45 9.30 9.30 6.50 7.65 6.3
4 12.25 11.20 11.20 9.0 11.4 8.0
5 16.33 16.0 16.0 11.0 14.5 11.5
6 19.50 17.0 17.0 12.4 16.42 15.0
7 24.33 18.0 18.0 13.0 20.0 19.0
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Appendix 8: Weekly percentage 'deadheart' by shootflies and stemborers, 
Osofoiaman farm A, January-June, 1991
Date Percentage 'Deadheart'
Lepidoptera (%) Diptera (%)
28/1/91 0.2 0.2
4/2 0 0
11/2 0 0.18
18/2 0.25 2.01
25/2 1.17 1.5
4/3 0.41 0.81
11/3 0.18 0.18
18/3 1.7 2.33
25/3 0.15 0.15
% 0.15 2.3
8/4 0.23 0.62
15/4 0.30 0.23
22/4 0 0.23
29/4 0.23 0.08
6/5 0.08 0.38
13/5 0.31 0.15
20/5 0 0.31
27/5 0.15 0.46
3/6 0 1.38
10/6 0 0.99
17/6 0 0.23
24/6 0 0.34
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Appendix 9: Weekly percentage 'deadheart' by shootflies and stemborers, 
Osofoiaman Farms B,
1991 ______
Date Percentage 'Deadheart'
Lepidoptera (%) Shootflies (Diptera) (%)
12/2/91 0.73 1.76
19/2 0.43 0.97
26/2 1.82 1.43
5/3 0 0
12/3 0.73 0
19/3 0 0
26/3 0 0.23
2/4 0 0.15
9/4 0 0.08
16/4 0 0
23/4 0 0.23
30/4 0 0.31
7/5 0 0.54
14/5 0 0
21/5 0 0.08
28/5 0 0.15
4/6 0 1.69
11/6 0 0.92
18/6 0 0.15
25/6 0 0.69
2/7 0 0.92
9/7 0 0.15
16/7 0 0.23
23/7 0 0
30/7 0 1.7
6/8 0 1.15
13/8 0 3.3
20/8 0 2.34
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Appendix 9 continued.
27/8 0 1.3
3/9 0 3.6
10/9 0.07 2.75
17/9 0 3.5
24/9 3.25 2.19
1/10 3.86 1.3
8/10 1.06 3.3
15/10 3.7 3.56
22/10 4.41 6.88
29/10 1.66 2.5
5/11 0.74 1.04
12/11 0.53 1.07
19/11 0.72 0.36
26/11 1.56 0.29
3/12 0.78 0.14
10/12 0 0
17/12 0 0
Appendix 10: Mean monthly Temperature, Rainfall, R.H and Evaporation at 
Osofoiaman 1991
Mean Relative Mean Mean Mean Rainfall 
Humidity (%) Evaporation (mm) Temperature (mm)
(°c)
January 82 1.5 28.1 30.8
February 81.5 1.8 29.1 4.4
March 80 2.3 29.1 21.4
April 81 1.8 28.6 109.7
May 84 0.9 27.8 500.7
June 89 0.8 27.8 154.8
July 91 0.6 26.1 251.7
August 91.5 0.5 25.5 37.6
September 87 0.9 26.7 22.5
October 85.5 1.2 26.8 50.2
November 85 1.4 27.6 27.6
December 83.5 1.9 27.5 4.5
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Appendix 11 : Regression analysis matrix of percentage 'deadheart' by lepidopterous 
stemborers
on Rainfall.
Response variate LP
Fitted terms Constant, RF
Summary of analysis
d.f. s.s m.s. v.r Fpr.
Regression 1 5.54 4.543 3.77 0.059
43 51.81 1.205
44 56.36 1.281
-1 -4.54 4.543 3.77 0.059
Percentage variance accounted for 5.9 
Estimates of regression coefficients 
estimate s.e. t tpr.
Constant 0.6298 0.210 3.97 <.001
RF -0.0017 0.00115 -1.94 0.059
Appendix 12 : Regression analaysis matrix of percentage 'deadheart' by dipterous 
shootflies
on Rainfall
Response variate DP
Fitted terms Constant, RF
Summary of analysis
d.f s.s. m.s. v.r. F pr.
Regression 1 5.54 4.543 3.7 0.059
43 51.81 1.205
44 56.36 1.281
Percentage variance accounted for 6.9 
Estimates of regression coefficients
estimate s.e t r pr. 
Constant 1.3413 0.265 5.73 <001 
RF -0.0024 0.00145 -2.06 0.046
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Appendix 13 : Regression analysis matrix of percentage 'deadheart' by dipterous shootflies 
on Evaporation
Response variate DP
Fitted terms : Constant, EV
Summary of analysis
d.f. s.s. m.s. v.r. F pr.
Regression 1 6.29 6.286 3.77 0.059
43 84.30 1.960
44 90.59 2.059
Percentage variance accounted for 6.9
Estimates of regression coefficients
estimate s.e. t tpr.
Constant 2.2639 0.437 4.27 <.001
EV -0.8958 0.325 -1.79 0.080
Appendix 14 : Regression analysis matrix of percentage 'deadheart' by dipterous
shooflies
on Temperature.
Response variate : DP 
Fitted terms : Constant, TP
Summary of analysis
d.f. s.s. m.s. v.r. F pr.
Regression 1 17.94 17.944 10.62 0.002
43 72.64 1.688
44 90.59 2.059
Percentage variance accounted for 17.9 
Estimates of regression coefficients 
estimate s.e. . t tpr.
Constant 17.15 4.90 3.50 <001
TP -0.5826 0.178 ■3.26 0.002
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Appendix 15 : Regression analysis matrix of percentage 'deadheart' by dipterous shootflies 
on Relaltive Humidity
Response variate : DP
Fitted terms : Constant, RH
Summary of analysis
d.f. s.s. m.s. v.r. F pr.
Regression 1 7.66 7.659 3.97 0.053
43 82.93 1.929
44 90.59 2.059
Percentage variance accounted for 6.3 
Estimates of regression coefficients
estimate s.e. t t pr.
Constant -9.8968 4.69 -1.74 <.001
RH -0.1292 0.0548 -1.99 0.053