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SPECIES COMPOSITION AND HOST ASSOCIATION OF THRIPS
(THYSANOPTERA) IN THE EASTERN AND GREATER ACCRA
REGIONS, GHANA
BY
CHIA SHAPHAN YONG
(10444692)
BSc. (HONS) ZOOLOGY AND MEDICAL LABORATORY TECHNOLOGY
(UNIVERSITY OF BUEA, CAMEROON)
A THESIS SUBMITTED TO THE UNIVERSITY OF GHANA, LEGON IN PARTIAL
FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF
PHILOSOPHY (M.PHIL.) DEGREE IN ENTOMOLOGY
AFRICAN REGIONAL POSTGRADUATE PROGRAMME IN INSECT SCIENCE
(ARPPIS)* UNIVERSITY OF GHANA, LEGON-ACCRA GHANA
JULY, 2015
* JOINT INTER-FACULTY INTERNATIONAL PROGRAMME FOR THE
TRAINING OF ENTOMOLOGISTS IN WEST AFRICA.
COLLABORATING DEPARTMENTS:
ANIMAL BIOLOGY AND CONSERVATION SCIENCE
(SCHOOL OF BIOLOGICAL SCIENCE)
AND
CROP SCIENCE (SCHOOL OF AGRICULTURE)
COLLEGE OF BASIC AND APPLIED SCIENCES
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DECLARATION
I hereby declare that this thesis is the result of the original research work I, Chia Shaphan
Yong personally carried out for the award of Master of Philosophy (M. PHIL.) in
Entomology at the African Regional Postgraduate Programme in Insect Science (ARPPIS)
from the University of Ghana, Legon. All references to other people’s work have been duly
acknowledged and the thesis has not been submitted in part or whole for the award of a
degree elsewhere.
Signature----------------------------------Date--------------------------------------
CHIA SHAPHAN YONG
(Student)
Signature------------------------------------Date-------------------------------------
PROF. EBENEZER ODURO OWUSU
(Supervisor)
Signature------------------------------------Date----------------------------------------
DR. VINCENT YAO EZIAH
(Supervisor)
Signature---------------------------------------Date-------------------------------------
DR. ROSINA KYEREMATEN
(ARPPIS Coordinator)
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ABSTRACT
Thrips are crop pests causing damage to a wide range of crops ranging from fruits to
vegetables to ornamentals through direct feeding or oviposition on plants. The main objective
of this study was to determine the species composition of thrips and their host range in some
selected parts of Greater Accra and Eastern Regions of Ghana. Thrips were collected from
flowers, leaves and twigs of vegetable, ornamental and tree crops by beating and jarring and
identified to species level. Fifty sticky traps comprising 25 each of Blue and Yellow traps
were also set in vegetable farms for 7 months, September 2014 to March 2015 to trap thrips
species. Data on average daily temperature and rainfall were collected from the Ghana
Meteorological Agency located at Mempasem in the Greater Accra Regionand used to
establish their relationship with trap catches. Farmers’ knowledge of thrips and their pest
management practices was assessed using a survey questionnaire. Abundance of thrips was
studied on vegetable crops and within plant distribution of Thrips palmi determined on
cucumber plants. Over twenty species of thrips were recorded. Major thrips species recorded
include; T. palmi, Megalurothrips sjostedti, Frankliniella schultzei and Thrips tabaci. In all,
13367 adult thrips were captured by traps. Individual trap types were 8206 (61.4%) and 5161
(38.6%) by the Blue and Yellow traps, respectively. Generally, there was no significant
difference (P =0.363, DF = 1, P>0.05 = α) among trap catches. Both rainfall (R2 = 0.0142, P
= 0.530, P > 0.05 = α) and temperature (R2 = 0.0603, P = 0.191, P > 0.05 = α) were not
significantly correlated to trap catches. However, the number of thrips in sticky traps from
one locality (East Legon) was significantly positively correlated (R2 = 0.1346, P = 0.0461, P
<0.05 = α) with average weekly temperature. Only 29% of the farmers interviewed knew
thrips and had experienced thrips on their crops. Survey results showed a 100% reliance on
chemical pest control by farmers with most of them dependent on personal experience for
agronomic practices.
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Mean number of thrips was significantly higher (Fpr =0.012, DF = 12, P < 0.05 = α, LSD =
1.15) on eggplant and cucumber compared to other vegetables examined.  Four plant species
including eggplant, cucumber, gboma and sweet pepper were examined for thrips abundance
recorded T. palmi infestation. Even though there was no significant difference (Fpr = 0.6292,
P > 0.05) among thrips counts from various plant species, more adult T. palmi were recorded
on cucumber leaves. For within plant distribution, there was a significant (Fpr = 0.0036, P <
0.05) difference among mean numbers of thrips on young, middle and bottom leaves, with
counts from young (mean = 16.1) and middle (mean = 10.1) leaves significantly higher (q =
5.337 > q-critical =3.532, α = 0.05) compared to the bottom (mean =3.2) leaves.
In conclusion, several species of thrips infest vegetable and ornamental plants in Southern
Ghana and are polyphagous insects, infesting a wide range of plants species. Thrips palmi
was recorded in Ghana for the first time. Knowledge of thrips was very limited among crop
growers. The improvised sticky traps were effective in capturing thrips, thus may be good for
monitoring early and small thrips populations in the field.
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DEDICATION
I dedicate this work first to the Almighty God for his sufficient grace over my life and to my
family.
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ACKNOWLEDGEMENTS
I am grateful to God Almighty for leading me through this two-year programme.  I owe a
great debt of gratitude to my supervisors: Prof. Ebenezer Oduro Owusu and Dr. Vincent Yao
Eziah for their guidance and training which helped me to complete this project.
I thank the ARPPIS Curator, Mr. Davis Henry who helped me throughout this project in
identifying thrips species and also training me on how to collect thrips and prepare permanent
slide mounts of them in the laboratory. I thank all the ARPPIS lecturers for the theoretical
and practical training given me, especially Dr. Maxwell Billah, the Seminar Coordinator and
Dr. Clement Akotsen-Mensah for their guidance and suggestions in my research work. I
thank the ARPPIS Coordinator, Dr. Rosina Kyerematen for her administrative assistance. I
thank the ARPPIS teaching and administrative assistants, Ms. Hettie Boafo and Mr. Kwadwo
Boateng who helped me in diverse ways when I needed help.
I thank all the farmers who allowed me access into their farms and those who provided
answers to my survey questions during data collection, especially the Manager of University
of Ghana Farm, the proprietor of Johnco famers, John Kofi, Simon Simif of Aburi Botanical
Gardens, Seidou, and Sulley who showed so much concerned to my work. My heartfelt
thanks go to the Nwenfor and Asaba families for their kind-heartedness and encouragement
during my studies in Ghana.  My sincere thanks go to my family, especially my mother,
Mama Ndisi Judith, my father, Mr. Chia Clement and my siblings Maurice Ngong, Faith
Anyahmbom, Diligence Neng, Derrick Ntaisi and Kestin Tih for their continuous prayers and
encouragement throughout my studies in Ghana. Special thanks to Mr. Ngantu Harrison Ndzi
for immensely assisting me when I applied for this programme. I thank Associate Professor
Helen-Mbufong Kimbi, Dr. Judith-Anchang Kimbi and Dr. Christina Nsuh Konje, all of the
University of Buea, for recommending me for this programme. I thank Mr and Mrs Ndi
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Oswald, for their continuous encouragement during my studies in Ghana. Special thanks to
Angelina Osabutey for assisting me in diverse ways during this project. I also say thank you
to my fellow ARPPIS colleagues; Nimlin Dickson Gabuin, Ayisi Franklin, Micheline
Vignon, Comfort Oseifuah, Dorcas Atibilla, Roger Sigismund Anderson, Peter Okeke, Lami
Jinatu, Ruth Bala, and  Nnenna Onoye. I also thank Eliana Fonsah, Edwin Mustapha, Ebrima
Joof, Sarah-Matio and Derick Asante for helping me in diverse ways during this two-year
programme. I thank Thomas Buxton, Silas Avicor and Mrs. Nkrumah for their kind advice
and assistance during this project. My sincere thanks go to the German Academic Exchange
Service (DAAD), for providing funds for my M. Phil. studies at the University of Ghana,
Legon.
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Table of Contents
DECLARATION ................................................................................................................... i
ABSTRACT ......................................................................................................................... ii
DEDICATION..................................................................................................................... iv
ACKNOWLEDGEMENTS .................................................................................................. v
LIST OF FIGURES ............................................................................................................. xi
LIST OF PLATES ............................................................................................................. xiii
LIST OF TABLES............................................................................................................. xiv
LIST OF ABBREVIATIONS ............................................................................................. xv
LIST OF APPENDICES .................................................................................................... xvi
CHAPTER ONE ................................................................................................................... 1
1.0 INTRODUCTION ....................................................................................................... 1
1.1 Justification ................................................................................................................. 3
1.2 Research Objectives..................................................................................................... 4
1.2.1 Main Objective...................................................................................................... 4
1.2.2 Specific Objectives................................................................................................ 4
CHAPTER TWO .................................................................................................................. 5
2.0 LITERATURE REVIEW ............................................................................................ 5
2.1 Origin and Taxonomy of Thrips................................................................................... 5
2.1.1 Thrips species........................................................................................................ 6
2.2 Biology of thrips.......................................................................................................... 6
2.2.1 General biology..................................................................................................... 6
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2.2.2 Life cycle of thrips ................................................................................................ 7
2.3 Behaviour and habits ................................................................................................... 9
2.3.1 Dispersal behaviour ............................................................................................... 9
2.3.2 Feeding behaviour ............................................................................................... 10
2.3.3 Predation ............................................................................................................. 11
2.3.4 Migration ............................................................................................................ 12
2.3.5 Reproductive behaviour....................................................................................... 12
2.4 Ecology of thrips ....................................................................................................... 13
2.4.1 Ecology and diversity .......................................................................................... 13
2.4.2 Effects of climatic conditions on thrips population .............................................. 13
2.5 Insecticide resistance ................................................................................................. 14
2.6 Economic importance of thrips .................................................................................. 15
2.6.1 Direct damage ..................................................................................................... 15
2.6.2 Virus transmission............................................................................................... 17
2.6.4 Thrips as pollinators ............................................................................................ 20
2.7 Management strategies for thrips and spread of TSWV.............................................. 21
2.7.1 Monitoring .......................................................................................................... 21
2.7.2 Cultural control ................................................................................................... 22
2.7.3 Biological control of thrips .................................................................................. 24
2.7.3.1 Parasitism and predation................................................................................... 24
2.7.4 Chemical control ................................................................................................. 24
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CHAPTER THREE............................................................................................................. 26
3.0 MATERIALS AND METHODS ............................................................................... 26
3.1 Study site................................................................................................................... 26
3.2 Sample collection ...................................................................................................... 27
3.2.1 Maceration of thrips for slide mounting ............................................................... 27
3.2.2 Slide mounting .................................................................................................... 28
3.2.3 Insect identification ............................................................................................. 28
3.3 Farmers’ knowledge of thrips and insecticide usage pattern ....................................... 29
3.4 Population trends of thrips ......................................................................................... 29
3.4.1 Trap performance in capturing thrips ................................................................... 29
3.4.3 Abundance of adult thrips on Vegetable crops ..................................................... 30
3.4.4 Abundance of Thrips palmi and associated thrips species .................................... 31
3.4.5 Within plant distribution of Thrips palmi ............................................................. 31
3.5 Meteorological Data .................................................................................................. 32
3.6 Statistical Analyses .................................................................................................... 32
CHAPTER FOUR............................................................................................................... 33
4.0 RESULTS ................................................................................................................. 33
4.1 Plant survey for associated thrips species ................................................................... 33
4.2 Species composition of thrips..................................................................................... 33
4.3 Insect identification ................................................................................................... 41
4.3.1 Thrips palmi Karny ............................................................................................. 41
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4.3.2 Thrips tabaci Lindeman....................................................................................... 42
4.3.3 Frankliniella schultzei Trybom............................................................................ 42
4.3.4 Megalurothrips sjostedti Trybom ........................................................................ 43
4.4 Farmers’ knowledge of thrips and insecticide usage pattern ....................................... 44
4.4.1 Farmers’ knowledge of thrips .............................................................................. 44
4.4.2 Insect pest control................................................................................................ 44
4.5 Population trends of thrips ......................................................................................... 47
4.5.1 Trap Performance in capturing thrips................................................................... 47
4.5.2 Abundance of adult thrips on Vegetable crops ..................................................... 49
4.5.3 Abundance of Thrips palmi and associated thrips species on vegetable crops ...... 49
4.5.4 Within plant distribution of Thrips palmi ............................................................. 51
4.6 Relationship between trap catches of thrips and weather factors................................. 52
CHAPTER FIVE ................................................................................................................ 55
5.0 DISCUSSION ........................................................................................................... 55
CHAPTER SIX................................................................................................................... 59
6.0 CONCLUSION AND RECOMMENDATIONS........................................................ 59
6.1 CONCLUSION ......................................................................................................... 59
6.2 RECOMENDATIONS .............................................................................................. 60
REFERENCES ................................................................................................................... 61
APPENDICES .................................................................................................................... 72
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LIST OF FIGURES
Figure 1. Diagram showing a generalized thrips lifecycle (Center for Invasive Species
Research, University of California Riverside)...........................................................................9
Figure 2. Yellow sticky traps used to monitor thrips in greenhouses and in fields
……………..............................................................................................................................22
Figure 3. Percentage response on farmers’ knowledge of insects other than thrips on crops
infesting crops assessed using survey questionnaire………………………………...………44
Figure 4. Percentage response on insecticides used by farmers against insect pests during
survey………………...............................................................................................................45
Figure 5. Mean (± S.E) number of thrips caught by different trap types in five different fields
from September 2014 to March 2015……………………………………………………..…47
Figure. 6 Mean (± S.E) number of thrips per trap captured in different localities September
2014 to March 2015……………….........................................................................................48
Figure 7. Mean (± S.E) number of thrips per trap captured in different months from
September 2014 to March 2015……………………………………………………………...48
Figure 8. Mean (± S.E) number of adult thrips per plant collected over six weeks February to
March 2015………………………...………………………………..……………………….50
Figure 9. Mean (± S.E) number of adult thrips species per plant collected over six weeks
February to March 2015……………………………..……………………………………….51
Figure 10. Factor Interaction comparison chart of mean number of T. palmi collected at
different levels of cucumber plants .........................................................................................52
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Figure 11. Effect of average weekly temperature on total weekly trap catches of thrips from a
vegetable crops  in some parts of Greater Accra ……………………………...……………..53
Figure 12. Effect of average weekly temperature on total weekly trap catches of thrips
collected from a vegetable farm  at East Legon in Greater Accra………...………………... 53
Figure 13 Effect of total weekly rainfall on total weekly trap catches of thrips from vegetable
crops in some parts of Greater Accra from September 2014 to March 2015
..................................................................................................................................................54
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LIST OF PLATES
Plate 1. Thrips direct damage on plants………………..……………………………………16
Plate 2. Fruit damage in tomato associated with thrips virus transmission to the tomato plant
………………………………………………………………………………………………..17
Plate 3. (a) Yellow sticky trap(b) Blue sticky trap and (c) Grease
container……………………………………………………….……………………………..30
Plate 4. (a)Adult Thrips palmi (b) Seven segmented antennae of an adult Thrips palmi (c)
Head of an adult Thrips palmi showing red-pigmented ocelli……………………….……....41
Plate5. (a) Adult Thrips tabaci, (b) Seven segmented antennae of an adult..........................42
Plate 6. (a) Adult Frankliniella schultzei(b) Antenna of an adult Frankliniella schultzeiwith
eight antennal segments ……………………………………………...………………………43
Plate 7. (a) Adult Megalurothrips sjostedti, (b) Head of adult Megalurothrips sjostedti
showing paler antennal segment III…………………………………………………………..43
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LIST OF TABLES
Table 1.Localities from which thrips …………………………………….……...……...…..26
Table 2. Plant species surveyed for associated adult thrips and estimated thrips population
across some localities in Greater Accra and Eastern Region from July 2014 to March
2015…………………………………………………………………………………………..34
Table 3.Thrips species identified from associated host plants across some localities in Greater
Accra and Eastern Region……………………….…………………………………..36
Table 4. Number of thrips species on permanent slide mounts identified from various
vegetable crops…………...…………………………………………………………………..38
Table 5.Number of thrips species on permanent slide mounts identified from various
ornamental plants………………………...……………………….………………………….40
Table 6. Commonly used pesticides and their active ingredients…………………..………..46
Table 7. Mean (± S.E) number of thrips per vegetable crop across various localities surveyed
…………………………..……………………………………………………………………50
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LIST OF ABBREVIATIONS
ARPPIS African Regional Postgraduate Programme in Insect Science
CABI Centre for Agriculture and Biosciences International
CPPC Caribbean Plant Protection Commission
EC European Commission
EPPO European and Mediterranean Plant Protection Organization
EU European Union
EUROPHYTE European Union Notification System for Plant Health
FVO Food and Veterinary Office
NPPO National Plant Protection Organization
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LIST OF APPENDICES
Appendix 1. Survey Questionnaire……………………………………..……………………72
Appendix 2.Analysis of Variance for trap performance in catching thrips ……………...….75
Appendix 3. Analysis of Variance for effect of study locality on mean trap catches……....75
Appendix 4.Analysis of Variance for effect of sampling month on mean trap catches….....75
Appendix 5. Analysis of Variance for number of thrips and associated plant species…..…75
Appendix 6.Analysis of Variance for abundance of Thrips palmi on host plants……….…76
Appendix 7.Analysis of Variancetable for within plant distribution of T. palmi on cucumber
plants (two-factor with replication)…………………………………………….…………….76
Appendix 8.Tukey’s Honestly Significant Difference for within plant distribution of T. palmi
on cucumber plants………………………………..……………………………………… …76
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CHAPTER ONE
1.0 INTRODUCTION
Thrips (Thysanoptera: Thripidae) are important crop pests that cause damage to a wide range
of crops such as fruits, vegetables and ornamentals. Much of the injury they cause is through
direct feeding or oviposition, but there are several species which also transmit plant viruses
that are harmful (Samler, 2012).
Thrips are relatively small insects, ranging from 0.5 to 2 mm long. Other common names
include thunder flies, thunder bugs, thunder blights, storm flies, storm bugs, corn flies and
corn lice (www.amentsoc.org/insects/fact-files/orders/thysanoptera.html, accessed on 31
March 2015).They are mainly plant-feeders and many crops especially fruit and vegetable
crops are susceptible to thrips infestation (Palmer, 1990). Thrips occupy a wide variety of
ecological niches and so several species may be present on a single plant (Palmer, 1990).
Egg plants (Solanum melongena), pepper (Capsicum annuum), okra (Abelmoscus
esculentum), sweet pepper (Capsicum annuum var.), cucumber (Cucumis sativus),
Amaranthus species and onion plants (Allium cepa) are a few of the vegetable crops in Ghana
which are affected by thrips. Thrips are widely distributed in Southern Ghana and are found
in the Savannah and forest ecosystems (Banfo, 2009). These pest populations would build up
rapidly on host plants if not treated and would cause; injury to the plants, delayed maturity,
stunted growth, and yield loss (Samler, 2012). Thrips prefer rapidly growing-plant tissues and
as a result, fruit buds are damaged, leaving scars on the flowers. Scars can also be left on
fruits such as citrus and avocados, reducing their marketability and consumption.
Recently, many African countries have developed large production programmes for fruits and
vegetables in order to export to the European Union (EU) markets (Singh, 2002). In 1994,
Africa for example supplied about 92% of EU imports of green beans, with Kenya
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contributing 29% of total supply (Singh, 2002). Kenya’s success in the production and
marketing of fruits and vegetables could be because it is an equatorial country alongside
agro-climatic conditions which allow for year round crop production (McCulloch and Ota,
2002). Ghana, like Kenya, is an equatorial country that relies on small-scale farmers for
agricultural production with the climatic conditions and farm structures being similar to the
situation in Kenya. Many African and other developed countries are entering the export
market with fruit and vegetable crops, thus intensifying competition (Singh, 2002).
Despite the remarkable returns from  fruit and vegetable production worldwide, including
Ghana, the activity is constrained among other factors by viral diseases such as watermelon
mosaic viruses, tomato spotted wilt virus, bud necrosis virus (Capinera, 2000), nematodes,
declining soil fertility (Obeng-Ofori and Ankra, 2002) and insect pests such as aphids,
whiteflies, fruit flies, mealybugs, Diamondback moth and thrips among others, particularly
the  melon thrips, Thrips palmi Karny (Thysanoptera: Thripidae) which is an international
quarantine pest necessitating the use of high rates of pesticides and artificial fertilizers.
Thrips have been reported in many African countries including Ghana (Funderburk et al.,
2007). However, although Thrips palmi has been reported in Ivory Coast, Mauritius, Nigeria,
Reunion and Sudan, there are no records in Ghana (www.cabi.org/iscdatasheet/53745,
accessed on 2 January 2015).
Thrips are important quarantine pests of fruits and vegetables. Due to the small size of the
pest, detection in the field is difficult, so quarantine procedures are difficult to manage the
pest. Continued and increasing number of interceptions by European Union (EU) member
States in consignments of fruits and vegetables originating from Ghana due to the presence of
harmful organisms of concern to the EU led to a drop in Ghana’s export of these commodities
(Final Report of an Audit carried out in Ghana by FVO, 2012). In mid-July 2014, the
European Commission (EC) sent a warning letter to the National Plant Protection
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Organisations (NPPOs) in eight countries, warning that strict action against the import of fruit
and other products from specific countries would be taken if they fail to improve compliance
with phytosanitary regulations (Http://www.freshplaza.com/article/124021/EU-warns-fruit-
exporting-countries, accessed on 30th January 2015). Four of the countries notified include;
Ghana (pumpkins and aubergines), Dominican Republic (squashes, eggplant and mango),
Kenya (pumpkin, mango and basil) and Uganda (paprika). In July 2014, the EU imposed a
temporary ban on Ghanaian vegetable imports after consignments were identified as not
meeting quality standards (Http: //www.freshfruitportal.com/2014/07/31/eu-closes-door-on-
ghanaian-vegetables-imports, accessed on 31 March 2015). In 2013, Ghana received 181
interceptions due to detection of harmful organisms in vegetable consignments and thrips
accounted for 135 of the interceptions (Europhyte 2013 Food and Veterinary Office Annual
Report, 2014).
1.1 Justification
Thrips are serious pests of crops, yet little is known about their species composition and
population trends, especially of Thrips palmi, a quarantine pest, in Ghana. This lack of
information and the frequent interceptions of Ghanaian vegetable crops on account of Thrips
by the EU member states necessitated this study (Final Report of an Audit carried out in
Ghana by FVO, 2012).There is absence of adequate and convenient methods for assessing
population trends of thrips. Farmers depend mostly on excessive use of pesticides which
often leads to high pesticide residues in fruits and vegetables as well as increased cost of
production. Although the use of pesticide application has contributed tremendously in
ensuring regular supply of fresh vegetables to urban markets in Ghana, this has happened at a
high cost, as the health implications of the excessive use of pesticides have been enormous.
Therefore, it is important to monitor and record the different thrips species found in Ghana.
The study also examined the population dynamics of thrips in an effort to gather important
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information for both growers and researchers that could be used to improve thrips
management programmes.
1.2 Research Objectives
1.2.1 Main Objective
The main objective of this study was to determine the species composition of thrips and their
host range in Ghana.
1.2.2 Specific Objectives
The specific objectives were to;
1. Identify thrips species and their corresponding horticultural and ornamental host
plants in some selected parts of Greater Accra and Eastern Regions.
2. Assess farmers knowledge of thrips and management practices employed against
them.
3. Compare the suitability of two sticky traps in monitoring thrips populations
andestablish the possible presence of the invasive species, Thrips palmi in Ghana.
4. Determine the population trends of these insects in these parts of Ghana and establish
a relationship between trap catches and weather factors (temperature and rainfall).
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CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 Origin and Taxonomy of Thrips
De Geer in 1744 (Physapus), first described these insects and Linneaus later placed the
species known at the time, in a genus called Thrips, and in 1836, Haliday ranked these insects
to the Thysanoptera order. Thysanoptera are distributed worldwide predominating in tropical,
subtropical, and temperate regions (Lewis, 1997; 1973).
From the order Thysanoptera, more than 5000 species from two suborders: Terebrantia and
Tubulifera and in nine families: Merothripidae, Aeolothripidae, Heterothripidae,
Adiheterothripidae, Thripidae, Uzelothripidae, Fauriellidae, and Phlaeothripidae, are recorded
(Mound, 1997). About 93% of Thrips species belong to the families Thripidae and
Phlaeothripidae (Mound, 1997). Over 2000 species make up the family Thripidae in two
hundred and ninety genera recorded globally (Mound and Morris, 2007). These species are
grouped into four subfamilies, including; Panchaetothripinae, Dendrothripinae,
Sericothripinae and Thripinae with 125/35, 95/13, 140/3 and 1700/225 species/genera,
respectively (Mirab-balou and Xue-xin, 2011). The following eight genus-groups are
currently used: Anaphothrips, Frankliniella, Thrips, Megalurothrips, Taeniothrips,
Mycterothrips, Scirtothrips and Trichromothrips genus-groups (Mound and Palmer, 1981;
Mound and Masumoto, 2009). Most thrips of the family Thripidae associate mainly with
living plants and so, majority of thrips pests fall within this family (Kambiz, 2014).  There
are several genera each with at least a few species regarded as pests of various crops
worldwide. Some of such genera include; Anaphothrips Uzel, 1895, Aptinothrips Haliday,
1836, Caliothrips Daniel, 1904, Chirothrips Haliday, 1836, Dendrothrips Uzel, 1895,
Limothrips Haliday, 1836, Scirtothrips Shull, 1909 (Moritz et al.,2009; 2004).
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2.1.1 Thrips species
Some major species of thrips attacking crops in Africa include: African bean flower thrips
(Megalurothrips sjostedti), Thrips tabaci, Selenothrips rubrocintus, Frankliniella
schultzei,Retithrips syriacus, Tubufera sppand Liothrips spp (Banfor, 2009), Coffee thrips
(Diarthrothrips coffeae), Black tea thrips (Heliothrips haemorrhoidales), Banana thrips
(Hercinothrips bicinctus), Citrus thrips (Scirtothrips aurantii), Cacao or red banded thrips
(Selenothrips rubrocinctus), Tomato thrips (Ceratothripoides brunneus), Cereal thrips
(Haplothrips spp), Tea thrips (Scirtothrips kenyensis), the Western flower thrips
(Frankliniella occidentalis) (http://www.infonet-biovision.org/thrips, accessed on
29/09/2014) and Thrips palmi.
2.2 Biology of thrips
2.2.1 General biology
Most thrips attacking plants have a simple life history that varies but little fundamentally in
the different species (Bailey, 1938). After a few days the delicate, soft-bodied larvae hatch
and immediately begin feeding gregariously. The length of all the stages varies, of course,
with the temperature. Under favorable conditions the larvae attain full growth in 7 to 10 days,
when feeding ceases and the larvae either drop to the ground or rest quietly on the host. Some
mature larvae such as the pear thrips make an earthen cell in. the soil, in which they
transform. During this period the wings and other organs develop, and in 4 to 14 days, the
adult stage is reached (Bailey, 1938). During the growing season and the warmer parts of the
year the generations more or less overlap. The greatest seasonal abundance depends on the
requirements of the particular species. Ordinarily, however, thrips are most numerous during
the warmer and drier seasons; being small and rather delicate, they are destroyed by severe
weather conditions.
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2.2.2 Life cycle of thrips
Thrips undergo gradual metamorphosis. A generally, female thrips deposit eggs in slits made
in the leaf tissue by their sharp ovipositors. Each female lays 25 to 50 eggs which hatch (in
two to seven days) into active nymphs. Immature thrips resemble adults, but the immature
lack wings and are lightly coloured. There are two nymphal stages followed by two resting
stages: the prepupa and pupa. The resting stages can be found either on the host or in the soil
below the host. Under favourable conditions, the developmental period from egg to adult
ranges from 11 days to three weeks depending on the species, hence, a population may
increase quite rapidly. Parthenogenesis occurs in many species. Eggs take from 3 to 16 days
to hatch according to the species and conditions.
2.2.2.1 Eggs
Thrips lay very tiny egg, with each egg measuring about 0.25 mm long and 0.1 mm wide.
They appear whitish when freshly laid and turn pale yellow toward maturation. Eggs are
usually laid singly inside the plant tissue, and are therefore not visible. However, some thrips,
for example Haplothrips spp, lay eggs singly or in clusters attached to the plant surface
(http://www.infonet- biovision.org/thrips, accessed on 29/09/2014).
2.2.2.2 Larvae
The metamorphosis of thrips is somewhat intermediate between incomplete and complete.
The first two instars are called larvae. The first and second instar larvae are very small (0.5 to
1.2 mm), elongated, slender, and vary in colour from pale-yellow, orange or red according to
the species. They have piercing-sucking mouthparts. They resemble a miniature version of
the adults but do not have wings.
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2.2.2.3 Pre-pupae and pupae
In the suborder Terebrantia, the first two instars are followed by the third and fourth instars
which are inactive, do not feed, and have external wing pads. The third instar is called a
prepupa and the fourth the pupa, and are often spent on the ground in soil or litter. In the
suborder Tubulifera, the third and fourth instars are prepupae and the fifth pupa. They possess
short wing buds but lack functional wings. During these stages, thrips are inactive and do not
feed and therefore they do not do cause any damage to the plants. Pupation may occur on a
plant or in the soil beneath, depending on species (http://www.infonet-biovision.org/thrips,
accessed on 29/09/2014).
2.2.2.4 Adults
Adult thrips are tiny, measuring approximately 1 to 1.5 mm long, slender and usually winged.
The wings are long, narrow and fringed with long hairs, and at rest, are tied on the back along
the body. Their colour varies according to the species. Most species are black, brown or
yellow.
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Figure 1:Diagram showing a generalized thrips lifecycle (Center for Invasive Species
Research, University of California Riverside).
2.3 Behaviour and habits
2.3.1 Dispersal behaviour
Thrips generally depend on two modes for dispersal; artificial and natural dispersal (Hector,
2006). Artificial dispersal is usually human-assisted and is facilitated by the increasing
international transportation of agricultural products. Thrips are easily transported in various
products including potted and cut flowers and several fruits and vegetables that are imported
and exported across borders. They are difficult to spot in a port inspection due to their small
size. The eggs of thrips are found inside plant tissues and signs left by the ovipositing female
are minimal (Hector, 2006). Secondly, natural dispersal is accomplished mostly by fight.
Flight is the major method of active dispersal; however, they can be aerially dispersed by
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drifting in wind currents for many miles. Just before flying, thrips of the macropterous forms
bend their abdomen and use setae located on abdominal tergites V to VIII to comb those
located on the wings with the objective of increase the surfacing area of the wings,
facilitating take-off (Ellington, 1980).
2.3.2 Feeding behaviour
The mouthparts of thrips are one of the identifying characters of the order Thysanoptera and
are located on the underside of the head, forming a mouth cone. This structure is formed by a
single mandible. Thrips use the mandible to feed by “punching” a hole in the external walls
of the tissue to be fed upon and then using the stylets to suck the liquids from inside the
tissues (Kirk, 1997). Thrips generally, feed on diverse plant tissues including leaves, flowers,
fruits, pollen and some fungal tissues such as spores and hyphae. Thrips display a similar
feeding behavior for all plant tissues. Once landed on an appropriate substrate on which they
want to feed, thrips start a process of probing on the tissues. They start using the legs and
antennae, walking in circles or forming “figure eight” on the tissue. Once they find a suitable
spot, thrips use their mandible to probe and open a small hole in the cell wall (Hector, 2006).
A small amount of liquid comes from this small puncture. Thrips test the liquid for the
correct nutrients compositions using their palps. If the tissues and nutrient composition are
adequate, they use their mandible and head to punch a bigger hole in the tissue and start
feeding. This causes nearby cells to collapse. If the damage occurs in the ovary in the flower,
these marks will become magnified during the fruit development and the scars become very
noticeable, reducing fruit quality (Kirk, 1997a; Liburd et al., 2006).
2.3.2.1 Pollen-feeding
Pollen-feeding is also observed in thrips, mainly among flower thrips that feed on individual
pollen grains. Depending on thrips species and instar, grain volume, and temperature (Kirk,
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1987), the time spent on each pollen grain varies and falls between 3 to 120 seconds. Thrips
can ingest pollen from the anthers or the grains found around the flowers and leaves. The
potential damage that flower thrips can cause on pollen quantity depends on the plant
production of pollen and thrips population present in the field. Extremely high population of
thrips and very low production of pollen may affect the availability of pollen grains for
fertilization (Hector, 2006). A single thrips could potentially destroy between 0.2-0.7percent
of the pollen in a flower per day, assuming that it feeds exclusively on pollen (Kirk, 1987). In
addition, thrips might destroy the anthers or the pollen on stigmas, which would affect
pollination. The damage caused by thrips on plant fertilization depends on many factors such
as timing, amount of pollen produced by the plant, amount of pollen destroyed by thrips,
effectiveness of pollinators and temperature (Kirk, 1987). In addition to interfering with
pollen availability and fertilization, thrips balance their diet by consuming other plant tissues
(Kirk, 1997).
2.3.3 Predation
Thrips show a feeding behavior known as predation. A few specialist predators among thrips
have some behavioral adaptations such as speed or color among others. The most common
preys are mites and eggs. Some of the most common species of predatory thrips are
Haplothrips kurdjumovi Karny, which feed on moth and mite eggs (Putnam, 1942),
Scolothrips sexamaculatus (Pergande), which feed on mites that form webs (Trichilo and
Leigh, 1986), and Trichinothrips breviceps Bagnall, which feed exclusively on psocids (Kirk,
1997). Some species of thrips feed on other thrips larvae. These include; Aeolothrips
intermedius Bagnall, which feeds on thrips immature through their abdomen (Kirk 1997a).
Some of the polyphagous thrips are well known as pests. However, they can switch from
being pests to become predators. For example, Frankliniella occidentalis (Pergande) feed on
mites in cotton (Trichilo and Leigh, 1986) and prey on two spotted spider mites.
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2.3.4 Migration
Migration is not pronounced. The adults move about very little when sufficient food is
available. Thrips species are generally weak fliers. Local migrations, such as occur in the
pear thrips and the western flower thrips, are usually occasioned by a shortage of food or by
the discovering of a more desirable supply (Bailey, 1938). In such events, the migration is for
only a few hundred yards, generally in the direction of the prevailing wind.
Thrips are found on the most tender, succulent portions of the host plants; usually in buds, in
blossoms, under bracts, in leaf sheaths, or on bulbs. Usually the host range of thrips is very
wide, though some species, such as the gladiolus thrips, exhibit a narrower choice than
others. This cosmopolitan host range and the habit of living somewhat concealed make
control difficult and eradication almost impossible. Heavy rains and cold weather are most
important factors that affect natural control of thrips (Bailey, 1938).
2.3.5 Reproductive behaviour
Factors such as plant species and quality (age, vigor, phenological stage) affect the net
reproductive rate of thrips populations. Abiotic conditions affect the reproduction of thrips as
well. These include light regimen, temperature, and humidity (Kirk, 1997b). There are
relationships among thrips from the same or from different species and these can be
understood through some intrinsic behaviour displayed. The first one is the use of
semiochemicals such as alarm pheromones, aggregation pheromones, and defensive
mechanisms, (Terry, 1997). Males of F. occidentalis produce some type of substance with an
attractive effect on females of the same species (Kirk and Hamilton, 2004). The females of
Terebrantian species raise the tip of their abdomen during oviposition, test the plant tissues
using the setae in the last abdominal segment, and insert the ovipositor into plant tissues
(Hector, 2006). While in this position; the saw-like ovipositor cuts a space for the egg in the
tissue, which is pushed out by a contraction of the abdomen. Thrips prefer to lay their eggs in
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mature non-expanding tissues to avoid having the eggs crushed by the expanding cells (Terry,
1997). Oviposition preferences depend on the species. Most species prefer to oviposit on
leaves or on floral tissues. In citrus, F. bispinosa oviposit in the floral tissues, it has a
preference for the pistil- calyx area followed by the petals and finally, filaments and anthers
(Childers and Anchor, 1991). Other thrips species lay their eggs close to the inner veins of the
leaves or in the fruits. The place and plant stage determines the damage caused by these
thrips due to oviposition. Thrips that lay their eggs and feed in the commercial part of the
plant, flower or fruits, are considered as major pests of agricultural sector (Hector, 2006).
2.4 Ecology of thrips
2.4.1 Ecology and diversity
In Thysanoptera, Tubulifera has one family and Terebrantia eight families distributed
worldwide (Moritz et al., 2004b). The females in Tubulifera do not have an ovipositor and
the distal abdominal segment is similar to the males. This segment is tubular in shape and
ends in a series of setae. The forewings in Tubulifera have neither venation nor setae except
for the base. Terebrantia are the most common suborder and the one that has the greatest
effect on agriculture. Close to 94% of the total pest species are in this suborder, all of them in
the family Thripidae (Moritz et al., 2004b).
2.4.2 Effects of climatic conditions on thrips population
The influence of weather on the activity and rate of multiplication of insects and the natural
growth of population determines the total variability in thrips populations in crops (Kirk,
1997). Understanding the effects of weather on thrips population dynamics is essential in
predicting thrips population. Weather variables such as rainfall, temperature, relative
humidity and wind have significant effects on thrips numbers (Kirk, 1997). Relatively high
temperatures and lack of rainfall have been associated with increase in onion thrips
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population, while high relative humidity and rainfall reduce thrips population (Hamdy and
Salem, 1994). Temperature and relative humidity also influence the intrinsic rate of natural
increase of the thrips (Murai, 2000). A basic understanding of the relationship of these factors
with thrips population aids in developing an integrated management strategy for thrips in
crops and in determining the potential pest management needs for a given climatic trend
(Waiganjo et al., 2008).
2.5 Insecticide resistance
In an attempt to protect vegetable crops from high pressure from insect pests, farmers rely
mainly on indiscriminate and widespread use of synthetic insecticides in vegetable cultivation
and this has led to insecticide resistance development in the insect pests (Odhiambo et al.,
2010).With insect populations developing resistance to insecticides, the probability of losing
most of the beneficial insects including pollinators and natural enemies is extremely high due
to increase in dosage and frequency of insecticide application (Owusu, 1997). Lack of
adequate knowledge on appropriateness of insecticides, application time and dosage has
resulted in decreased yields and undesirable chemical residues in produce.
The development of resistance to insecticides is of paramount concern with thrips (Sparks et
al., 2001). The potential for resistance is high because there is generally a single mode of
action or chemistry that is effective for each pest species, and because female thrips
reproduce without mating (parthenogenetic reproduction). Thus, thrips that survive an
insecticide application produce individuals that can survive exposure to the same type of
insecticide. The location of thrips on onion plants and other plants also affects the efficacy of
insecticides and the development of resistance. In the neck and leaf folds, thrips are
somewhat protected from insecticide exposure. This reduces the effectiveness of the
treatment, but may also ensure that some susceptible individuals remain within the population
(Sparks et al., 2001). Resistance has not only developed against insecticides targeting western
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flower thrips, but also insecticides used to treat other pest species. Correspondingly, a number
of different resistance mechanisms have been characterized to date, including metabolic
detoxification, reduced penetration, altered target site resistance, and knockdown resistance
(Bielza, 2008). Behaviour and ecology of thrips can minimize exposure to insecticides and
they are well suited to evolve resistance to multiple classes of insecticides.  There have been
incidences of resistance reported to all major classes of insecticides from all regions of the
world (Bielza et al., 2007b; Kay and Herron, 2010; Weiss et al., 2009) since the first reported
case of control failures with insecticides (toxaphene, an organochlorine). Despite early
reports regarding difficulties with pyrethroids, they have continued to be used against western
flower thrips extensively, with the same outcome of resistance development
(Thalavaisundaram et al., 2008).
2.6 Economic importance of thrips
2.6.1 Direct damage
Many thrips are destructive pests of plants, especially grain crops, fruits and vegetables, and
ornamentals. Feeding activities result in plant deformities, scarring, loss of yield, and in
some cases, transmission of plant pathogens. Predatory thrips are however beneficial in that
they may control mites and other small insects that are pests. Most thrips considered as severe
pests are polyphagous. Due to their high adaptability, thrips can feed on various resources
and modify their larval stages, adapting to various environmental conditions. Thrips are
notorious in moving their population to alternate hosts during the season when the main hosts
are not very favourable. For example; the flower thrips, which reproduce and feed in the
flowers of crops and in the absence of flowers, they migrate to nearby crops and wild flowers
to continue their cycle (Kirk, 1997b). Thrips pierce plant cells with their mouthparts and feed
on the plant cell sap, leading to the collapse of plant cells. This results in deformed flowers,
leaves, stems, shoots and fruit. Silvery flecked scars or small black fecal spots also develop
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on the leaves and fruits (Plates 1). Thrips also damage buds and flowers through their egg
laying and this often leads to deformed fruits being formed (Sonya et al., 2004).
a b
c d
Pate 1:Direct damage: a)Scarring on garden egg fruit, b)Silvering damage to a cucumber
leaf(L. Zhang and H. Brown, Diagnostic Services, Darwin, 2008), c) Thrips and damage on
onion leaves (Whitney Cranshaw, Colorado State University, Bugwood.org) and d)Feeding
damage on sweet pepper plant.
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2.6.2 Virus transmission
2.6.2.1 Tomato spotted wilt virus (TSWV)
In addition to causing direct damage to crops, thrips also spread plant viruses. For example,
the Western Flower Thrips (WFT), onion thrips, and tomato thrips spread the TSWV. Plate 2
shows a typical example of fruit damage in tomato associated with thrips virus transmission
to the tomato plant. The concentric ring pattern is indicative of TSWV. This damage can
show up many weeks after virus transmission occurred. TSWV was first found in Western
Australia in the 1920s, causing sporadic epidemics in vegetable and ornamental crops (Sonya
et al., 2004). The efficiency with which the virus is transmitted differs between species: WFT
is the most efficient vector of TSWV. TSWV affects mainly tomatoes, capsicum, and lettuce
where it can cause up to 100 per cent crop loss. Plants such as grapes, stone, pome fruit,
strawberry, brassica, and cucumber are not affected by the virus (Sonya et al., 2004). Plants
infected with TSWV show one or more of the following symptoms: irregular necrotic (dead)
spots on leaves, black or purple stem streaks, chlorosis (yellowing), chlorotic blotching,
chlorotic or necrotic ring spots and line patterns on leaves and fruit, leaf distortion and
deformation, dropping of leaves or shedding of buds, dieback and leaf collapse, stripes on
petals and plant death caused by wilting (Sonya et al., 2004).
ab
Plate 2:a)TSWV symptom/ damage to susceptible tomato fruit b) Dimpling of tomato fruit
surface caused by thrips feeding. (Authors: D. Riley, R. Srinivasan, S. V. Joseph, and S.
Diffie).
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2.6.2.2 Tospovirus
Tospovirus is one of the most damaging groups of pathogens in agriculture. Recently, the
spread of infected plants and vectors has increased due to the increase in international trade,
worldwide (Hector, 2006). Thrips and viruses are probably two of the most difficult things to
detect in the ports of entry. Thrips eggs inside the plant tissues infected with the viruses are
virtually impossible to detect (Lathman and Jones, 1997). There are 16 species of viruses in
the genus Tospovirus, family: Bunyaviridae, recognized as plant pests, and they are
transmitted by 11 species of thrips, of the family Thripidae (Ullman, 2005).
Thrips acquire viruses in the first or early second instar when there is a close connection
between mid-gut, visceral muscles and salivary glands (Moritz et al., 2004a). Once the wing
muscles start developing and the supra-oesophageal ganglion moves towards the head the
connection between the salivary glands, the mid-gut, and the visceral muscles is ended
stopping the movement of virus particles into the salivary glands. If the thrips did not acquire
the virus during this short period, it will not be able to acquire the virus due to the lack of this
connection. In adult thrips, the virus is located in the malpighian tubes, in the lumen, the
hemocoel, and in the salivary glands. Until recently, the only proven way thrips transmit the
virus is through the salivary glands during feeding. However, there is enough evidence to
support the possibility that the virus might be transmitted through excrements and oviposition
wounds (Moritz et al., 2004a).
2.6.3.0 Thrips as quarantine pests
Thrips pose a phytosanitary risk to agricultural crops in international trade. Thrips palmi for
example is an A1 quarantine pest for European Plant Protection Organization (OEPP/EPPO,
1989) and an A2 pest for The Caribbean Plant Protection Commission (CPPC).  In the EPPO
region, T. palmi presents a serious threat to a wide variety of crops grown under glass. It
could possibly establish on field crops in southern areas of the EPPO region, as has happened
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for Frankliniella occidentalis (EPPO/CABI, 1996a) which was originally considered to
present a risk only under glass. Thrips palmi is not apparently a vector of TSWV
(EPPO/CABI, 1996b) but it does vector closely related viruses in Japan and Taiwan.
2.6.3.1 Thrips palmi
Thrips palmi is a polyphagous pest of much economic importance (Kirk 1997). It has a wide
host range that includes at least 50 different plant species (Wang and Chu 1986). Damage
caused by T. palmi is primarily due to feeding by adults and immature on leaves and fruits of
its host plant. Feeding may result in damaged terminals of the host, bronzing of leaves, which
at the time of severe infestation may completely dry and die off, as well as production of
scarred and deformed fruits. T. palmi may also cause host damage by transmitting at least 6
of the known tospoviruses (Nagata et al., 2002). Worldwide serious infestation of T. palmi
has been detected on plants from family Solanaceae (eggplants, pepper, and potato),
Cucurbitaceae (cucumber, watermelon, cantaloupe, and squash), and Leguminosae (kidney
bean, snap bean, broad bean, cowpea, soybean, and white clover) (Talekar 1991; Nakahara,
1984). T. palmi is native to Southeast Asia, specifically at Java (Indonesia) where it was
reported by Karny (1925) as a pest of tobacco.
2.6.3.2 Distribution of Thrips palmi
Its distribution was limited to Southeast Asia until the mid-1970s (Capinera, 2008) when a
serious outbreak occurred in southern Japan (Sakimura et al., 1986). Subsequently, it became
established in most of the Asian countries; Bangladesh, Brunei Darussalam, China, Hong
Kong, India, Japan, Malaysia, Myanmar, Pakistan, Philippines, Singapore, Sri Lanka, Taiwan
and Thailand. Currently, T. palmi has a wide distribution around the globe and it occurs in
almost all the habitable landmarks of the world: Australia, Guam, New Caledonia, Samoa,
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Wallis and Futuna (Oceania); Netherland (Europe); Mauritius, Nigeria, Reunion, and Sudan
(Africa); Brazil, Guyana, and Venezuela (South America); Antigua and Barbuda, Barbados,
Dominica, Dominican Republic, Grenada, Guadeloupe, Haiti, Martinique, Puerto Rico, St.
Lucia, St. Kits and Nevis, Trinidad and Tobago (Central America and Caribbean); Hawaii
and Florida (North America) (CABI, 1998).
2.6.4 Thrips as pollinators
Thrips pollinate numerous plant species, either alone or in conjunction with other vectors
(animals, wind). An adult thrips can transport up to several hundred pollen grains. They can
move within a plant, between neighbouring plants, or even be transported on the wind to
distant conspecific plants. Some species are highly specific to particular host blossoms
(thrips.info/wiki/Thrips_and_pollination, accessed on 30/09/2014). Wind-pollination is
commonly confused with thrips-pollination because netting rarely can exclude these insects,
and plant breeders relying on hand pollination for specific crosses sometimes obtain unusual
results due to pollen carried by thrips. Some thrips species are known only from particular
hosts but the degree of thrips host specificity is often uncertain due to lack of detailed
observations (Mound, 2013). Female and male thrips visit male blossoms at anthesis cued by
scent, colour and possibly form. They feed on pollen and mate. Gravid females primarily
oviposit here or on other male anthesis (period during which a flower is fully open and
functional) blossoms but can also move to preanthesis male blossoms for oviposition. Rapid
build-up of thrips populations can occur on male blossoms alone or on sterile (but usually
nutritive) preanthesis male blossom appendages, prior to female blossom anthesis
(thrips.info/wiki/Thrips_and_pollination, 30/09/2014).Certainly with so many species of
Thysanoptera known to utilize pollen, the potential for thrips to effect pollination is possible.
However, thrips have been systematically overlooked by pollination biologists. These small
insects have generally been considered only a minor or secondary contributor to pollination
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of some plants, many of which are crops. This attitude is partly due to thrips lacking a
number of characters that are deemed essential to be an efficient pollinator (Kirk, 1997a).
Such characters include; thrips are tiny and have no specific organs or structures that carry
pollen; they carry only a small number of pollen grains per individual; and they are assumed
to be poor fliers with little directed flight, and rarely leave their flowers. However, these traits
are not always true for thrips, nor are these traits always limitations. Thrips do have some
directed flight, and some species do move between flowers very often. Members of both
Frankliniella and Thrips genera are considered important pollinators of some crops. Even
though individual thrips only carry a few grains, sometimes up to hundreds of grains (Kirk,
1997a), they can move between plants and flowers in high numbers.
2.7 Management strategies for thrips and spread of TSWV
2.7.1 Monitoring
Monitoring to identify when thrips arrive and to determine population levels is helpful in
designing an appropriate control strategy. The numbers present can be used to determine
action thresholds for applying pesticides. When considering appropriate action threshold
levels, it is important to remember that no single number will always be a reliable guide.
Climate is a factor to consider in designing control strategies. Hot and dry conditions favor
thrips damage, and cool rainy weather hinders their damage. In drier years, fewer thrips per
leaf can be tolerated before yield losses result (Fournier et al., 1995). In onions, thrips must
be controlled before the crop reaches the early bulbing stage, so that populations do not
exceed manageable levels (Coviello et al., 1993). Sticky traps (figure 2) could be placed in
the empty greenhouse to attract many of the remaining adult thrips. It is important that the
greenhouse contains no plant material for this strategy to work.
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Figure 2: Yellow sticky traps used to monitor thrips in greenhouses and in fields. (Sonya et
al., 2004)
2.7.2 Cultural control
2.7.2.1 Farm sanitation
Weed destruction in the field and surrounding margins can help to reduce thrips populations,
since these areas serve as overwintering and re-infestation sites. Drought stress increases the
susceptibility of onions to thrips damage. Adequate irrigation throughout the growing season
is a critical factor in minimizing damage (Fournier et al., 1995). Thrips are particularly
attracted to flowering weeds as they feed on the pollen. Thrips feed on and reproduce in
weeds, particularly if there are no cultivated crops being grown. When a new crop is planted
the thrips move off the weeds and onto the new crop. Weed-free areas of at least 10 m around
the crop are necessary. This can be bare ground, closely mown grass, concrete, stones, or
some other hard surface. Care should be taken when spraying weeds with herbicides because
as the weeds die off, thrips can move off the weeds onto crop (Sonya et al., 2004). Weeds act
as reservoirs for TSWV and thrips. Plants infected with TSWV should be removed when the
first symptoms of the disease are seen. Dispose of plants by burning or burying (Sonya et al.,
2004). The plants may be sprayed with insecticide first, to ensure that any thrips infected with
TSWV are killed. Seeds do not habour TSWV; hence, it is advisable to grow plants from
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seeds where possible. However, if buying seedlings check with suppliers to ascertain that
they monitor for thrips.
2.7.2.2 Soil fertility
Soil fertility management may also affect thrips infestation and damage. Lack of adequate
soil calcium may invite higher populations of thrips (Rateaver and Gylver, 1993). Nutritional
balance can reduce thrips attack. High nitrate levels will invite thrips, and the effects of
excessive nitrate are compounded by shortages of potassium, sulfur, boron, and manganese.
Foliar applications of soluble calcium will balance the excess nitrogen (Cantisano, 1999).
2.7.2.3 Thrips proof mesh
Thrips in confined environments such as glass or screen houses can be prevented by barriers
of fine mesh which help to prevent thrips’ movement. However, this mesh is expensive and
since there is need to cover all vents and doorways, air circulation is reduced and extra
venting may be required. Trials have indicated that the maximum hole size for the exclusion
of WFT is 0.192 mm (Sonya et al., 2004).
2.7.2.4 Greenhouse sterilization
Greenhouses should be sterilized between crop plantings. This could be done by steaming the
soil to kill pupae and by fumigating the greenhouse to kill adults (Sonya et al., 2004).
Alternatively, keep the greenhouse hot, dry, and empty for at least one week, or longer in
cold weather. Any thrips in egg or pupal stages will hatch and subsequently die.
2.7.2.5 Plant quarantine
The spread of thrips and TSWV mostly takes place through the movement of plant materials
(Sonya et al., 2004). So, it is good to inspect incoming plant material thoroughly for thrips.
Plants are held in a monitored quarantine area if possible for up to two weeks. This allows
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enough time for all eggs to hatch and pupae to emerge. Quarantining plants ensures that they
are not infected with TSWV. A quarantine area may be a glasshouse used specifically for that
purpose, or a sectioned-off holding area. This can be made using a double thickness of shade
cloth treated with permethrin.
2.7.3 Biological control of thrips
2.7.3.1 Parasitism and predation
A number of beneficial organisms work to suppress thrips. These include ladybird beetles,
minute pirate bugs, ground beetles, big-eyed bugs, lacewings, hover flies, predatory mites,
and spiders (Hoffmann et al., 1996). However, these predators and parasites may be
hampered by the fact that thrips feed under close-fitting leaves and down in the leaf sheaths
where they are difficult for predators to find. Insecticides, even those cleared for use in
organic production; also tend to work against beneficial predators and parasites. They should
therefore be used minimally and applied with caution (Kuepper, 2004). Occasionally, thrips
populations may explode, as large numbers migrate from nearby vegetation. In such
circumstances, in-field populations of beneficial predators and parasites may not be adequate.
The numbers of predatory and parasitic insects and arachnids can be increased on the farm by
providing protective habitats for them. These habitats; often called refugia, can be integrated
into crop rotation planning (Kuepper, 2004).Naturally occurring fungal diseases can also
devastate thrips populations (Hoffmann et al., 1996).
2.7.4 Chemical control
Thrips can be difficult to control effectively with insecticides, partly due to their mobility,
feeding behavior and protected egg and pupal stages (Bethke et al., 2014); hence, improper
timing of application of insecticides, failure to treat proper plant parts and inadequate spray
coverage when using contact insecticides, could be likely mistakes that can prevent
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potentially effective insecticides from actually providing the needed control (Bethke et al.,
2014). Therefore, taking action before the thrips become established, helps limit population
increase. It is also good to reserve the insecticides recommended for the control of thrips until
thrips is found in crops. Use small droplets (less than 100 microns) rather than large droplets,
as they are more effective. Droplet size can be checked using water-sensitive paper. The
leaves stay wet longer and prolong exposure of the thrips to the insecticide (Sonya et al.,
2004). Mixed insecticides may not be compatible and could cause phytotoxic effects to the
crop and be dangerous to human health. This would likely increase the level of resistance in
the thrips population, as thrips are being exposed to multiple insecticides, rather than just one.
Proper control of thrips should take place before flowering where possible because once
thrips enter the flowers; they are difficult to reach with insecticides as they are hidden. The
pH affects the activity of insecticides and so should be checked (Sonya et al., 2004). A
neutral pH is best (pH 6.5 to 7.0).
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CHAPTER THREE
3.0 MATERIALS AND METHODS
3.1 Study site
In this study, a survey of vegetable crops and ornamental plants was undertaken in some
vegetable growing areas and ornamental gardens in Greater Accra and Eastern Regions of
Ghana (Table 1).
Table 1: Localities from which thrips were collected
Region Locality
Eastern Region Akuapim-Mampong
Tutu-Akuapem
Ahwerase
Aburi Botanical Gardens
Greater Accra Ashaiman
Dzorwulu: North Dzorwulu and Ebony
Opebia (Kotoka International Airport area)
Haatso
Tema Harbour
East Legon
University of Ghana farm; Legon
Department of Animal Biology and Conservation Science,
University of Ghana, Legon
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Accra Metropolitan Area lies in the coastal Savannah zone of Ghana with a bimodal rainfall
pattern. It covers about 240 square kilometres with agricultural lands covering about 1,091
hectares (MoFA, 2013). The average annual rainfall records between 750 mm to 810 mm and
the mean monthly temperature ranges from 24.7oC to 28oC with an average of 26.8oC
(mofa.gov.gh/site/?page_id=1561,accessed on 15 February 2015). In Accra, there are about
800-1000 vegetable crop farmers of whom 60% and 40% produce exotic and indigenous or
traditional vegetable crops respectively (Obuobie et al., 2006). Major crops produced include
exotic vegetable (Lettuce, cabbage, cucumber, spring onion and cauliflower while the
traditional crops include; tomato, okro, garden eggs, onion, sweet and chilli pepper (Obuobie
et al., 2006).
3.2 Sample collection
A number of methods were employed in collecting thrips samples. Thrips were collected
from flowers, leaves and twigs of host plants by beating and jarring. Thrips that fell unto the
plastic tray placed under the host plants were picked off with a fine paint brush into the
collecting fluid, a mixture of 70% alcohol and 5% acetic acid in the ratio 4:1 in plastic vials.
Adult thrips were also collected from plants by taking samples of heavily infested leaves and
flowers. Plant parts found with thrips were also slowly lowered into plastic bottles containing
the collecting fluid and the cap applied. The plant parts were then shaken vigorously to
dislodge thrips from them. Dislodged thrips in alcohol were transported to the laboratory for
identification. Specimens stored in alcohol were kept in the dark to prevent loss of colour
before identification.
3.2.1 Maceration of thrips for slide mounting
Sample specimens from field storage bottles were placed in watch glasses and collecting fluid
replaced with fresh 60% alcohol and stored for 20 minutes and later replaced with 5%
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Potassium hydroxide (KOH). The insect abdomen was gently punctured behind the hind
coxae using micro- pins to allow rapid entry of the KOH (Palmer, 1990). When soft, the
specimens were gently massaged to expel the body contents. Potassium hydroxide was
washed off with 60% alcohol and stored for 15 to 25 minutes then replaced with Xylene and
left to stand for 5 to 10 minutes and then washed off with 60% alcohol. Acetic acid was then
introduced and allowed to stand for 5 to 10 minutes and then washed off with 60% alcohol.
Specimens were then passed through a series of alcohol concentrations starting from 65%,
followed by 75%, 85%, 90% and 95% ethanol to initiate gradual dehydration of the
specimens. Thrips were placed in each of the above mentioned alcohol concentrations for 5 to
8 minutes to avoid any moisture interactions at the final stage of slide mounting.
3.2.2 Slide mounting
The process of mounting was facilitated by preparing a small mounting block. A clean 16mm
diameter cover slide was placed on the mounting block and a drop of Canada balsam placed
onto the centre of the cover slip and into this position, a specimen was placed with ventral
side uppermost. The legs and wings were spread and the antennae straightened by pressing on
the basal segments with a fine needle. A clean microscope slide was inverted and lowered
firmly but gently onto the specimen. The preparations were allowed to stand untouched for
one day until the specimens were firmly held on the slides.
3.2.3 Insect identification
The specimens were identified using identification keys according to Palmer (1990). Thrips
were identified to species level. Identification was based on morphological features of the
thrips. For reference purposes, the specimen on the microscope slide was placed with the
head directed towards the determiner and on the right hand side, a label was placed indicating
the host plant of the thrips, country, locality, date and name of collector (Coll.). On the left
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hand side, a label was placed indicating the name of specimen, name of author and name of
the determiner (Det.).
3.3 Farmers’ knowledge of thrips and insecticide usage pattern
A total of 50 farms were visited and the purpose of the survey explained to the farmers and
35 of them responsible for management decisions of their farms who consented were
interviewed. Assessment was based on voluntary collaboration of the farmers. Each farm had
more than one type of crop cultivated and management was mainly by family labour. A
Questionnaire consisting of open and closed ended questions were designed and used to
obtain data through interviews with farmers in the farms and direct observation of farming
practices during interviews. The survey assessed farmers’ knowledge of thrips and other
insect pests, pest management practices, insecticide application pattern, storage and disposal
of empty insecticide containers, precautionary measures taken during insecticide application
and the source of farmers’ technical knowledge on pest management. The data obtained from
the survey were summarized using the Statistical Package for Social Science (SPSS) v20.0
and presented in tables, bar and pie charts.
3.4 Population trends of thrips
This study was aimed at evaluating and comparing the relative suitability of blue and yellow
sticky traps in determining the relative abundance of thrips on the various host plants
monitored.
3.4.1 Trap performance in capturing thrips
Plastic yellow plates measuring 25 cm by 20 cm (Plate 3a) were improvised. Blue cardboard
papers measuring 25 cm by 20 cm (Plate 3b) were also improvised and each piece of the
paper was inserted into a transparent poly bag. Grease (ABRO #3 super heavy-duty grease)
(Banfo 2009), an adhesive was applied on surfaces of both the yellow and blue boards (Plate
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3c). The sticky boards were then fastened to pieces of wood and pinned randomly in the field.
Length of the wood was adjusted by replacing with longer ones as the plants grew taller.
Each field had ten traps including five blue and five yellow traps placed 10 m apart. Traps
were re-randomized every two weeks to minimize effects due to position of traps.
Adult thrips were recorded weekly. Polybags from traps were removed and sent to the
laboratory and insects collected using fine paint brush (soaked in Xylene) into glass wells and
viewed under a light microscope and counted. Trap catches were recorded with respect to the
trap colour. At the same time, ten plants were randomly sampled. Leaves, flowers and stems
of these plants were inspected. Flower petals were opened and inner surfaces examined for
adult thrips. Adult thrips were counted with the aid of a magnifying hand lens.
a b c
Plate 3: (a) Yellow sticky trap(b) Blue sticky trap and (c) Grease container
3.4.3 Abundance of adult thrips on Vegetable crops
The abundance of thrips on plant species was studied on eggplant (Solanum melongena),
cucumber (Cucumis sativus), sweet pepper (Capsicum annuum var) and gboma (Solanum
macrocarpon), cabbage (Brassica oleracea var. capitata), Amaranthus creutusand lettuce
(Lactuca sativa) which are some of the commonly cultivated vegetables in southern Ghana.
Samples were collected from these crop canopies in commercial farms across the study area.
Ten flowers or leaves (a flower or leaf per plant) were collected from every plot for each
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plant species. Samples were placed in brown envelopes and transported to the laboratory,
dislodged in 70% ethanol, viewed under a microscope (OLYMPUS SZ61), counted and
recorded. Data on abundance of adult thrips on each crop were averaged for all samplings and
mean number of adults per crop compared using one way analysis of variance. Data was log-
transformed (log10 (x+1)).
3.4.4 Abundance of Thrips palmi and associated thrips species
Four plant species including; eggplant (Solanum melongena), cucumber (Cucumis sativus),
sweet pepper (Capsicum annuum var) and Gboma (Solanum macrocarpon)were examined in
a commercial vegetable farm at East Legonfrom January 2015 to March 2015. These plant
species were transplanted in early January 2015. Each crop was planted in a separate plot, but
both plots were close to each other. On each plot, ten leaves/flowers per plot depending on
the host plant (a leaf/flower per plant), were randomly collected. Samples were processed as
described above (section 3.43 above).Adult thrips were mounted on microscope slides for
further identification to species level.
3.4.5Within plant distribution of Thrips palmi
Thrips exhibit differential feeding preference for various parts of its host plants. Based on
thrips abundance on the plant species sampled, T. palmi was the only thrips species collected
on cucumber leaves; hence cucumber was used for this study. Cucumber was directly seeded
on a flat ground. The field was irrigated once a week. Sampling began three weeks after
planting. Within-plant distribution of T. palmi on cucumber was studied in a commercial field
at Haatso with field size of 0.16acres. On each sampling date, three plants were randomly
selected from the edges and middle point of the cucumber plot. Each plant was stratified into
three sections: a freshly emerged terminal leaf bud (2-5 days old), a middle leaf and a bottom
leaf (from the top). All samples were transported in brown envelopes to the African Regional
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Postgraduate Programme in Insect Science (ARPPIS) laboratory, University of Ghana, Legon
where samples were placed in a plastic bowl with 70% ethanol for about 30 minutes to
dislodge various life stages of thrips. Samples were carefully taken out of the cup leaving
thrips in ethanol. The plastic bowl with its content was then placed under light microscope to
record number of adult and larval thrips.
3.5 Meteorological Data
Data on average daily temperature and rainfall were collected from the Ghana Meteorological
Agency located at Mempasem in the Greater Accra Region. Average weekly temperatures
and total weekly rainfall were calculated from the raw data and used to study their
relationship with thrips population on sticky traps.
3.6 Statistical Analyses
Trap captured data for the 30 weeks of data collection were analyzed for the whole study
period. Data on trap catches, abundance of thrips and within plant distribution of thrips were
square root (√x) and log-transformed (log (x+1)), respectively. The general analysis of
variance was used to determine the effect of trap colour and variation in abundance and
distribution of thrips. Where analysis of variance (ANOVA) showed significant difference
among means of plant parts (treatment), the Tukey-Kramer honestly significant difference
(HSD) test was used to separate the means for the preferred plant parts.
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CHAPTER FOUR
4.0 RESULTS
4.1 Plant survey for associated thrips species
Various vegetable and ornamental plants as well as some tree crops and weeds randomly
surveyed were found to host thrips species (Table 2). Thrips were found in flowers, leaves
and fruits in all the fields surveyed. However, not all plant species contained thrips during the
survey. For instance, no thrips were found in Theobroma cacao (Cocoa plants), Citrus
sinensis (Orange plants) and Carica papaya (Paw-paw plants) (Table 2). More thrips were
collected from cowpea plants followed by Gboma and Onion plants (Table 4).
4.2 Species composition of thrips
Thrips palmi Karny, Megalurothrips sjostedti Trybom, Microcephalothrips abdominalis
Crawford, Frankliniella schultzei Trybom, Thrips tabaci Lindema, among other thrips
species were collected and identified from various host plants across localities during this
study (Table 3). F. schultzei, M. sjostedti and T. palmi were the most abundant thrips species
on vegetable crops in terms of number of identified thrips on slide mounts (Table 4). On
ornamental plants, M. sjostedti was the most abundant thrips species followed by Haplothrips
sp. Among ornamental plants surveyed, Thumbergia erecta and Rullia blumei hosted most of
the thrips followed by the Jasminium plant (Table 5).
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Table 2:Plant species surveyed for associated adult thrips and estimated thrips population
across some localities in Greater Accra and Eastern Region from July 2014 to March 2015.
Category Common name Scientific nameof plant Thrips Estimated
of plant status population
Vegetable Egg plant Solanum melongena Present **
Cowpea Vigna unguiculata Present **
Gboma Solanum macrocarpon Present **
Onion Allium cepa Present **
Tomato Solanum lycopersicum Present **
Pepper Capsicum annuum Present **
Sweet pepper Capsicum annuum var. Present **
Cucumber Cucumis sativus Present **
Amaranthus Amaranthus creutus Present **
Sorrel Hibiscus sabdariffa Present **
Lettuce Lactuca sativa Present **
Cabbage Brassica oleracea var. capitata Present **
Cauliflower Brassica oleracea var. botrytis Present **
Water melon Citrullus lanatus Present **
Leeks Allium ampeloprasum Present **
Spring Onion Allium fistulosum Present **
Okra Abelmoscus esculentum Present **
Ornamentals
King’s Mantle Thurmbergia erecta Present **
** = More than ten adult thrips collected per leaf/ flower of each plant species
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Table 2 cont’d:Plant species surveyed for associated adult thrips and estimated thrips
population across some localities in Greater Accra and Eastern Region from July 2014 to
March 2015.
Category Common name of Scientific name of plant Thrips Estimated
plant status population
Ornamentals Blue bell flower Rullia blumei Present **
Verbena Verbena sp Present **
Moss red rose Portulaca grandiflora Present **
Turkeyberry Solanum torvum Present **
Jasminium Jasminium sp Present **
Nerium Nerium oleander Present **
Catharanthus Catharanthus alba Present **
Hibiscus flower Hibiscus rosa-sinensis Not found
Tree crops
Cocoa trees Theobroma cacao Not found
Mango trees Mangifera indica Present **
Orange trees Citrus sinensis Not found
Pawpaw trees Carica papaya Not found
Weeds
Grass Heliopsis sp Present **
** = More than ten adult thrips collected per leaf/ flower of each plant species
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Table 3:Thrips species identified from associated host plants across some localities in Greater Accra and Eastern Region
S/N Scientific Name Family Subfamily Host Plant
1 Acaciothrips  ebneri, Karny Phlaeothripidae Phlaeothripinae Capsicum annuum
2 Aleurodothrips fasciapennis, Franklin Phlaeothripidae Phlaeothripinae Capsicum annuum
3 Antillothrips sp* Phlaeothripidae Phlaeothripinae S. melongena, Abelmoscus esculentum
4 Chirothrips sp Thripidae Thripinae Vigna unguiculata
5 Dendrothrips sp* Thripidae Dendrothripinae Vigna unguiculata,
6 Dolichothrips sp* Phlaeothripidae Phlaeothripinae Vigna unguiculata
7 Eurhynchothrips sp Phlaeothripidae Phlaeothripinae Brassica oleracea var. capitata
8 Frankliniella shultzei, Trybom Thripidae Thripinae C. annuum, S. lycopersicum, Allium
cepa, C.  annuum var.
9 Haplothrips sp Phlaeothripidae Phlaeothripinae Vigna unguiculata, Rullia blumei, weeds
10 Hercinothrips femoralis, Reuter* Thripidae Panchaetothripinae Capsicum annuum var
11 Karnyothrips sp* Phlaeothripidae Phlaeothripinae Solanum melongena, Brassica oleracea
var. botrytis
* = Thrips species captured by sticky trap on the field
S/N = Number of thrips species identified
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Table 3 cont’d:Thrips species identified and associated host plants.
S/N Scientific Name Family Subfamily Host Plant
12 Megalurothrips sjostedti, Trybom Thripidae Thripinae V. unguiculata,  S. melongena, T. erecta, Verbena
13 Microcephalothrips abdominalis, Crawford* Thripidae Thripinae Brassica oleracea var. botrytis, S.  melongena
14 Panchaetothrips noxius, Priesner Thripidae Panchaetothripinae Apium graveolensvar. dulce, Glycine max
15 Podothrips denticeps, Hood* Phlaeothripidae Phlaeothripinae Solanum melongena
16 Retithrips syriacus, Mayet* Thripidae Panchaetothripinae Apium graveolensvar. dulce
17 Selenothrips rubrocinctus, Giard Thripidae Panchaetothripinae Capsicum annuum
18 Sericothrips adolfifriderici, Karny Thripidae Thripinae Vigna unguiculata
19 Stenchaetothrips melanurus, Bagnall* Thripidae Thripinae Rullia blumei
20 Stictothrips maculatus, Hood* Phlaeothripidae Phlaeothripinae Capsicum annuum var
21 Taeniothrips xanthocerus, Hood Thripidae Thripinae Lactuca sativa,  Portulaca grandiflora
22 Thrips palmi, Karny Thripidae Thripinae Cucumis sativus, Solanum melongena,  Capsicum
annuum var., Solanum macrocarpon
23 Thrips tabaci, Lindeman Thripidae Thripinae Allium cepa, Cucumis sativus, Citrullus lanatus
* = Thrips species captured by sticky trap on the field. S/N = Number of thrips identified.
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Table 4:Number of thrips species on permanent slide mounts identified from various vegetable crops
Host plant
Solanum melongena 4 1 - - - - - - 4 1 - 1 - - - 1 12
Vigna unguiculata 1 9 - - - - 4 1 2 1 - - 2 - - 20
Solanum macrocarpon 2 4 3 - - 1 - - 3 - - - - - - - 13
Allium cepa 10 - 1 1 - - 1 - - - - - - - - - 13
Solanum lycopersicum 4 3 - - - - - - - - - - - - - - 7
Capsicum annuum 1 2 - - 1 1 1 - 2 2 - - - - 1 - 11
Capsicum annuum var. 5 2 1 - - - - - - - - - - - - - 8
Cucumis sativus 1 1 2 - - - - - 1 - - - - - - - 6
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Frankliniella
schultzei
Megalurothrips
Thrips tabaci
Stenchaetothrips
Selenothrips sp
Eurhynchothrips
Aleurodothrips sp
Sericothrips sp
Thrips palmi
Chirothrips sp
Haplothrips sp
Karnyothrips sp
Taeniothrips sp
Dolichothrips sp
Acaciothrips sp
Podothrips sp
Total Number of
thrips
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Table 4 cont’d:Number of thrips species on permanent slide mounts identified from various vegetable crops
Host plant
Amaranthus sp 2 - - - - - - - 6 - - - - - - - 8
Hibiscus sabdariffa - 4 - - - - - - - - - - - - - - 4
Br. ole va  botrytis - - - - - - 1 - - - - 1 - - - - 2
Citrullus lanatus - - 1 - - - - - - - - - - - - - 1
Allium fistulosum - - - - - - 1 - - 1 - - - - - - 2
Abelmoscus esculentum 1 1 - - - - - - - - - - - - - 2
Lactuca sativa - 1 - - - - - - - - - 1 - - - 2
Brassica oleracea var. 1 1 - - - 1 - - - - - - - - - - 3
capitata
Total number of thrips 32 29 8 1 1 3 4 4 17 6 1 2 1 2 1 1 115
per crop
39
Frankliniella
schultzei
Megalurothrips
Thrips tabaci
Stenchaetothrips
Selenothrips sp
Eurhynchothrips
Aleurodothrips sp
Sericothrips sp
Thrips palmi
Chirothrips sp
Haplothrips sp
Karnyothrips sp
Taeniothrips sp
Dolichothrips sp
Acaciothrips sp
Podothrips sp
Total Number of
thrips
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Table 5: Number of thrips species on permanent slide mounts identified from various ornamental plants
Host plant
Jasminium 3 1 - - - - - - - - - - - - - - 4
Neriumoleander - 2 1 - - - - - - - - - - - - - 3
Catharanthus alba - 1 - - - - - - - - - - - - - - 1
Thurmbergia erecta - 5 - - - - - - - - - - - - - - 5
Rullia blumei - 3 - 1 - - - - - - 1 - - - - - 5
Verbena sp - 3 - - - - - - - - - - - - - - 3
Portulaca grandiflora - - - - - - - - - - - - 2 - - - 2
Solanum torvum - 4 - - - - - - - - - - - - - - 4
Heliopsis sp - - - - - - - - - - 4 - - - - - 4
Total 3 19 1 1 - - - - - - 5 - 2 - - - 31
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Frankliniella
schultzei
Megalurothrips
Thrips tabaci
Stenchaetothrips
Selenothrips sp
Eurhynchothrips
Aleurodothrips sp
Sericothrips sp
Thrips palmi
Chirothrips sp
Haplothrips sp
Karnyothrips sp
Taeniothrips sp
Dolichothrips sp
Acaciothrips sp
Podothrips sp
Total per plant
species
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4.3 Insect identification
The morphological features that helped in the identification of Thrips palmi, Thrips tabaci,
Frankliniella schultzei and Megalurothrips sjostedti are as follows:
4.3.1 Thrips palmi Karny
Adult is yellow in colour (Plate 4a) with dark setae. The antenna is seven segmented, with
antennal segment VII being shorter than segment VI (Plate 4b). Antennal segments VI-VII are
brownish distally. The head bears a pair of ocellar setae arising just outside the ocellar triangle.
The ocelli are red-pigmented (Plate 4c). The forewing is pale in colour. The pronotum of T.
palmi has two pairs of posteroangular setae. The anterior end of metanotum possesses distinct
transverse lines and toward the posterior end are present a pair of campaniform sensilla.
a b c
Plate 4: (a)Adult T. palmi (b) Seven segmented antennae of an adult T. palmi (c) Head of an
adult T. palmi showing red-pigmented ocelli.
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4.3.2 Thrips tabaci Lindeman
The body colour of adult is highly varied, ranging from yellow to brown (Plate 5a) depending on
temperature during development. It bears seven segmented antennae (Plate 5b). Antennal
segments III-IV brown with pale basal halves. Unlike Thrips palmi, its ocellar pigment is usually
grey and never red. Forewing is pale in colour. The head bears ocellar setae whose bases arise
within the ocellar triangle.
a b
Plate 5:(a) Adult Thrips tabaci,(b) Seven segmented antennae of an adult
4.3.3 Frankliniella schultzei Trybom
Both sexes are fully winged. Two forms exist; dark-brown (Plate 6a) and yellow forms. It bears
eight-segmented antennae (Plate 6b). Antennal segments III-IV bear forked sensorium. Antennal
segments III-V appear yellowish at least at bases. Antennal segment VIII is longer than segment
VII (Plate 6b). Ocellar setae present and arise close together between anterior margins of the
hind ocelli. F. schultzei lack the campaniform sensilla on the metanotum.
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a b
Plate 6:(a) Adult F. schultzei(b) Antenna of an adult F. schultzeiwith eight antennal segments
4.3.4 Megalurothrips sjostedti Trybom
s
Adults appear dark to brown (Plate 7a) in body colour. The antennae are eight-segmented with
paler antennal segment III(Plate 7b). Forewings bear a small gap in setae row. Abdominal tergite
VIII possesses a number of microtrichia grouped anterolateral to the spiracles.
a b
Plate 7:(a) Adult M. sjostedti, (b) Head of adult M. sjostedti showing paler antennal segment III
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4.4 Farmers’ knowledge of thrips and insecticide usage pattern
4.4.1 Farmers’ knowledge of thrips
A Questionnaire (Appendix 1) was used to obtain data through interviews. Most (71%) of the
farmers interviewed did not know thrips and only 29% of them knew and had experienced thrips
on their crops. Apart from thrips, farmers also mentioned some insect pests they encounter on
their crops. These insects include; white flies, aphids, Diamond Back Moth (DBM) larvae,
caterpillars and leaf miners; with DBM larvae (27.8%), Aphids (25%) and White flies (22.2%)
being the most mentioned of these pests (Figure 3).
30
25
20
15
10
5
0
White flies Aphids DBM larvae Caterpillars Leaf miners
Insect species
Figure 3:Percentage response on farmers’ knowledge of insects other than thrips on crops
infesting crops assessed using survey questionnaire.
4.4.2 Insect pest control
In all the farms visited, insecticide application was the only insect pest control method practiced.
Farmers used a wide variety of insecticides and other agro-chemical products to combat insect
pests and fungal attacks (Table 6). Attack® 5%WDG, Anty Ataa®and Cydim super®were the
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most commonly used insecticides with Attack® 5%WDG as the highest (33%) insecticide used
by farmers against insect pests (Figure 4). Farmers acquired knowledge on insect pest control
through personal experience in vegetable cultivation, fellow farmers and Agricultural extension
officers.
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30
25
20
15
10
5
0
Insecticide used
Figure 4: Percentage response on insecticides used by farmers against insect pests during survey.
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Farmers (%)
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Table 6: Commonly used pesticides and their active ingredients.
Insecticide/Agro-chemical Active Ingredient
Attack® 5%WDG 5% Emamectin Benzoate
Anty Ataa® 200 g/L Imidacloprid
Cydim Super® 400 g Dimethoate and 36 g Cypermethrin
Golan SP Actemiprid
Agrithane® 800 g/Kg Manco-zeb
Plan D Deltamethrin
Mektin 1.8ECTM Abamectin
Lambda-Cy ECTM 25 g/L Lambda-Cyhalothrin
Conti-zeb Manco-zeb
Dursban ®E 480 g/L Chlopyriphos
Deltamethrin Deltamethrin
Topsin-M Methylthiophanate
Conti-halothrin Cyhalothrin
Cuprofix 30 DISPERSS 30% Manco-zeb and 12% Copper Sulphate
Caldon® Dinoseb
Top Cop® Basic Copper Sulfate
Dimethoate Dimethoate
K-Optimal 35 EC 15 g/L Lambda-Cyhalothrin and 20 g/L
Acetameprid
Pyganic  EC 1.4 Pyrethrum
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4.5 Population trends of thrips
4.5.1 Trap Performance in capturing thrips
A total of 13367 adult thrips were captured by all traps out of which 8206 (61.4%) and 5161
(38.6%) thrips were captured by the Blue and Yellow traps respectively. However, there was no
significant difference (ANOVA: Fpr =0.363, DF = 1, P > 0.05 = α) among trap catches
(Appendix 2).Figure 5 shows mean (± S.E) number of thrips caught by different trap types in
five different fields from September 2014 to March 2015.
14
12
10
8
6
4
2
0
Blue trap Yellow trap
Trap type
Figure 5:Mean (± S.E) number of thrips caught by different trap types in five different fields
from September 2014 to March 2015
The mean trap catches among localities showed a significant difference (Fpr = 0.007, DF = 4, P
< 0.05 = α) (Appendix 3) as well as among sampling months (ANOVA: Fpr = 0.049, DF = 6, P <
0.05 = α)(Appendix 4). More thrips per trap (mean: 14 ± 2.5) were captured at Opebia while
Dzorwulu had the least thrips count per trap per week (Figure 6). There was no significant
difference in mean thrips count per trap among Opebia, University of Ghana farm and Haatso but
47
Mean number of thrips per
trap/week/field
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Opebia and University of Ghana farm recorded significantly higher number of thrips compared
to those from East Legon and Dzorwulu. The mean trap catches for September, October,
November, December and March were not significantly different but significantly different from
those of January and February. A higher mean number of thrips per trap were captured in
October during the study (Figure 7).
20
15
10
5
0
Opebia Haatso Dzorwulu East Legon University of
Locality Ghana Farm
Figure 6: Mean (± S.E) number of thrips per trap captured in different localities September 2014
to March 2015
25
20
15
10
5
0
SEP Oct Nov Dec Jan Feb Mar
Month
Figure 7: Mean (± S.E) number of thrips per trap captured in different months from September
2014 to March 2015
48
Mean  number of thrips per Mean number of thrips
trap per field per trap
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4.5.2 Abundance of adult thrips on Vegetable crops
The mean number of thrips among various vegetable crops surveyed showed significant
differences (Fpr = 0.012, DF = 12, P < 0.05 = α) (Appendix 5). There was no significant
difference in mean thrips count per plant between eggplant and cucumber but both were
significantly different from the rest of the crops surveyed (Table 7).
4.5.3 Abundance of Thrips palmi and associated thrips species on vegetable crops
Survey results for abundance of Thrips palmi on some vegetable crops showed no significant
difference (ANOVA: Fpr = 0.099, DF = 1, P > 0.05 = α) (Appendix 6) in mean number of adults
and larvae of thrips. The mean number of adult T. palmi per plant was not significantly different
among selected host plants (AONVA: Fpr = 0.629, DF = 3, P > 0.05 = α) (Appendix 6).Although
there was no significant difference among host plants, more adult thrips than larvae were
collected from the surveyed plants except for cucumber plants where more (18 ± 6.7) larvae were
captured. Higher (22.5 ± 6.6) number of adult thrips was collected on eggplant (Figure 8). In the
course of sampling the four host plants for T. palmi, other thrips species were identified and the
most abundant species besides T. palmi was Megalurothrips sjostedti followed by Frankliniella
schultzei. Only T. palmi was identified on cucumber plants during this survey (Figure 9).
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Table 7: Mean (± S.E) number of thrips per vegetable crop across various localities surveyed.
Plant species Mean (±S.E) number of thrips
Eggplant a5.5 (6 ± 1.1)
Cucumber a4.8 (5 ± 1.2)
Cauliflower b2.7 (3 ± 0.7)
Gboma b2.7 (3 ± 0.5)
Onion b2.6 (3 ± 0.7)
Cowpea b2.6 (3 ± 0.5)
Pepper b2.5 (3 ± 0.4)
Okra b2.2 (2 ± 0.4)
Amaranthus bc1.6 (2 ± 0.2)
Sweet pepper cd1.2 (1 ± 0.3)
Cabbage cd0.6 (1 ± 0.2)
Lettuce d0.3 (0 ± 0.1)
Tomato d0.3 (0 ± 0.1)
LSD 1.2
Means followed by the same letter are not significantly different at 5% probability level.
30 Adults
25 Larvae
20
15
10
5
0
Gboma Sweet pepper Egg plant Cucumber
Plant species
Figure 8: Mean (± S.E) number of adult and larval thrips per plant collected over six weeks
February to March 2015.
50
Mean  number of thrips per
plant
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7 T. palmi
M. sjostedti
6
F. schultzei
5
4
3
2
1
0
Gboma Sweet pepper Eggplant Cucumber
Plant species
Figure 9: Mean (± S.E) number of adult thrips species per plant collected over six weeks
February to March 2015.
4.5.4 Within plant distribution of Thrips palmi
The mean number of adults on cucumber leaves were not significantly different from mean larval
counts (P = 0.163, P > 0.05 = α, DF = 1) (Appendix 7). There were significant differences in
mean numbers of thrips among young, middle and bottom leaves (ANOVA: (P = 0.004, P <0.05
= α, DF = 2)(Appendix 7). The significant difference was found to occur between the young and
bottom leaves (q(YL, BL) = 5.337 > q-critical = 3.532, α = 0.05) (Appendix 8). Figure 10 shows
interaction between mean number of adult and larvae of T. palmi. It indicates that the number of
thrips decreased from young leaves (mean = 16.2) through middle leaves (mean = 10.1) to the
older bottom leaves (mean = 3.2).
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Mean number of thrips per plant
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25
Adults
22
20 Larvae
16.6
15
10 10.2
5 5
3.6
1.6
0
1 2 3
Leaf stage
Figure 10:Factor Interaction comparison chart of mean number of T. palmi collected at different
levels of cucumber plants (x-axis: 1 = Young Leaf, 2 = Middle Leaf and 3 = Bottom Leaf).
4.6 Relationship between trap catches of thrips and weather factors
In general, there was a negative correlation (P-value = 0.191; α = 0.05) between average weekly
temperature and total weekly trap catches for all study fields (Figure 11). However, individual
fields trap catches for East Legon were positively correlated (P-value = 0.0461; α = 0.05) to
average weekly temperatures (Figure 12). There was a negative correlation (P-value = 0.530; α =
0.05) between total weekly rainfall and total weekly trap catches (Figure 13).
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Group means
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1200 y = -71.262x + 2455.9
R² = 0.0603
1000
800
600
400
200
0
25 26 27 28 29 30 31
Average Weekly Temperature
Figure 11:Average weekly temperature and total weekly trap catches of thrips from vegetable
crops in some parts of Greater Accra (September 2014 to March).
350
300 y = 21.593x - 568.95
R² = 0.1346
250
200
150
100
50
0
25 26 27 28 29 30 31
-50
Average Weekly Temperature
Figure 12:Average weekly temperature and total weekly trap catches of thrips for one vegetable
farm (East Legon) in Greater Accra (September 2014 to March).
53
weekly trap catches of thrips
Average weekly trap catches of
thrips
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1200
y = -2.467x + 475.71
1000 R² = 0.0142
800
600
400
200
0
0 10 20 30 40 50 60
Total weekly rainfall
Figure 13:Total weekly rainfall and total weekly trap catches of thrips from vegetable crops in
some parts of Greater Accra from September 2014 to March.
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Total weekly trap catches of thrips
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CHAPTER FIVE
5.0 DISCUSSION
Over twenty species of thrips species were collected from mostly actively growing plant tissues.
This observation confirmed the report by Bailey (1938) that thrips are found on the most tender,
succulent portions of the host plants; usually in buds, in blossoms, under bracts, in leaf sheaths,
or on bulbs. Among several thrips species identified was the melon thrips, Thrips palmi. The
identification of thrips species in this study agrees with Funderburk et al. (2007) who noted that
thrips have been reported in many African countries including Ghana. Banfor (2009) in his M.
Phil. thesis recorded a number of thrips including Megalurothrips sjostedti and Frankliniella
schultzei among others which were also found in this current study. In addition to the thrips
species reported in above cited reports, T. palmi was found to infest several vegetable crops
during this current study. This result varies from reports by EPPO (2015); CABI (2015) and
FVO (2012), indicating that T. palmi was absent in Ghana.
Thrips species infested more than one host plant, confirming polyphagy in thrips as reported by
Kirk (1997b). The author indicated that the flower thrips reproduce and feed in the flowers of
crops and in the absence of flowers, these insects migrate to nearby crops and wild flowers to
continue their cycle. Thrips were also collected from ornamental plants and tree crops, indicating
that these could serve as alternative hosts to thrips when vegetable crops are out of season.
Farmers could easily identify other insects but only a few could identify thrips. This difficulty in
identifying thrips by farmers could be attributed to the small size of an adult thrips compared to
other insect pests which are relatively larger. Even in farms with high infestation of thrips, the
farm owners did not know what the problem was.
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Farmers relied on chemical insecticides for pest control, with Attack®, Anty Ataa® and Cydim
Super® being widely used. This is confirmed by Odhiambo et al. (2010) who pointed out that in
an attempt to protect vegetable crops from high pressure from insect pests, farmers rely mainly
on indiscriminate and widespread use of synthetic insecticides in vegetable cultivation and this
has led to insecticide resistance development in the insect pests. Unfortunately, these insecticides
were not applied specifically for thrips pests, confirming the lack of knowledge of thrips. This
result is partly in line with the report by Daniela et al. (2008) whose findings indicated that
inappropriate management of pesticides use is a cause for concern.
In most farms visited, more than one crop was grown and this could probably account for spread
of thrips since thrips are polyphagous. Farmers acquired farming and pest control practices from
their several years of experience, fellow farmers as well as from Agricultural extension officers.
This result was in agreement with a report by Adu-Dapaah and Oppong-Konadu (2002) who
found that farmers adhered to good agronomic practices most of which were acquired from
colleagues and/or from several years of experience in tomato growing or from agricultural
extension officers. However, there were variations in the way this knowledge was translated into
actual farm practice since no particular pattern was observed.
The improvised Blue and Yellow sticky traps effectively captured thrips species. Generally, there
was no significant difference (Fpr =0.363, P > 0.05 = α) in mean number of thrips among Blue
and yellow traps, although the blue trap captured more thrips than the yellow trap. This
suggested that the two trap colours used did not have a significant influence over number of
thrips trapped. Natwick et al. (2007) reported that Blue traps consistently captured more adult
Thrips tabaci and Frankliniella occidentalis than Yellow traps in onion and lettuce fields.
However, the work by Natwick et al. (2007) was carried out over a short period of two months.
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The study locality probably had an effect on the general trap performance as there was a
significant difference in mean trap catches among localities (Fpr = 0.007, P < 0.05 = α).
Even though there was an overall negative correlation between temperature and trap catches of
thrips, the correlation was not significant (R2 = 0.0603, P = 0.191 >α = 0.05). This negative
correlation could likely be due to the fact that weather data was not collected directly on the
fields where traps were placed, but from a Meteorological agency at Mempasem. The number of
thrips in sticky traps from one locality (East Legon) was significantly positively correlated (R2 =
0.1346, P = 0.0461, α = 0.05) with average weekly temperature, thus confirming a report by Kirk
(1997) who stated that weather variables such as rainfall and temperature have significant effects
on thrips numbers. Relatively high temperatures and lack of rainfall have been associated with
increase in onion thrips population. Boissot et al. (1998) reported a decrease in density of thrips
before the mean temperature reached its maximum and that higher rainfall and high relative
humidity were responsible for the thrips population decrease.
In the present study, total weekly thrips counts decreased with increase in total weekly rainfall,
suggesting that higher rainfall probably decreased thrips population in sticky traps as reported by
Kirk (1997). Results of this study suggested that all four plant species surveyed for T. palmi were
infested with Thrips palmi. The number of thrips species other than Thrips palmi found on the
crops was relatively small, suggesting an insignificant damage potential by these species. Thrips
palmi was thus the major pest of concern. Garima et al. (2010) also found Thrips palmi alongside
Frankliniella schultzei on cucumber plants. However, Thrips palmi was relatively less abundant
and so cucumber was considered the main host for F. schultzei in the above cited report.
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In this present study, larval counts were slightly higher than adult counts on cucumber for T.
palmi. However, this difference was not significant. Adult counts were higher than larval counts
in other plants, thus, these crops could be considered as less suitable hosts of the pest. This
observed pattern could be attributed to the fact that no thrips were found in flowers of cucumber
during this study in the study site, thus making T. palmi more abundant. Talekar (1991) and
Nakahara (1984) reported a serious infestation of T. palmi detected worldwide on plants from
family Solanaceae (eggplants, pepper, and potato), Cucurbitaceae (cucumber, watermelon,
cantaloupe, and squash), and Leguminosae (kidney bean, snap bean, broad bean, cowpea,
soybean, and white clover).
There was a significant difference among mean thrips counts from young leaves, middle leaves
and bottom leaves of cucumber when within plant distribution of T. palmi was studied on
cucumber plants. Thrips palmi was reported by Kawai (1990) to be well adapted to young tissues
of eggplant and cucumber, which provided high food resources. Capinera (2000) reported that
Thrips palmi has a wide host range and prefers host of family Cucurbitaceae and Solanaceae,
where adults and larvae preferably feed on leaves of host plant. Garima et al. (2010) found
Thrips palmi on leaves of cucumber plants in the course of studying the abundance of F.
schultzei. However, Garima et al. (2010) did not state the preferred plant part infested by the
pest. In this present study, Thrips palmi preferred the young leaves to the older-bottom ones.
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CHAPTER SIX
6.0 CONCLUSION AND RECOMMENDATIONS
6.1 CONCLUSION
The results of this study revealed an extension of the existing list of thrips species recorded in
Ghana. The invasive Thrips palmi was identified for the first time in Ghana on vegetable crops
including eggplants (Solanum melongena), gboma (Solanum macropon), sweet pepper
(Capsicum annuum var.) and cucumber (Cucumis sativus). Thrips palmi like other thrips species
is polyphagous; closely associated with several vegetable crops and is cosmopolitan as the pest
was identified in several localities surveyed during this study. Thrips were present throughout the
dry and rainy seasons, but tended to increase during dry seasons especially in the presence of
host plants.
Thrips palmi prefers and is closely associated to the young, succulent cucumber leaves based on
studies on within plant distribution of the pest on cucumber at Haatso, one of the vegetable
growing areas in Accra metropolis.
Based on the number of thrips captured by sticky traps, both the Blue and Yellow coloured
sticky traps can be used alongside visual inspection of crops for a better thrips pest monitoring
program. The sticky traps could however be more convenient in detecting early and small
populations of thrips in the field to inform quick control measures against negative effects of
population build-up.
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6.2 RECOMENDATIONS
It is imperative for major stakeholders in pest management programmes including; Agricultural
extension workers, Universities as well as the Ministry of Food and Agriculture to intensify the
education of vegetable and fruit crop growers on how to distinguish thrips from other insect pests
to enable them apply specific management strategies, especially now that horticultural sector is
faced with interceptions by the European Union, one of the main market outlets for Ghanaian
horticultural produce.
Similar work should be carried out in other Regions of Ghana to establish the presence or
otherwise of Thrips palmi for the whole country especially in vegetable and fruit crop growing
areas. The improvised sticky traps used in this study are not only effective, but also cheap and
easy to produce by small scale vegetable crop farmers.
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REFERENCES
Adu-Dapaah, H. K. and Oppong-Konadu, E. Y. (2002). Tomato production in four major
tomato-growing districts in Ghana: Farming practices and production constraints.
Ghana Jnl agric. Sci., 35:11-22
Amateur Entomologists’ Society (2015). Thrips (Order: Thysanoptera) accessed
fromwww.amentsoc.org/insects/fact-files/orders/thysanoptera.html, accessed 31
March 2015
Bailey, S. F. (1938). Thrips of economic importance California. Berleley, Calif.: University of
California, College of Agriculture, Agricultural experiment station. Circular 346:73-
77
Banfo, M. (2009). Thrips (Thysanoptera; Thripidae) host preference among horticultural crops
in some parts of Ghana (M.Phil. Thesis), ARPPIS, University of Ghana, Legon
Bethke, J. A, Dreistadt, S. H. and Varela, L. G. (2014). Thrips: IPM for home Garden and
Landscape professionals. Pest Notes publication 7429, University of California
Bielza, P. (2008). Insecticide resistance management strategies against the western flower thrips,
Frankliniella occidentalis. Pest Management Science 64: 1131-1138
Bielza, P. Quinto, V. Contreras, J. Torne, M. Martin, A. and Espinosa, P. J. (2007b).
Resistance to spinosad in the western flower thrips, Frankliniella occidentalis
(Pergande), in greenhouses of south-eastern Spain. Pest Management Science 63:
682-687
61
University of Ghana http://ugspace.ug.edu.gh
Boissot, N. Reynaud, B. and Letourmy, P. (1998). Temporal analysis of western flower thrips
(Thysanoptera : Thripidae) population dynamics on Reunion Island. Environmental
Entomology, 27(6): 1437-1443
CABI, (2015).Invasive Species Compendium: Thrips palmi, accessed from
www.cabi.org/iscdatasheet/53745, on 2 January 2015
Cantisano, A. (1999). Onion thrips cause trouble in many regions. Growing for Market.
December, 8.9
Capinera, J. L. (2000). Melon thrips. Featured Creatures. EDIS. Entomology and Neonatology
Department, IFAS, University of Florida
Capinera, J. L. (2008). Encyclopaedia of Entomology, 2nd Edition, Springer, Dordrecht, the
NetherlandsVols. 1–4: 2335–2337
Childers, C. C. and Anchor, D. S. (1991). Feeding and oviposition injury to flowers and
developing floral buds of 'navel' oranges by Frankliniella bispinosa (Thysanoptera:
Thripidae) in Florida. Ann Entomol Soc Am 84: 272-282
Coviello, R. Chaney, W. E.  and Orloff, S. (1993). Onion and Garlic Pest Management
Guidelines. University of California Statewide IPM Program. Davis, CA. UC ANR
Publication 3453
Daniela, H. Melinda, S. Ramatu, A. José, F. and Samuel, E. T. (2008). Insecticide Use on
Vegetables in Ghana: Would GM Seed Benefit Farmers? IFPRI Discussion Paper
00785, 1-36
62
University of Ghana http://ugspace.ug.edu.gh
Dawn.com (2014). EU warns fruit exporting countries, accessed from
Http://www.freshplaza.com/article/124021/EU-warns-fruit-exporting-countries, on
30th January 2015
EC, Europhyte 2013 Food and Veterinary Office Annual Report (2014). EU annual report
on plant health interception from third-country suppliers, accessed
fromhttp://ec.europa.eu/food/plant/plant_health_biosafety/europhyt/docs/annu, on 08
June 2015
Ellington, C. P. (1980). Wing mechanics and take-off preparation of thrips (Thysanoptera). J
Exp Biol 85: 129-136
EPPO (2015). Global Database:Thrips palmi (THRIPL) accessed from
https://gd.eppo.int/taxon/THRIPL/distribution/GH on 8th June 2015
EPPO/CABI (1996a). Frankliniella occidentalis. In: Quarantine pests for Europe. 2nd edition
(Ed. by Smith, I. M, McNamara D. G, Scott P. R, Holderness M). CAB
INTERNATIONAL, Wallingford, UK
EPPO/CABI (1996b). Tomato spotted wilt tospovirus. In: Quarantine pests for Europe 2nd
edition (Ed. by Smith I. M, McNamara D. G, Scott P. R. and Holderness M). CAB
INTERNATIONAL, Wallingford, UK
Final report of an audit carried out in Ghana from 24 April to 03 May 2012. Part of Food
and Veterinary Office’s (FVO) planned audit programme. Ref. Ares (2012) 860901 -
13/07/2012
63
University of Ghana http://ugspace.ug.edu.gh
Fournier, F. Guy, B. and Robin, S. (1995). Effect of Thrips tabaci (Thysanoptera: Thripidae)
on  yellow onion yields and economic thresholds for its management. Entomological
Society of America. 88(5) 1401-1407
Freshfruitplaza.com (2014). EU closes door on Ghanaian vegetable imports, accessed
fromHttp://www.freshfruitportal.com/2014/07/31/eu-closes-door-on-ghanaian-
vegetables-imports, on 31st March 2015
Funderburk, J. Diffie, S. Sharma, J. Hodges, A. and Osborne, L. (2007). Thrips of
Ornamentals in the South eastern US, Entomology and Nematology Department,
Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences,
University of Florida
Garima, K. Dakshina, R. S. and Vivek, K. (2010).Frankliniella schultzei Trybom (Insecta:
Thysanoptera: Thripidae). Entomology and Nematology Department, University of
Florida
Hamdy, M. K. and Salem, M. (1994). The effect of plantation dates of onion, temperature and
relative humidity on the population density of the onion thrips, Thrips tabaci Lind in
Egypt. Ann. Agric. Sci. Univ. Ain. Shams (Egypt).39(1):417-424
Hector, A. A. (2006). A Study of the behavior, ecology, and control of flower thrips in
blueberries towards the development of an integrated pest management (IPM)
program in Florida and Southern Georgia. PhD Thesis, University of Florida: 167p
Hoffmann, M. P. Curtis, H. P. and Anne, C. F. (1996). Integrated Pest Management for
Onions. Cornell University. Cornell, NY. 78p
64
University of Ghana http://ugspace.ug.edu.gh
Infonet-biovision, (2014). Thrips, accessedfromhttp://www.infonet-biovision.org/thrips, on 29th
September 2014
Kambiz, M.  (2014). A new species of Eremiothrips from Iran (Thysanoptera: Thripidae). ACTA
Entomologica Musei Nationalis Pragae, 54(1): 29–34
Karny, H. H. (1925). Die an Tabak auf Java und Sumatra angetroffenen Blasenfusser
(Thysanoptera). Bull. Deli Proefstation. 23: 3–55
Kawai, A. 1990. Life cycle and population dynamics of Thrips palmi Karny. JARQ, 23 (4): 282–
288.
Kay, I. R. and Herron, G. A. (2010). Evaluation of existing and new insecticides including
spirotetramat and pyridalyl to control Frankliniella occidentalis (Pergande)
(Thysanoptera: Thripidae) on peppers in Queensland. Australian Journal
ofEntomology 49: 175-181
Kirk, W. D. J. and Hamilton, J. G. C. (2004). Evidence for a male-produced sex pheromone in
the western flower thrips Frankliniella occidentalis. J Chem Ecol.
Kirk, W. D. J. (1987). How much pollen can thrips destroy? Ecol Entomol 12: 31-40
Kirk, W. D. J. (1997a). Feeding. In T. Lewis [ed.], Thrips as crop pests. CAB International,
Wallingford, UK, 119-174
Kirk, W. D. J. (1997b). Distribution, abundance and population dynamics. In T. Lewis [ed.],
Thrips as Crop Pests. CAB International, Wallingford, UK, 217-258
Kirk, W. D. J. (1997). Feeding, In T. Lewis [ed.], Thrips as Crop Pests. CAB
International,Wallingford, 119-174
65
University of Ghana http://ugspace.ug.edu.gh
Kuepper, G. (2004). Thrips Management Alternatives in the Field. NCAT Agriculture Specialist.
ATTRA publication #IP132
Lathman, L. J. and Jones, R. A. C. (1997). Ocurrence of tomato spotted wilt tospovirus in
native flora, weeds, and horticultural crops. Aust J Agric Res 48: 359-369
Lewis, T. (1997). Thrips as crop pests. CAB Oxon UK. 740pp
Lewis, T. 1973. Thrips. Their biology, ecology, and economic importance. Academic Press,
London and New York
Lewis, T. 1997. Thrips as Crop Pests. CAB International Oxon, New York
Liburd, O. E. Arévalo, H. A. McAuslane,.H. J and Krewer, G. (2006).Thrips and gall midge
control: InG. Krewer and J. Martin [eds.], Proceedings for the Georgia Blueberry
Conference, Georgia- South Carolina Muscadine Conference, North American
Bramble Growers Association Conference Savannah, GA, 135-138
McCulloch, N. and M. Ota. (2002). Export horticulture and poverty in Kenya. Institute of
Development Studies, Brighton, Sussex BN1 9RE, England.IDS Working Paper 174
Mirab-balou, M. and Xue-xin, C. (2011).The Megalurothrips Genus-Group in Iran
(Thysanoptera: Thripidae). Mun. Ent. Zool, 6(2): 944-952
MoFA (2013). Accra Metropolitan, accessed fromhttp://mofa.gov.gh/site/?page_id=1561, on 15
February 2015
Moritz, G. Kumm, S. and Mound, L. (2004a).Tospovirus transmission depends on thrips
ontogeny. Virus Research 100: 143-149
66
University of Ghana http://ugspace.ug.edu.gh
Moritz, G. Mound, L. A. Morris, D. C. and Goldarazena, A. (2004). Pest thrips of the world:
an identification and information system using molecular and microscopical methods.
Central Biological Information Technology, Brisbane. CD-ROM
Moritz, G. Mound, L. A.  Morris, D. C. and Goldarazena, A. (2004b). Pest thrips of the
world. Visual and Molecular identification of pests thrips. An identification and
information system using molecular and microscopical methods. Lucid- CSIRO
publishing, Collingwood, Victoria, Australia
Moritz, G. O’Donnell, C. and Parrella, M. (2009). Pest Thrips of North America Associated
with Domestic and Imported Crops. QAAFI Biological Information Technology
(QBIT), the University of Queensland, CD-ROM
Mound, L. A. (1996). The thysanoptera vector species of tospoviruses. Acta Horticulturae 431:
298-309
Mound, L. A. (1997). Biological diversity: InT. Lewis [ed.], Thrips as crop pests. CAB
Internationa, Wallingford, UK, 197-216
Mound, L. A. (2013). Homologies and host-plant specificity: recurrent problems in the study of
thrips. Florida Entomologist 96(2): 318-322
Mound, L. A. and Masumoto, M. (2009). Australian Thripinae of the Anaphothrips genus-
group (Thysanoptera), with three new genera and thirty-three new species. Zootaxa,
2042: 1-76
67
University of Ghana http://ugspace.ug.edu.gh
Mound, L. A. and Morris, D. (2007). The insect order Thysanoptera: classification versus
systematics. Zootaxa, 1668: 395–411
Mound, L. A. and Palmer, J. M. (1981). Phylogenetic relationships between some genera of
Thripidae (Thysanoptera). Entomologica Scandinavica, 15: 153-17
Murai, T. (2000). Effect of temperature on development and reproduction of the onion thrips,
Thrips tabaci Lindeman (Thysanoptera: Thripidae), on pollen and honey solution.
Applied Entomol. Zool. 35(4): 499-504
Nagata, T. Almeida, A. C. L. Resende, R. De O. and Avila, A. C. De. (2002). The
transmission specificity and efficiency of tospoviruses, In R. Marullo and L. Mound
[eds.], Thrips and Tospoviruses: Proc. 7th Intl. Symp. Thysanoptera. Australian Nat.
Insect Collection, Canberra, Australia, 45-52
Nakahara, L. M. (1984). New State record: Thrips palmi Karny. Hawaii pest report. Hawaii
Dept. Agric. 4(1):15 p
Natwick, E. T.  Byers J. A.  Chu, C. C. Lopez, M. and Hennberry, T. J. (2007).Early
detection and mass trapping of Frankliniella occidentalis and Thrips tabaci in
vegetable crops. Southwest Entomol. 32: 229-238.
Obeng-Ofori, D. and Ankra, D. A. (2002). Effectiveness of Aqueous neem extracts for the
control of insect pests of cabbage, Brassica oleracea var capitata L, in the Accra
plains of Ghana. Agricultural and Food Science Journal of Ghana 1 (1):83–93
68
University of Ghana http://ugspace.ug.edu.gh
Obuobie, E. Keraita, B. Danso, G. Amoah, P. Cofie, O. O. Raschid-Sally, L. and Drechsel,
P. (2006). Irrigated Urban Vegetable Production in Ghana: Characteristics,Benefits
and Risks. IWMI-RUAF-IDRCCPWF, Accra.
Odhiambo, J. A. O. Gbewonyo, W. S. K. Obeng-Ofori, D. Wilson, M. D. Boakye, D. A. and
Brown, C. (2010). Resistance of diamondback moth to insecticides in selected
cabbage farms in southern Ghana. International Journal of Biological and Chemistry
Science 4(5): 1397-1409
OEPP/EPPO (1989). Data sheets on quarantine organisms No. 175, Thrips palmi. Bulletin
OEPP/EPPO Bulletin 19, 717-720
Owusu, E. O. (1997). Preliminary Biochemical evidence of insecticide resistance development
in Ghanaian populations of cotton aphid, Aphis gossypii Glover (Homoptera:
Aphididae)
Palmer, J. M. (1990). Identification of common thrips of Tropical Africa (Thysanoptera:
Insecta). The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
Tropical Pest Management, 36(1) 27-49
Putnam, W. L. (1942). Notes on the predaceous thrips Haplothrips subtilissimus Hal. and
Aeolothrips meleleucus Hal. Can Entomol 74: 37-43
Rateaver, B. and Gylver, R. (1993). Organic Method Primer Update. The Rateavers, San
Diego, CA. 596 p
Sakimura, K. Nakahara, L. M.and Denmark, H. A. (1986). A thrips, Thrips palmi Karny
(Thysanoptera: Thripidae). Entomology Circular, Division of Plant Industry, Florida
Department of Agriculture and Consumer Services, 280:4p
69
University of Ghana http://ugspace.ug.edu.gh
Samler, J. A. (2012). Abundance and Species Diversity of Thrips (Thysanoptera: Thripidae) in
Cotton, Soybean, and Peanut in Southeast Virginia, and Evaluation of
Cyantraniliprole for Thrips Management. MSc. Thesis Faculty of the Virginia
Polytechnic Institute and State University, U.S.A.
Singh, B. P. (2002). Non-traditional crop production in Africa for export. In: J. Janick and A.
Whipkey (eds.), Trends in new crops and new uses. ASHS Press, Alex., VA, 86–92
Sonya, B. Roger, J. and Coutts, B. (2004).Management of thrips and tomato spotted wilt virus.
Farmnote: Department of Agriculture, State of Western Australia, No. 69
Sparks, A. N. Jr. and Liu, T. X. (2001). Thrips on Onions: Identification and
Management.Extension Entomologist and Research Entomologist. The Texas A and
M University System, L-5397
Talekar, N. S. (1991). Thrips in Southeast Asia: Proc. Regional Consultation Workshop,
Bangkok, Thailand, 13 March 1991. Tainan, Taiwan; Asia Vegetable Res. Dev.
Center.74 p
Terry, L. I. (1997).Host selection, communication and reproductive behavior, InT. Lewis [ed.],
Thrips as crop pests. CAB International Wallingford, UK, 65-118
Thalavaisundaram, S. Grant, A. H. Alan, D. C. and Harley, R. (2008).Pyrethroid resistance
in Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) and implications
for its management in Australia. Australian Journal of Entomology47, 64–69
ThripsWiki (2013). Thrips and Pollination, accessed from http://thrips.info/wiki/Thrips-and-
pollination, on 30/09/2014
70
University of Ghana http://ugspace.ug.edu.gh
Trichilo, P. and Leigh, T. F. (1986). Predation on spider mite eggs by the western flower thrips,
Frankliniella occidentalis, (Thysanoptera: Thripidae), an opportunist in a cotton
agroecosystem. Environ Entomol 15: 821-825
Ullman, D. E. (2005). Thrips vectors & tospoviruses: On the edge of adaptation,
VIIIInternational symposium on Thysanoptera and tospoviruses Pacific grove, CA
Waiganjo, M. M. Gitonga, L. M. and Mueke, J. M. (2008). Effects of weather on thrips
population dynamics and its implications on the thrips pest management. Afr. J. Hort.
Sci. 1:82-90
Wang, C. L. and Chu, Y. I. (1986). Rearing method of southern yellow thrips, Thrips palmi
Karny, in the laboratory. Plant Prot. Bull. (Taiwan, R.O.C), 28:411
Weiss, A. Dripps, J. E. and Funderburk, J. (2009). Assessment of implementation and
sustainability of integrated pest management programs. Florida Entomologist 92:
24-28
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APPENDICES
Appendix 1: Sample Questionnaire
Survey studies on Farmers’ knowledge of Thrips and Insecticide usage pattern
Instructions: Fill in the blank spaces and place a tick where appropriate.
1. Name of survey agent…………………………………………………………………………..
2. Date……………………………………………………………………………………………..
3. Farmers’ name………………………………………………………………………………….
4. Survey site…………………………………………………........................................................
5. Crops cultivated?
..……………………………………………………………………………………………
6. Do you know thrips? Yes, No
7. Which crops do they attack?
.........................../.........................../............................/................................/......................../
............................./.........................../............................../............................/.........................
8. What are some other insects you find on your crops? ....................../ ……………../
…………/ ………………/ ……………………/   ……………./ ………………./ etc……
9. How do you differentiate thrips from other insects on your crops?
......................................................................................................................................................
............................................................................................................................................
10. Where do you find thrips on crops?
a.) Flowers
b.) Leaves
c.) Stems
d.) Others (specify)
11. Thrips pest management practices
Which method do you use in controlling thrips?
a. Chemical control
b. Others (specify)……………………………………………………………………………
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12. If you use chemicals, list the different insecticides you use(d):
…………………………………………………………………………………………………..
………………………………………………………………………………………………….
13. Pattern of use of insecticides
a. Threshold of insects:
Are the insecticides effective? Yes or No
b. How often do you apply insecticides to your crops? ...........................................................
c. How do you use various insecticides?
i) As a mixture
ii) Alternatively (one after the other)
d. Which indicator do you use as a guide to spray?
i) Calendar basis
ii) Presence of thrips
iii) Presence of damage
e. What insecticide dosage do you use on your farm?
i) Below recommended
ii) Recommended
iii) Above recommended
f. What equipment do you use in spraying?
i) Knapsack sprayer (hand operated)
ii) Others
(specify)………………………………………………………………………….
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14. Precaution during insecticide application
a. Do you wear protective clothing during insecticide application?
i) Yes, always
ii) Yes, sometimes
iii) No
b. Insecticide storage
How or where do you store your insecticides?
In rooms/Barns/Tree tops/Boxes in farms/Burry in soil/Keep in hidden bushes
15. Disposal of empty insecticide containers
a. How do you handle empty insecticide containers?
i) Throw them away
ii) Use as water containers
iii) Use in storing seeds
iv) Burry them in the soil
v) Sell them out to other people
16. Source of farmers’ knowledge on pest thrips control
a. Where do you get professional advice on proper use and handling of insecticides?
i) Fellow farmers
ii) Customers
iii) Experience
iv) Mass media
v) Agricultural extension officers
vi) Others (specify)…………………………………………………………………………
b. If by extension officer, how often do you receive such advice?
………………………………………………………………………………………………
17. Where do you buy insecticides? ...............................................................................................
18. What is the interval between insecticide application and subsequent watering?
………………………………………………………………………………………………
19. Do you keep farm records on your insecticide usage patterns? Yes    No.
‘Thanks for your cooperation’
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Appendix 2: Analysis of Variance for trap performance in catching thrips
Source of Variation DF SS MS VR F pr.
Block stratum 4 540.82 135.21 1.43
Treatment (Trap type) 1 99.41 99.41 1.05 0.363
Total 9 1018.32
Appendix 3: Analysis of Variance for effect of study locality on mean trap catches
Source of Variation DF SS MS VR F pr
Locality 4 853.26 213.31 4.34 0.007
Residual 30 1476.01 49.20
Total 34 2329.27
Appendix 4: Analysis of Variance for effect of sampling month on mean trap catches
Source of Variation DF SS MS VR F pr
Month 6 804.46 134.08 2.46 0.049
Residual 28 1524.82 54.46
Total 34 2329.27
Appendix 5: Analysis of Variance for number of thrips and associated plant species
Source of Variation DF SS MS VR F pr
Plant species 12 32.879 2.740 2.36 0.012
Residual 78 90.516 1.160
Total 90 123.395
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Appendix 6:Analysis of Variance for abundance of Thrips palmi on host plants
Source Of Variation SS DF MS F P-value F-crit
Sample
(Adults & larvae) 0.4340 1 0.4340 2.8373 0.0999 4.0848
Columns
(Host plants) 0.2679 3 0.0893 0.5837 0.6292 2.8387
Total 6.8796 47
Appendix 7:Analysis of Variancetable for within plant distribution of Thrips palmi on cucumber
plants (two-factor with replication)
Source Of Variation SS DF MS F P-value F crit
Sample
(YL, ML & BL) 2.5196 2 1.2598 7.1777 0.0036 3.4028
Columns
(Adults & Larvae) 0.3637 1 0.3637 2.0721 0.1629 4.2597
Total 7.3430 29
Appendix 8: Tukey’s Honestly Significant Difference for within plant distribution of Thrips
palmi on cucumber plants
Group Mean Order q-critical
parings differences of pairs q-value (α = 0.05)
(YL, ML) 1.089-0.782 = 0.307 3rd (Smallest) 2.314 3.532
(YL, BL) 1.089-0.381 = 0.708 1st (Largest) 5.337 3.532
(ML, BL) 0.782-0.381 = 0.401 2nd (largest) 3.023 3.532
*YL = Young Leaf, ML = Middle Leaf and BL = Bottom Leaf
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