Botanical Insecticides from Readily Available Ghanaian Plants: a Novel Approach for Sustainable Management of Cabbage Pests

Botanical insecticides from readily available Ghanaian plants: A novel approach for sustainable management of cabbage pests

Blankson Wadie Amoabeng B Sc. (Hons) Agric

A thesis submitted for the fulfillment of the requirements for the degree of

Master of Philosophy

Faculty of Science

School of Agricultural and Wine Sciences

August 2013

Table of contents Page

Table of contents ii

List of tables v

List of figures vi

Abbreviations used in this thesis viii

Publications produced from this thesis ix

Certificate of Authorship x

Acknowledgements xi

Dedication xiii

Abstract xiv

Chapter One 1

1.1 General introduction 1

1.2 General overview of pest management in Ghana 8

1.3 The status of the use of botanical insecticides in Ghana 10

1.4 Prospect for wider use of botanical insecticides in Ghana 12

1.5 General overview of cabbage production in Ghana 14

1.6 Conclusion 18

1.7 Thesis aim and objectives 19

Chapter two 21

2.1 Literature review 21

2.2 The need for safer pest management options 21

2.3 Botanical insecticides 22

2.4 A brief history about botanical insecticides 22

2.5 Active compounds in botanical insecticides 23

2.6 Modes of action of botanical insecticides 24

2.7 Advantages and disadvantages of botanical insecticides 27

2.8 Extraction and purification of plants’ secondary metabolites 31

2.9 Parts of plants used as botanical insecticides 33

2.10 Management of cabbage pest with botanicals 34

2.11 Insecticidal plants used in this study 34

2.11.1 Ageratum conyzoides (Asterales: Asteraceae) goat weed 34

2.11.2 Chromolaena odorata (Asterales: Asteraceae) Siam weed 37

2.11.3 Synedrella nodiflora (Asterales: Asteraceae) Cinderella weed 40

2.11.4 Ocimum gratissimum (Lamiales: Lamiaceae) basils 42

2.11.5 Nicotiana tabacum (Solanales: Solanaceae) tobacco 44

2.11.6 Cassia sophera (Fabales: Fabaceae) sophera senna 47

2.11.7 Ricinus communis (Malpighiales: Euphorbiaceae) castor oil plant 47

2.11.8 Jatropha curcas (Malpighiales: Euphorbiaceae) physic nut 49

2.12 Conclusion 57

Chapter three 60

Tri-trophic insecticidal effects of African plants against cabbage

pests 60

3.1 Introduction 60

3.2 Materials and methods 63

3.2.1 Study site 63 3.2.2 Experimental design and treatment preparation 64 3.2.3 Field cage experiments 64 3.2.4 Data collection 68 3.2.5 Open field experiments 68 3.2.6 Data collection 69 3.2.7 Statistical analysis 70 3.3 Results 71 3.3.1 First trophic level: plant yield and damage 71 3.3.2 Second trophic level: herbivore dynamics 73

3.3.3 Third trophic level: natural enemy dynamics 75

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3.4 Discussion 76 Chapter four 93 Cost: benefit analysis of botanical insecticide use in cabbage: implications for smallholder farmers in developing countries 93

4.1 Introduction 93 4.2 Materials and methods 97 4.2.1 Costs 98

4.2.2 Economic analysis 99

4.3 Results 100

4.3.1 Yield and income 103

4.3.2 Cost: benefit 104

4.4 Discussion 105

4.4.1 Labour cost 105

4.4.2 Cost: benefit ratio 106

4.5 Conclusion 109

Chapter five 111

General discussion and conclusion 111 5.1 Introduction 111 5.2 Field cage t bioassays on P. xylostella and B. brassicae 113

5.3 Effects of the botanicals against cabbage pests in the field 115

5.4 Effects of the botanicals on natural enemies 118

5.5 Effects of botanicals on cabbage yield and quality 119

5.6 Economic implications of botanical insecticides for the smallholding farmer 119

5.7 Recommendations for future research 121

5.8 Conclusions 122

References 125

List of tables Table 1.1 Summary of major insect pests of cabbage in Ghana 16 Table 2.1 Some available insecticidal plants in Ghana 52

Table 3.1 Effect of plant extracts and synthetic insecticides on mean (±SE) yield and heads with borer holes per plot in field experiments during the major rainy season, 2012 at Kumasi, Ghana. 82 Table 3.2 Effect of plant extracts and synthetic insecticides on mean (±SE) percentage reduction of Plutella xylostella numbers and Brevicoryne brassicae infestation score in field cage experiments at Kumasi, Ghana. 83 Table 3.3 Effect of plant extracts and synthetic insecticides on mean (±SE) yield and heads with borer holes per plot in field experiments during the minor rainy season, 2012 at Kumasi, Ghana 84

Table 4.1 Cost and benefit analysis of managing pest of cabbage with botanical insecticides and synthetic insecticide (Attack®) on one hectare farm during the major rainy season of 2012 in Kumasi, Ghana. 101 Table 4.2 Cost and benefit analysis of managing pest of cabbage with botanical insecticides and synthetic insecticide (Attack®) on one hectare farm during the minor rainy season of 2012 in Kumasi, Ghana. 102

List of figures

Figure 3.1 Cages for rearing of Plutella xylostella and Brevicoryne brassicae in cages to obtain cohorts for cage experiment. 66

Figure 3.2 Nursery of cabbage seedling in inset-proof netting for experiments 67

Figure 3.3 Cage experiments set up 67 Figure 3.4 Treatment applications through a side zipper in cage Experiments 68

Figure 3.5 Section of the major rainy season field experiments showing 2m wide alley on the left 70

Figure 3.6 Cabbage heads from plots sprayed with an extract of Ageratum conyzoides 72

Figure 3.7 Cabbage heads from plots sprayed with Attack® 73

Figure 3.8 Cabbage plant from control (sprayed with tap water) plots showing severe Plutella xylostella damage in minor rainy season field experiment. 75

Figure 3.9 Effects of plant extracts and synthetic insecticide on mean (±SE) P. xylostella count in a field experiments during the major rainy season, 2012 at Kumasi, Ghana. 85

Figure 3.10 Effects of plant extracts and synthetic insecticide on mean (±SE) score of B. brassicae score in a field experiments during the minor rainy season, 2012 at Kumasi, Ghana. 86

Figure 3.11 Effects of plant extracts and synthetic insecticide on mean (±SE) B. brassicae score in a field experiments during the major rainy season, 2012 at Kumasi, Ghana 87

Figure 3.12 Effects of plant extracts and synthetic insecticide on mean (±SE) score of B. brassicae score in a field experiments during the minor rainy season, 2012 at Kumasi, Ghana. 88

Figure 3.13 Effects of plant extracts and synthetic insecticide on mean (±SE) count of Coccinellidae in a field experiments during the major rainy season, 2012 at Kumasi, Ghana. 89

Figure 3.14 Effects of plant extracts and synthetic insecticide on mean (±SE) weekly count of Coccinellidae in a field experiments during the minor rainy season, 2012 at Kumasi, Ghana 90

Figure 3.15 Effects of plant extracts and synthetic insecticide on mean (±SE) Syrphidae count in a field experiments during the major rainy season, 2012 at Kumasi, Ghana. 91

Figure 3.16 Effects of plant extracts and synthetic insecticide on mean (±SE) Syrphidae count in a field experiments during the minor rainy season, 2012 at Kumasi, Ghana. 92

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Abbreviations used in this thesis BC Before Christ Bt Bacillus thuringiensis CRI Crops Research Institute

CSIR Council for Scientific and Industrial Research

DBM Diamondback moth DDT Dichlorodiphenyltrichloroethane EC Emulsifiable concentrate EPA Environmental Protection Agency FAO Food and Agriculture Organisation FFS Farmer Field School GLM Generalized linear module IPM Integrated pest management KJ Kilo Joule L Litre LC Lethal concentration

L D Lethal dose

MAE Microwave-assisted extraction MoFA Ministry of Food and Agriculture MRL Maximum residue limit NPAS Northern Presbyterian Agricultural Services SAS Statistical Analysis System

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Publications produced from this thesis

Chapter three and four of this thesis are based on papers prepared for refereed journals. The majority of work in these papers is my own work with authors included for their contribution is experimental design, data analysis and manuscripts preparation. In this thesis, minor changes have been made to the referencing style, table and figure numbers, addition of photos and some text to maintain consistency in format and style throughout the thesis.

Chapter three

Amoabeng BW, Gurr GM, Gitau CW, Nicol HI, Munyakazi L, &

Stevenson PC. (2013) Tri-Trophic Insecticidal Effects of African Plants against Cabbage Pests. PLoS ONE 8(10): e78651.

Chapter four

Amoabeng, B.W., Gurr, G.M., Gitau, C.W. and Stevenson, P.C., (2014).

Cost: benefit analysis of botanical insecticide use in cabbage: Implications for smallholder farmers in developing countries. Crop Protection, 57(0): 71-

76.

Certificate of Authorship

I, Blankson Wadie Amoabeng, hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another or material which to a substantial extent has been accepted for the award of any other degree or diploma at Charles Sturt University or any other educational institution except where due acknowledgement is made in this thesis. Any contribution made to this research by any individual at Charles Sturt University or elsewhere during my candidature is fully acknowledged.

I agree that this thesis be accessible for the purpose of study and research in accordance with the normal conditions established by the Executive

Director, Library Services or nominee, for the care, loan and reproduction of theses.

…………………………. ……………………..

Blankson Wadie Amoabeng Professor Geoff Gurr

(Candidate) (Principal Supervisor)

Acknowledgements

I am very grateful to the Almighty God for His kindness towards me throughout the period of my candidature.

This M. Phil. research was possible with the scholarship provided by the

Australian Government Overseas Aid Programme (AusAID). Council for

Scientific and Industrial Research (CSIR)-Crops Research Institute (CRI)

Ghana, generously offered me full study leave to pursue this training.

School of Agricultural and Wine Sciences, CSU provided funds to cover cost of my field work.

First, I would like to thank my Principal supervisor, Professor Geoff Gurr for his patience, guidance and immeasurable support throughout my study.

You were very accommodative and always welcoming. You have really succeeded in shaping my attitude towards scientific reasoning and writing.

Second, I would like to thank Co-supervisors, Dr Catherine Gitau and

Professor Phil Stevenson for the valuable and timely suggestions you offered throughout my study period. My special appreciation goes to Annie

Johnson (CSU) for her support throughout my study period. You conscientiously read through this thesis and offered very useful suggestions.

Third, I would like to thank Dr M. Owusu-Akyaw, Dr M. B. Mochiah, Dr

Haruna Braimah (CSIR, CRI) and Dr Ken Okwae Fening (University of

Ghana) for the advice and suggestions they offered throughout my study period. You assisted me in every way possible to make this thesis see light.

I would like to express my appreciation to Mr. Anthony Gyimah, Augustine

Agyekum Darkwa, Douglas Antwi, George Kontor Jnr, Ebenezer Adamti,

Gilbert Osei, Johnson Yeboah and the entire staff of the Entomology and

Biocontrol sections, CRI for the assistance you offered during my field work in Ghana. I would like to thank Henry Oti Boateng and Dorcas Amoah for their involvement in all the field activities.

Fourth, my sincere thanks go to the late Professor Louis Munyakazi and Mr.

Kwesi Poku Asare of the department of Mathematics and Statistics, Kumasi

Polytechnic, Ghana, for their immeasurable assistance in the statistical analysis of this thesis. Helen Nicol, CSU also deserves thanks for her assistance in validation and interpretation of some statistical results.

Finally, I would like to thank my family for their support, prayers and encouragement throughout my study period. My special appreciation goes to my wonderful wife, Dorcas Nyarkoa Amoah (Dorcas Wadie Amoabeng) for all the sacrifices you made and the difficulties you endured whilst I was away. You carried and delivered our first child whilst I was away. May God crown all your efforts with joy.

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Dedication

This thesis is dedicated to two important personalities. First, to the blessed memory of my late father, Mr. James Fordjour Wadie who sacrificed everything he had to educate his children. Second, to our first child

Kwabena Amoabeng Wadie, who was born whilst I was away studying in

Australia.

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Abstract

Botanical insecticides are increasingly attracting research attention as they offer novel modes of action that may provide effective management of pests that have already developed resistance to conventional insecticides. They potentially offer cost-effective pest control option to smallholding farmers in developing countries if highly active extracts can be prepared simply from readily available plants. This thesis investigated the potential of using nine readily available Ghanaian plant species: goat weed, Ageratum conyzoides, Siam weed, Chromolaena odorata, Cinderella weed, Synedrella nodiflora (Asteraceae), chilli pepper, Capsicum frutescens, tobacco,

Nicotiana tabacum (Solanaceae), cassia, Cassia sophera (Fabaceae), physic nut, Jatropha curcas, castor oil plant, Ricinus communis (Euphorbiaceae) and basil, Ocimum gratissimum (Lamiaceae) in managing pest of cabbage.

In field cage experiments, the botanicals were tested against cabbage aphid,

Brevicoryne brassicae and diamondback moth, Plutella xylostella. Simple

Sunlight® liquid soap and water extracts of all botanical treatments gave control of cabbage aphid, and diamondback moth comparable to the synthetic insecticide Attack® (emamectin benzoate) and superior to Lambda

Super® (lambda-cyhalothrin), water or Sunlight® liquid soap controls.

Infield experiments in the major and minor rainy seasons using a sub-set of plant extracts (A. conyzoides, C. odorata, N. tabacum, R. communis and S. nodiflora), all controlled B. brassicae and P. xylostella more effectively than water control and comparably with Attack®. The botanicals showed effectiveness against other minor pests such as Hellula undalis, Bemisia tabaci and Pieris rapae though were not included in the statistical analysis of this thesis due to their smaller numbers. Botanical and water treatments

xiv were more benign to predators than was Attack®. Effects cascaded to the yield with all botanical treatments giving cabbage yield per unit area, and most giving head weights, comparable to Attack®. The cost of each treatment including material and labour in the field experiments as well as the revenue derived from both the marketable (undamaged) and damaged yield of cabbage was calculated. The cost: benefit ratios of sprayed treatments were derived by comparing the cost of each plant protection regime against the additional market value of the treatment yield above that obtained in an unsprayed control treatment. With the exception of plots sprayed with an extract of N. tabacum, the cost of plant protection using

Attack® was higher than any of the botanicals in both seasons. In the major rainy season, the highest cost: benefit ratio of 1: 29 was observed for plots sprayed with an extract of C. odorata and was followed closely by N. tabacum treatment with 1: 25 with Attack® recording 1: 18. In the minor season, plots sprayed with Attack® had the highest cost: benefit ratio of 1:

15 and was followed closely by N. tabacum with 1: 14. Botanical insecticides differed markedly in cost: benefit and some were comparable to that from conventional insecticide.

Overall, this thesis showed that simply-prepared extracts from readily- available Ghanaian plants offer cost-effective means of managing pests of cabbage and are safe to beneficial arthropods. These botanicals merit further research as a cheap plant protection strategy for smallholding farmers in

West Africa.

1.1 General introduction Production of crops to cater for the nutritional requirements for the world’s rising human and livestock population is in jeopardy due to the presence of arthropod pests (Oerke & Dehne, 2004). Increasing crop production through enhanced productivity per unit area seems illusive without effective insect pest management. Pest management plays an immeasurable role in protecting crops from pests. Ideally, insecticides should be toxic only to the target pest, biodegradable and non-persistent. However, the desire to quickly and completely eradicate insect pests has led to the use of insecticides that do not meet the above qualities in the current pest management systems in agriculture.

Adoption and implementation of safer pest management options is slow in the developing countries (Kaushik et al., 2009). Food safety issues have attracted global attention due to the direct consequences insecticide- contaminated food have on human health. It is imperative to restore consumer confidence in the safety of food commodities they patronise, especially those that are often eaten raw or partially cooked such as vegetables. This has aroused interest in using benign pest management options such as botanical insecticides.

Besides the production of carbohydrates, proteins and other important nutrients, plants produce an array of compounds called secondary metabolites such as alkaloids, terpenoids, flavonoids and phenols. These compounds are known to have activity against insects and can be used to effectively manage insect pests in a relatively friendly manner (Dubey et al.,

2011). The present study aimed at investigating the insecticidal activity of nine common Ghanaian plants in managing insect pests of cabbage. The approach was to initially review insecticidal plants readily available in

Ghana that might have activity against cabbage pests. A shortlist of nine plants was made from 24 potential insecticidal plants and were tested against the cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae) and the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera:

Plutellidae) in cage plant experiments. Five successful, easy-to-obtain and abundant plant species were selected for field experiments against wider pest range in two seasons (major and minor rainy seasons). For these plant materials to be considered ideal in managing pests, their effect on beneficial insects was considered in the study. Finally, a cost-benefit analysis of using these botanicals in comparison with synthetic insecticide was done to obtain economic justification for their use.

Cabbage, Brassica oleracea var. capitata L. (Cruciferae) is an important temperate vegetable crop but grows well in other climatic regions throughout the world. It is an excellent source of vitamin C and beta- carotene (vitamin A precursor). These anti-oxidants are considered helpful to combat the effects of free radicals in the human body (Timbilla &

Nyarko, 2006). A 100g fresh cabbage contains 103 KJ energy 5.8g carbohydrate, 3.2g sugars, 2.5g dietary fibre, 0.1g fat and many micro nutrients (Asare-Bediako et al., 2010). It is used in several food preparations such as stews, salads, soups, or plain boiled (Asare-Bediako et al., 2010).

Currently, there are no production statistics in Ghana but the crop is widely cultivated and consumed by both urban and rural dwellers, regardless of

2 their economic status in all regions of the country (Timbilla & Nyarko,

2006; Probst et al., 2010; Mochiah et al., 2011).

In Ghana, cabbage is largely produced by market gardeners in the urban and peri-urban centres, nonetheless, some production occurs in other parts of the country (Ntow et al., 2006; Mochiah et al., 2011a). Due to lack of irrigation facilities, cabbage production in the cities is usually concentrated in lowland areas where there is a perennial water supply (Grzywacz et al., 2010;

Mochiah et al., 2011a). Cabbage production is a source of income for families who cultivate the crop all year round. It also provides employment for numerous women who buy at the farm gate and sell directly to the consuming public. Indirectly, the crop provides employment to agro-input dealers, fast-food and restaurant operators. Through export to neighbouring countries, cabbage provides foreign income to the country (Amoah et al.,

2007; Asare-Bediako et al., 2010).

Successful production of cabbage is hampered by abiotic and biotic constraints. As in other parts of the world, diseases and pests pose major biotic constraints to cabbage production in Ghana (Grzywacz et al., 2010;

Waiganjo et al., 2011). Insect pests pose a great challenge to cabbage production. The region has little access to newer and safer insecticides to manage pests (Grzywacz et al., 2010; Waiganjo et al., 2011). Cabbage is usually attacked by caterpillars that cause extensive damage reducing yield and marketability (Zehnder et al., 1997; Sibanda et al., 2000).

The diamondback moth is the most important pest of cabbage in Ghana as in many other countries (Grzywacz et al., 2010). Yield losses from DBM can be high as 100% (Weinberger & Srinivasan, 2009; Waiganjo et al., 2011).

Total cost of management and yield loss associated with DBM globally is estimated between US$4 and 5 billion (Zalucki et al., 2012; Furlong et al.,

2013). Cabbage aphid is important insect pest of cabbage in Ghana and other parts of the world (Mochiah et al., 2011a). Damage caused by aphid through feeding results in poor plant growth and indirect damage can occur from honeydew and mould growth or the transmission of viral plant pathogens (Satar et al., 2005). Cabbage aphid is a vector of 20 plant viruses for a large range of plants (Satar et al., 2005). Other insect species including the cabbage looper, Trichoplusia ni Hübner (Lepidoptera: Noctuidae), cutworms, Agrotis spp. (Lepidoptera: Noctuidae), cabbage web worm,

Hellula undalis Guenée (Lepidoptera: Pyralidae), imported cabbage worm,

Pieris rapae (Lepidoptera: Pieridae), the whitefly, Bemisia tabaci (Genn.)

(Homoptera: Aleyrodidae) and snails (Mollusca) also pose problems to the crop’s success in Ghana.

Application of synthetic insecticides is the main pest management strategy employed by vegetable farmers in Ghana (Gerken et al., 2001; Ntow et al.,

2006; Obopile et al., 2008; Grzywacz et al., 2010). Despite the usefulness of synthetic insecticides in vegetable production, they are expensive and unavailable to the subsistence farmers in remote areas. They are also linked to human and animal health problems and negative environmental impacts

(Upasani et al., 2003; Macharia et al., 2005; Rathi & Gopalakrishnan, 2006;

Devanand & Rani, 2008; Weinberger & Srinivasan, 2009). Over reliance on synthetic insecticides has also resulted in eradication of important natural enemies that could naturally contribute to the management of cabbage pests

(Macharia et al., 2005; Grzywacz et al., 2010). Resistance of the P. xylostella and other insect pests of cabbage to synthetic insecticides is on 4 the rise. Sustainable pest management is a concern of farmers, scientists and other stakeholders in the cabbage production industry (Macharia et al.,

2005; Ntow et al., 2006). For instance, aphid resistance to λ-cyhalothrin

(Bossmate®) resulted in a significant reduction in yield of cabbage compared with plots sprayed with hot pepper and garlic as botanical insecticide (Fening et al, 2011).

Inappropriate handling and use of pesticides continue to pose risk to human health around the globe, especially in the developing world. About 75% of all pesticide poisoning-related deaths occur in developing countries even though they use only 15% of the global pesticide supply (Koul et al., 2004).

Tongue-testing of diluted insecticide to determine its potency is a common practice among some vegetable growers in Ghana (Ntow et al., 2006;

Timbilla & Nyarko, 2006; Williamson et al., 2008) due to their inability to read pesticides labels (Isman, 2008). In the latter part of 2010 in 14 villages in the Upper East region of Ghana, 15 farmers died of suspected pesticide poisoning whilst 46 suffered from pesticides inhalation and 37 were injured from pesticide spillage (NPASP, unpublished report). Reports of pesticide contamination in water, food and human blood and breast milk in areas of intensive vegetable production in Ghana have also emerged (Ntow et al.,

2006; Essumang et al., 2008; Armah, 2011; Bempah et al., 2011).

Integrated pest management (IPM) is the combination of all pest management strategies such as biological, cultural (crop rotation, mixed cropping, intercropping), physical, botanical, chemical in a cost-effective manner with the intention of minimizing the negative environmental impact.

This system recognizes and considers natural enemies as integral component

5 in the crop protection strategy (Koul & Dhaliwal, 2003). Botanical insecticides in an IPM are generally considered safe to natural enemies and the environment and thus, compatible with other pest management tactics.

Certain plants have been observed to prevent insect attack in stored food commodities or field crops. This activity is based on the presence of secondary metabolites such as phenolic compounds, alkaloids, flavonoids and terpenoids. Allelochemicals for instance have been associated with protecting plants against insect herbivory and have long been used for crop protection (Regnault-Roger & Philogène, 2008). Ghana, a tropical country is rich source of diverse flora with various insecticidal properties. Peasant farmers have utilised these insecticidal properties in plants over the years

(Belmain & Stevenson, 2001; Isman, 2008). Pest management with botanicals is considered eco-friendly (Buss & Park-Brown, 2002) low-cost and readily available to local farmers (Belmain & Stevenson, 2001).

Botanical insecticides have been used to manage insect pests in Africa,

Europe, Asia, the USA and the world over (Belmain & Stevenson, 2001;

Bouda et al., 2001; Obeng-Ofori & Ankrah, 2002; Isman, 2006, 2008;

Kianmatee & Ranamukhaarachchi, 2007). Insect pests of crops such as the

DBM and Spodoptera litura (Lepidoptera: Noctuidae) that are known to have developed resistance to several conventional insecticides have been managed successfully with botanicals (Kianmatee & Ranamukhaarachchi,

2007). Botanical insecticides have complex mixtures of active constituents that may together show greater bioactivity than individual component in isolation (Koul, 2004; Rathi & Gopalakrishnan, 2006; Devanand & Rani,

2008). They offer novel modes of action such as oviposition deterrence, repellence, antifeeding activities, and anti-juvenile hormones.

Several secondary metabolites in plant families such as Meliaceae,

Rutaceae, Asteraceae, Piperaceae, Compositae, Lamiaceae, Euphorbiaceae,

Combretaceae and Annonaceae have been identified to possess activity against various pests (Devanand & Rani, 2008). Commercial production of essential oils and plant constituents occurs with some plants such as the

Indian neem tree, Azadirachta indica (A. Juss) (Meliaceae), pyrethrum products (from the flowers of the genus Chrysanthemum), garlic, Allium sativum L. (Asparagales: Amaryllidaceae) and Ryania speciosa

(Malpighiales: Salicaceae). Although some plant-based insecticides have been commercialised, botanical insecticides trail behind chemical insecticides contributing a little over 1% of global insecticide use (Isman,

2000). These commercial products are not available to some farmers due to their isolation and cost of the products. To make botanical insecticides available, easily accessible and attractive to the subsistence farmers, plant materials within their vicinity should be identified and screened for use, enabling farmers to effectively manage pests at the most appropriate times whilst reducing the excessive use of chemical insecticides, and enhancing environmental sustainability and their health and livelihood.

1.2 General overview of pest management in Ghana

Many farmers in Ghana rely on synthetic insecticides to protect their crops in field and in storage (Ntow et al., 2006). According to Gerken et al. (2001) field pesticide use in Ghana by large-scale and small-scale farmers sampled stands at 85 and 74% respectively. The volume of pesticides use has increased tremendously in Ghana. For instance, insecticide imports into

Ghana increased from 907 Mt in 2001 to over 5,078 Mt in 2009 with peaks in 2006 and 2007 of 6921 and 9979 Mt respectively (Avicor et al., 2011).

Unfortunately, majority of the farmers are classified as resource-limited and therefore cannot afford safer synthetic insecticides and thus, rely on highly toxic, persistent and sometimes products that are banned from use (Obeng-

Ofori & Ankrah, 2002).

Pesticides in Ghana are classified by the Environmental Protection Agency

(EPA) of Ghana into four groups; (1) general use, (2) restricted use, (3) suspended pesticide and (4) banned pesticide (Gerken et al., 2001). By 2005 about 25 pesticides, including DDT, Aldrin, and Parathion are known to have been banned in Ghana (Edmund, 2005). This usually is due to persistence in the environment and high toxicity to living organisms. A recent report by the Northern Presbyterian Agricultural Services and

Partners (NPASP, unpublished) shows that some of the banned pesticides including aldrin, dieldrin, endosulfan, lindane, DDT, methylbromide and carbofuran are still on the market and are being used by farmers.

Ghana’s official language is English though, it is not uncommon to find pesticides on the market that are labeled in French or Chinese (Gerken et al.,

2001; Asante & Ntow, 2009), a practice that further exacerbates the inability of farmers to read and understand pesticides labels. Many farmers seem to

8 be ignorant about the health implications of pesticides contamination. For instance, some apply pesticides without the required protective clothing whilst others use empty pesticides containers as drinking water bottles

(Ntow et al., 2009). The need for safer pest management options cannot be overemphasized.

Arrangements to integrate non-chemical pest management with chemicals at the governmental level started in the 1960s. This was an attempt to non- chemically manage the cocoa swollen shoot virus disease (Gerken et al.,

2001). Alternative pest control options have concentrated on using classical biological control methods. For instance, for the control of the cassava mealy bug, Phenacoccus manihoti (Hemiptera: Pseudococcidae) a parasitic wasp Epidinocarsis lopezi (Hymenoptera: Encyrtidae) was used (Korang-

Amoakoh et al., 1987). Integrated pest management was officially adopted as Ghana’s pest management strategy in 1992, and in 1995, the Ministry of

Food and Agriculture (MoFA) Ghana, and the FAO initiated a joint project with farmers and extensionists to promote IPM practices in rice, vegetables, cassava and plantain through Farmer Field Schools (FFS) (Gerken et al.,

2001).

Gerken et al. (2001) reported that the project had a positive impact and resulted in a 30% increase in income and a 90% reduction in pesticide use by participating farmers. Impact assessment of the IPM programme reported by Afreh-Nuamah (2003) also showed that crop yields rose by 150% whilst crop losses dropped from 46.2 % to 10.4%. Similarly, production costs of farmers in the IPM programme reduced by about 40 to 58%. Vegetable farmers reported of high quality, damage-free and tastier produce with

9 longer shelf life compared to that from the normal farming practices (Afreh-

Nuamah, 2003).

The choice of pest management option and the type of pesticide to be applied in Ghana largely depends on the type of crop involved (Blay et al.,

2000). Whilst 90% of farmers who grow starchy food crops such as cassava, plantain, yam and cocoyam do not apply pesticides, about 56% of those who grow cereals apply pesticides both in the field and during storage (Gerken et al., 2001). The figure may be higher for farmers who cultivate vegetables with a higher pest load such as cabbage.

1.3 The status of the use of botanical insecticides in Ghana

Traditional pest management with products such as vegetable oils, wood ash, neem extracts and other botanical mixtures have been well known to farmers in Ghana especially for the control of storage pests of cereals and legumes (Belmain et al., 2001; Gerken et al., 2001). A survey conducted by

Gerken et al. (2001) showed that between 14% and 25% of farmers in

Ghana, depending on the size of their farms, were found to use various traditional products for crop protection. Botanical insecticides have enjoyed successes in Ghana but mostly in the storage of cereals and grains (Belmain

& Stevenson, 2001).

Plants that have been used as botanicals in Ghana include; Azadirachta indica, Cassia sophera (Fabales: Fabaceae), Chamaecrista nigricens

(Fabaceae), Cymbopogon schoenanthus (Poales: Poaceae), Lippia multiflora

(Verbenaceae), Ocimum americanum (Lamiales: Lamiaceae), Securidaca longepedunculata (Polygalaceae), Synedrella nodiflora (Asterales:

Asteraceae) (Belmain et al., 2001). Other plants such as Chromolaena odorata (Asterales: Asteraceae) (Owusu, 2000), Capsicum frutescens,

(Solanales: Solanaceae) (chilli pepper) and garlic (Mochiah et al., 2011b) have been used for pest management in Ghana. However, aqueous neem extract and neem oil have been the most frequently used and have been successful in managing insect pests of cabbage, tomatoes, cowpeas, African egg plant and okra in Ghana (Obeng-Ofori & Ankrah, 2002; Appiagyei,

2010; Mochiah et al., 2011b). In recent times garlic and hot pepper have been used to successfully managed P. xylostella and other field pests of cabbage and results compare favourably against synthetic insecticides such as emamectin benzoate and even better than Lambda-cyhalothrin (Fening et al., 2011). Mochiah et al. (2011b) used commercial extract of garlic, Garlic

Barrier® to manage pests on African eggplant. Other botanicals such as the leaves of papaya were used to manage pests such as aphids, cotton stainers, white flies, flea beetles (Mochiah et al., 2011b). This botanical insecticide did not have any negative impact on non target organisms (Mochiah et al.,

2011b), thus making it ideal in an IPM programmes (Buss & Park-Brown,

2002).

Whilst efforts are being made to get some botanical insecticides registered in North America, Europe and other developed nations (Isman, 2008) to allow their use, in some developing countries such as Ghana, the legal framework regulating the use of botanical insecticides is not available

(Edmund, 2005). This means farmers can use botanical insecticides for domestic food crops production. Isman (2008) pointed out that whilst it appears irrational to be interested in using crop protectants that do not have

11 legislative approval due to health concerns, available evidence suggests that plant-based insecticides at worst are safer to human health than conventional insecticides.

1.4 Prospect for wider use of botanical insecticides in Ghana

Farmers in Ghana rely on synthetic insecticides for insect pest management irrespective of the crop involved (Ntow et al., 2006; Essumang et al., 2008;

Armah, 2011; Bempah et al., 2011). It is worth noting that over reliance on synthetic insecticides by Ghanaian farmers is not a matter of choice, but the only option available (Gerken et al., 2001). Greater number of farmers are willing and would avoid synthetic insecticides if there are reliable and safer alternatives (Coulibaly et al., 2007). It was revealed through interaction with farmers at Akomadan, a tomato growing community in the Ashanti region of Ghana that, due to the over reliance on synthetic insecticides, many of them do not consume vegetables from their own farms (B. Amoabeng, personal observation).

Studies have confirmed that, Ghanaians, irrespective of their financial status, are willing to pay premium prices for food commodities without pesticide contamination (Coulibaly et al., 2007; Probst et al., 2010). In a survey to find out the perception of potential vegetables buyers in Kumasi and Accra (the two most populous cities in Ghana) Probst et al. (2010) found that consumers will buy vegetables that are certified as free from pesticide contamination without considering factors such as price, sizes and shapes of vegetables and distance from their homes to the market where pesticide-free vegetables are sold. Undoubtedly, organic farmers, and more

12 especially vegetable growers will take advantage of the potential market for organic produce and shape their pest management tactics to suit consumers’ preference if reliable alternatives to synthetic insecticides are more available.

Already, the perception of pesticide contamination of vegetables and other food commodities has spread throughout Ghana. This has resulted in some consumers distancing themselves from buying and consuming fresh vegetables such as cabbage, lettuce, tomatoes that are mostly eaten raw or partially cooked. A study evaluating pesticide residues in cabbage at the farm gate in Cape Coat, Central region of Ghana, Armah, (2011) detected residues of 21 insecticides, of which nine (allenthrin, bifenthrin, lamda- cyhalothrin, fenvalerate 2, cyfluthrin 3, cypermethrin, cypermethrin 2, permethrin and deltamethrin) were pyrethroids whilst 12 (diazinon, fenitrothion, ethoprophos, chlorpyrifos, phorate, fonofos, frimidophos-m, profenofos, malathion, dimethoate, chlorfenvinpos and parathion-et) were organophosphates. Most of the chemical contaminations were above the maximum residue limit (MRL). Another study conducted by (Darko &

Akoto, 2008) confirmed the perception that some vegetables on the

Ghanaian market are contaminated with pesticides. In that study, contamination of tomato, African eggplant and chili pepper with organophosphates was assessed in the Kumasi central market. The study concluded that, life time consumption of tomato and eggplant from that market pose health risk due to the levels of pesticide residues. Some pesticides that were detected in the samples include ethyl-chlorpyrifos,

13 methyl-chlorpyrifos, dichlorvos, malathion, monocrotophos and methyl- parathion.

1.5 General overview of cabbage production in Ghana

Cabbage is a temperate crop but it is well adapted in Ghana’s climate

(Timbilla & Nyarko, 2006). The crop is cultivated throughout the country both on a small and large scale basis (Timbilla & Nyarko, 2006; Asare-

Bediako et al., 2010; Mochiah et al., 2011a). Even though cabbage is grown throughout the country, intensive, all year round cultivation usually occurs at lowland and marshy areas in and around the cities to take advantage of the high demand for the vegetable (Grzywacz et al., 2010; Mochiah et al.,

2011a). Unlike some other exotic vegetables in Ghana such as lettuce, cauliflower, cucumber, spring onion and carrot whose patronage is perceived to be wealth dependent, cabbage enjoys fairly reasonable consumption by all (Probst et al., 2010; Mochiah et al., 2011a).

Cabbage production occurs throughout the year in Ghana. Inadequate rainfall during the dry season (December-March) limits production to areas with perennial water supply. This usually leads to reduction in supply resulting in escalating prices in dry season and onset of the rainy season.

According to Timbilla & Nyarko (2006) about eight varieties of cabbage are cultivated in the country but currently, the most widely cultivated variety is cv. Oxylus (Mochiah et al., 2011a). In Ghana, cabbage is grown as a monocrop usually in a rotation system with other vegetables such as lettuce, cucumber, sweet pepper and spring onion. However, it is not uncommon to see the crop being grown continuously on a piece of land for several

14 seasons; a system that encourages a buildup of pests. Soil nutrition is usually improved by the application of poultry manure.

Insect attack is the most serious constraint to cabbage production in the country (Obeng-Ofori & Ankrah, 2002; Grzywacz et al., 2010; Mochiah et al., 2011a). The pests in Ghana include; DBM, cabbage aphid, cabbage web worm, cabbage looper, imported cabbage worm, the whitefly, cutworm

(Fening et al., 2011; Mochiah et al., 2011a). A survey conducted by

Timbilla & Nyarko (2006) showed that 80% of crop protectants used in managing pests of cabbage were synthetic insecticides but DBM had apparently become resistant to all available synthetic insecticides in the country by 1990. According to that survey, 20 chemical insecticides were used in cabbage production in the country though most of them were not recommended. Other constrains to cabbage production in the country include diseases, inadequate water supply during dry season, poor market for the produce during oversupply, land acquisition, lack of storage and credit facilities (Timbilla & Nyarko, 2006).

Table 1.1 Summary of major insect pests of cabbage in Ghana Name of pest Origin Distribution Estimated crop loss Biology Current management Scientific and common practices names Plutella xylostella Europe Worldwide Figures for Ghana are egg to adult 16- 23 days at Application of Diamondback moth not available but up to 25oC - 20oC insecticides but high 100% reported resistance is reported elsewhere Hellula undalis It was first Worldwide Not reported Eggs hatch between two to Carbaryl, Methomyl, Cabbage webworm identified in three days. About 25 days to Mevinphos. Italy complete life cycle

Trichoplusia ni North America Worldwide Not reported Eggs hatch in three to five Synthetic insecticides days. Caterpillars last for 14- are used but it is Cabbage looper 21 before pupating and pupal reported to have stage lasts for two weeks. developed resistance to some insecticides. Neem and other botanicals have been found to be effective.

Pieris rapae Europe, Asia Worldwide Not reported Eggs hatch in 8-10 days and Chemical control but its and Africa larvae go through 5 instar reported to have some Imported cabbage stages and take 15-18 days resistance against some worm/cabbage white for pupa to emerge chemical butterfly Botanicals could be applied

Agrotis spp. Not reported Worldwide Not reported A generation lasts for about These are sporadic pest two months. Eggs hatch in 6- and difficult to control. Cut worm 8 days and develop in 20-30 days.

Brevicoryne brassicae Europe Worldwide 10-90% loss reported Two forms of reproduction. Application of synthetic in India Sexless reproduction insecticides though Cabbage aphid resulting in live nymphs and some resistance have sexual that result in eggs that been reported are hatched.

1.6 Conclusion

To ensure food security, an important goal is to effectively manage pests.

Research has shown that, the increasing pest problems and the reported resistance of insects to insecticides are as a result attempts to completely eradicate insects. The outcome has been the numerous pesticide-poisonings, food contamination, eradication of beneficial organisms and the general destruction of the ecosystem.

Countries in the developing world are believed to be the worst offenders in the injudicious use of insecticides. For instance, research suggests that even though the use of pesticides in Ghana is not widespread compared to others countries, the intensity at which some farmers abuse insecticides is similar to countries where they are used extensively (Gerken et al., 2001).

Vegetables growers are among farmers in Ghana who use insecticides intensively. This has occurred because farmers do not get the needed motivation to adopt crop protection strategies that conform to sustainable agricultural practices. It is apparent that the focus and resources must be devoted to integrated pest management if sustainable pest management in

Ghana and other countries who share similar pest management problems will be achieved.

Botanicals are often regarded as safe to humans, animals and the environment because of their non-persistent nature (Dubey et al., 2011).

Some authors consider pest management with botanicals more expensive

(Buss & Park-Brown, 2002) compared to synthetic insecticides, others have contrary view (Belmain & Stevenson, 2001; Isman, 2008). Botanicals are

capable of managing insecticide-resistant pests of many crops. For botanicals to be widely accepted as crop protectants their ability to manage pest populations as well as their compatibility with other integrated pest management tactics in preserving natural enemy populations should be considered. They should also be a cost-effective alternative to synthetic insecticides in pest management.

In many tropical countries including Ghana, several plant species with activity against pests are known to farmers and are readily available for use.

Often most of these plant species are weeds, shrubs and trees that are weeds in crops and farmlands. If efforts are made to extract potent compounds from such common plant material by resource-limited farmers in the developing world, they can manage pests on their crops with little effort.

This would reduce the numerous problems encountered by farmers who use synthetic insecticides.

1.7 Thesis aim and objectives

The main aim of this research was to evaluate the potential of selected plants with activity against insects in managing pests of cabbage in the

Ashanti region of Ghana. The overarching hypothesis was that, the selected insecticidal plants could cost-effectively manage insect pests of cabbage, produce high quality cabbage head yield and preserve natural enemies of cabbage pests.

Specifically, this thesis had the following objectives:

19 i. to conduct cage plant tests to identify the activity of extracts

from shortlisted plant species against P. xylostella and B.

brassicae; ii. to conduct field evaluations to determine the practicability and

efficacy of plant extracts in managing insect pests of cabbage

and to provide information on the effect of the botanicals on

beneficial arthropods; iii. to conduct economic analysis of using botanical and synthetic

insecticides.

Chapter two

2.1 Literature review

2.2 The need for safer pest management options

Farmers and consumers have recognised the harmful effects of chemical insecticides, however, these pesticides will continue to provide the major means of controlling pests (Isman, 2008). Agrochemical companies have been able to reduce the harmful effects of synthetic insecticides in their newer products, but public perception to synthetic insecticides remain largely negative due to the legacy of insecticides such as the DDT (Isman,

2008). This has aroused interest in the use safer pest management options such as botanicals. Botanicals may once again gain popularity especially in situations where human exposures and health concerns are a priority (Isman,

2008; Regnault-Roger & Philogène, 2008).

Approximately three million agricultural workers are poisoned with pesticides globally each year, and some 20, 000 deaths can be directly linked to agrochemical use (Dinham, 1993; Koul et al., 2004; Darko &

Akoto, 2008). Nearly 100% of sampled human population was found to contain residues of pesticides such as the DDT (Dhaliwal & Arora, 2002;

Koul et al., 2004). In a developing country such as India, large proportion of food commodities sampled was found to contain pesticide residue above the maximum residue limit (Koul et al., 2004). Koul et al. (2004) reported that, only a small portion (less than 1%) of pesticides applied to protect crops reaches the target pests, the remaining (greater than 99%) find its way to other parts of the environment to contaminate soil, water, air, food, feed, forages and other commodities.

2.3 Botanical insecticides

Extracts and essential oils of certain plants have been used to protect crops against attack for ages because they have proved toxic to some economic important insect pests (Belmain & Stevenson, 2001; Isman, 2000, 2008).

Botanical insecticides in pest management were relegated to the background with the introduction of the quick acting, relatively efficacious but generally hazardous synthetic insecticides (Isman, 2008). Isman (1997) reported that in the year 1947 about 6700 tons of Derris elliptica (Fabales: Fabaceae) roots (a source of rotenone; a strong botanical insecticide) were imported from Southeast Asia to the USA. However, the introduction of organochlorine and organophosphates caused a sharp decline in the import of D. elliptica to 1500 tons by the year 1963.

2.4 A brief history about botanical insecticides

Botanical insecticides date back to 1200 BC, when the pesticidal properties of plants were exploited for seed treatments in China (Koul et al., 2004;

Uneke, 2007). Botanical insecticides such as pyrethrum and derris were discovered and widely traded internationally between the years of 1750 and

1880 (Isman, 1997). Soloway (1976), Rosell et al. (2008) and Isman (2006) confirmed that, botanical insecticides have been exploited for pest management over two millennia.

The advent of the synthetic insecticide dichlorodiphenyltrichloroethane

(DDT) in 1939 and the commercialization of other synthetic insecticides led to the demotion of botanical insecticides (Shanker & Solanki, 2000; Isman,

2006, 2008; Uneke, 2007; Rosell et al., 2008). In 1962, extract from the

Indian neem tree, Azadirachta indica (Sapindales: Meliaceae) was observed 22 to cause feeding deterrence against the desert locust, Schistocerca gregaria

(Orthoptera: Acrididae) (Koul, 2004). Nearly 900 compounds have been found to possess a feeding deterrence against insects (Koul, 2004). Plants possess a wide range of secondary metabolites, likely over 100,000 unique compounds and each is believed to have deterrence against some insects

(Koul, 2004). Presently, botanical insecticides in commercial use fall into four major types; pyrethrum, rotenone, neem and essential oils, whilst ryania, nicotine and sabadilla are in limited use (Koul, 2004; Rosell et al.,

2008).

2.5 Active compounds in botanical insecticides

Phytochemicals (secondary metabolites) are compounds that are naturally occurring in plants. They are responsible for imparting organoleptic characteristics such as colour and smell. Plant secondary metabolites include chromenes, cuccurbittacins, glucosides, quassanoids, saponins, tannins, polyacetlylenes, cyclopropanoidacids, essential oils, organic acids, flavonoids, alkaloids, phenolic compounds and terpenoids. The most potent antifeedants are found in the terpenoids; precisely the triterpenoids (Isman,

2002). The occurrence of secondary metabolites varies between parts of plants taken and can be specific to families, subfamilies, and subspecies

(Balandrin et al., 1985; Koul, 2004).

Plant allelochemicals have diverse effect on insects (Isman, 2002; Koul,

2004; Regnault-Roger & Philogène, 2008). These compounds are classified according to their modes of action that protect plants from excessive insect herbivory (Isman, 2002; Regnault-Roger et al., 2005; Regnault-Roger &

Philogène, 2008). They include toxicity, repellency, antifeedant, oviposition deterrence, digestion inhibition, attractant, impairing larval growth (Isman,

2002; Koul, 2004; Regnault-Roger et al., 2005). Allelochemicals are selective in their action. An allelochemical from one source may not have the same effect on different stages of an insect. Thus, insects sensitivity to an allelochemical changes depending on their physiological development

(Regnault-Roger et al., 2005). This selectivity facilitates plants secondary metabolites to act on the target insect species at specific developmental stages (Demolin et al., 2002; Koul, 2004). Combining plants with different insecticidal properties creates a unique allelochemical that results in synergy among the different plant secondary metabolites to reduce the development of pest resistance (Demolin et al., 2002).

2.6 Modes of action of botanical insecticides

Overall, attention and more studies have been concentrated on antifeedant effect of allelochemicals than on the other modes of action (Koul, 2004;

Regnault-Roger et al., 2005). Antifeedant substances, however, may show other biological effects such as toxicity, oviposition deterrence and reduced fertility of surviving insects (Koul, 2004). Antifeedants are “behaviour modifying substances that deter feeding through a direct action on peripheral sensilla” (Isman, 2002; Koul, 2004). This definition does not include actions that suppress feeding by acting on the central nervous system or substances that have sublethal toxicity to insects (Isman, 2002;

Koul, 2004). Feeding deterrence with diverse structures are known to directly interfere with insects taste cells response to phagostimulants such

24 as sugars, but the mode of action of feeding modifying chemicals in insects gustatory system is not known (Koul, 2004).

Extracts or crude forms of numerous plants can have a feeding deterrence action against several insect pests of economic importance. According to one study, a 10% leaf and 4% seed extract of A. indica, gave a high feeding inhibition against the caterpillar of Achoea janata (Lepidoptera: Noctuidae) and B. brassicae respectively (Ignacimuthu, 2005). Similarly, extracts of

Melia azaderachta and Annona squamosa showed strong feeding deterrence against pests such as beetles, defoliators and sap sucking insects. Other plants such as the Ricinus communis (Malpighiales: Euphorbiaceae)

Malpighiales: Euphorbiaceae) and Murayya sp (Sapindales: Rutaceae) are known to possess certain alkaloids that are insect feeding-deterrents

(Ignacimuthu, 2005).

Botanical insecticides that are oviposition-deterrent will reduce the potential number of eggs that would have been laid (Ignacimuthu, 2005). Precocene I and II, are active components in Ageratum conyzoides (Asterales:

Asteraceae) and have been found to be insects oviposition-deterrents

(Borthakur et al., 1987). Several other plants exhibit oviposition deterrence in addition to other modes of action such as ovicidal activity (Ignacimuthu,

2005). Crude leaf extract of Tephrosia sp resulted in significantly better oviposition deterrence when applied against the Mexican bean beetle,

Epilachna varivestis (Coleoptera: Coccinellidae) on the bitter gourd,

Momordica charantia (Cucurbitales: Cucurbitaceae) than Diazinon 60 EC at

2 mL/L of water in Bangladesh (Rahaman et al., 2008). Upasani et al.

(2003) reported that, flavonoids in the aqueous leave extract of R. communis had excellent oviposition deterrence against Callosobruchus chinensis

(Coleoptera: Chrysomelidae).

Some plants also have toxic secondary metabolites and application of an extract can result in acute mortality of certain insect pests. The alkaloid nicotine found in Nicotiana spp. (Solanales: Solanaceae) has been found to exhibit acute toxicity in several insect species (Tiwari et al., 1995). It is believed to be the most toxic of all botanical insecticides and could cause harm even to humans if care is not taken during handling and application

(Rosell et al., 2008). The high content of rotenoids in plants such as the

Tephrosia sp also imparts high toxicity to the plant extracts. The seeds of R. communis are reported to be highly toxic due to the presence of proteins that exhibit cytotoxic and heme-agglutinating characteristics (Elimam et al.,

2009).

Botanicals such as Ocimum spp. (Lamiales: Lamiaceae) and Synedralla nodiflora (Asterales: Asteraceae) cause repellence (Belmain & Stevenson,

2001; Kéita et al., 2001) as well as an anti-juvenile hormone as exhibited in

A. conyzoides (Borthakur et al., 1987). It is, however, worth noting that most of these botanicals combine more than one mode of action to achieve their pest control; a characteristic that makes botanical insecticides a suitable choice in terms of reducing insect resistance through the synergy among the various components (Koul, 2004). Based on the dosage and age of exposure to botanicals, an insect may experience premature death or prolonged larval period coupled with morphological abnormalities

(Ignacimuthu, 2005). Inhibition of molting in Rhodinus prolixus

(Hemiptera: Reduviidae) due to the application of azaderachtin, metamorphosis (Mochiah et al., 2011b) inhibition of the red cotton bug,

Dysdercus koenigi (Heteroptera: Pyrrhocoridae) due to the application of

Cedrus deodara (Pinales: Pinaceae) and production of non-viable adults due to deformed wings and shrunken abdomen due to the presence of anti- juvenile hormones in such botanicals have been reported (Ignacimuthu,

2005).

2.7 Advantages and disadvantages of botanical insecticides

Botanical insecticides can provide realistic alternatives to chemical insecticides because of their safety to the user and the wider ecosystem

(Rechcigl & Rechcigl, 2000; Buss & Park-Brown, 2002). They are selective in nature (Ignacimuthu, 2005), perform specific actions on the target pest, and do not frequently result in pesticidal resistance (Isman, 2002; Koul,

2004; Regnault-Roger et al., 2005; Charleston et al., 2006). Besides the insecticidal activities of secondary metabolites, botanicals can exhibit action against plant pathogens such as fungi. Unlike synthetic insecticides, botanical insecticides are natural and easily degradable in the eco-system upon exposure to sunlight, air and moisture (Buss & Park-Brown, 2002;

Dubey et al., 2011).

Even though very recent figures are not available, according to Isman

(2005) and Koul (2004), growth in annual sales of between 10-15% may be realised for botanicals. Only about 10% of plant species have been exploited for their bioactive compounds, so there are opportunities for discovering more efficacious insecticidal compounds in the nearly 90% of the

27 unexploited plant species (Uneke, 2007). There is growing demand for food without synthetic pesticide contamination, and organically produced foods are attracting premium prices (Njoroge & Manu, 1999). In many places of the world, botanicals are accepted as crop protectants in organic food production. If the trend of preference to organic foods is sustained, many farmers will be persuaded to use botanicals.

Botanical insecticides are known to work synergistically such that the combined efficacy of two or more compounds is higher than that of single compound. For example, the growth inhibitory effect of refined bark extract of Melia toosendan (Sapindales: Meliaceae) containing 60-75% toosendanin was significantly greater than that of pure toosendan (Isman, 1997) an indication that lesser constituents were making overall bioactivity greater than expected based on their mass (Isman, 1997). Even though some synthetic insecticides can exhibit additive effects, many others are reported to be antagonistic when combined (Ahmad et al., 2009b).

Botanicals are gaining acceptance where chemical pesticide residues are least tolerated. In the richer countries botanicals will be embraced in controlling domestic pests such as flies, cockroaches and those that infest pets (Isman et al., 2011). In this respect, the safety of the products to humans, animals and the environment (as exhibited by botanicals) (Isman,

2008; Dubey et al., 2011) is more important than its rapid, knock-down effect; the latter being a common attribute of synthetic insecticides. Already the Environmental Protection Agency’s (EPA) USA, has exempted certain

28 plant based essential oils from registration and other countries such as Japan and Korea may follow (Isman, 2008).

The advantages of botanical insecticides in pest management abound in the poorer countries where most the farmers have limited resources and cannot afford synthetic insecticides even more than their wealthier counterparts

(Lehman et al., 2007). In many developing countries including Ghana, botanicals are exempted from pesticides registration as there are no legal frameworks regarding the use of biopesticides. Indigenous farmers in some tropical countries have exploited plant extracts in managing insect pests in the field and in storage (Belmain & Stevenson, 2001; Lehman et al., 2007).

Isman (2008) reported that, when synthetic pesticides became unavailable to farmers for economic reasons, cocoa farmers in Cameroon turned to extracts of local plants either alone or mixed with synthetic insecticides in managing pest on their farms. As a result, the percentage of farmers growing cocoa without synthetic pesticides rose from 6 to 33 (Isman, 2008).

Embracing botanical insecticides allow resource-poor farmers in developing countries to obtain income by participating in the cultivation and extraction of these plant-based insecticides (Isman, 2008). An added advantage of growing insecticidal plants such as those in the Fabaceae family would be the improvement of the physical properties and fertility of their soil through atmospheric nitrogen fixation by the plants and reducing the need for fertilisers.

Further, shifting from the use of synthetic insecticides to botanicals and for that matter organic vegetable production will enhance the livelihood of the resource-limited farmer in poor countries in the world through selling of produce for premium prices. According to Coulibaly et al. (2007) consumers in Ghana and Benin are willing to pay more than 50% extra as price premium for vegetables that are free from potential chemical contamination. By using plant materials to manage insect pests, farmers from poorer countries may have better opportunity to access the European

Union and the US markets and obtain higher prices for their commodities

(Njoroge & Manu, 1999). Organic farming has great potential in Africa as agriculture is already de-facto organic in many countries. This is evident from the fact that African agriculture is characterised by low level of input use and the low take-up of green revolution technologies (Parrot et al.,

2009).

In many developing countries, majority of those who handle insecticides are illiterate or read only their local language whilst pesticide labels are written in foreign languages such as English, French and Chinese (Isman,

2008). The introduction of botanicals in IPM systems will reduce the rate of pesticidal poisoning in these areas.

Despite the numerous advantages botanical insecticides have, there are challenges that must be overcome if their full potential is to be realised in both small scale and large scale crop protection. Botanical insecticides often have complex chemical composition and can have different molecular and biochemical targets on insects, but repeated and inappropriate use result in

30 insect resistance just as with synthetic insecticides (Koul, 2004; Regnault-

Roger et al., 2005). Another limitation of botanical insecticides, especially of the antifeedants reported by Koul (2004) is that, insects can become habituated upon continuous exposure. That means, the botanical can offer protection to the crop or produce for a limited period and the insects will overcome the efficacy of the protectant. This however, can potentially be overcome by mixing two or more botanicals before application (Koul,

2004).

Botanicals are relatively slow in their action compared to synthetic insecticides (Buss & Park-Brown, 2002) and are not suitable in situations of high pest infestations where rapid control action is required. Botanical insecticides are more likely applied as barriers with modes of action such as repellence, oviposition deterrence, and antifeeding actions instead of acute toxicity (Isman et al., 2011). Other limitations such as varying efficacy, poor persistence and inconsistent availability of insecticidal plants may limit the potential of botanical insecticides (Koul, 2004; Isman, 2005). By planting insecticidal plants that are not abundant, the problem of inconsistent availability especially for commercial extraction will be overcome.

2.8 Extraction and purification of plants’ secondary metabolites

Extraction of botanical components can be done when plant material is either fresh or dried. When dried plant materials are being used, drying should be controlled to minimise chemical changes (Harborne, 1998;

Letellier & Budzinski, 1999). Analysis of plant constituents such as flavonoids, alkaloids, terpenoids and quinines have been done successfully

31 on herbarium plant materials that have been stored for several years

(Harborne, 1998).

According to Harborne (1998) an important precaution to take in plant constituent analysis is to avoid contamination of the desirable plant material with foreign ones. Two closely related plant species could be mixed, and that will potentially alter the result of the analysis. The species should therefore be authenticated by a trusted authority to avoid using the wrong or mixed material. Additionally, it is important to observe that plant materials are free from fungal, viral and other pathogenic contaminations.

The precise extraction technique to employ for the phytochemical analysis is dependent on the texture and water content of the plant material and on the substance that is to be isolated (Harborne, 1998). Alcohol is a good all- purpose solvent in extraction (Harborne, 1998). Other considerations to make in selecting an extraction technique are amount of solvent that will be used and the duration of extraction (Letellier & Budzinski, 1999).

Though methods of extraction such as the Soxhlet extraction, microwave- assisted extraction (MAE) and chromatographic methods are available, depending on the locality and the type of plant material to be used, extraction could be done by using simple techniques such boiling the plant material and using the water with the diffused phytochemicals for spraying or application. Pounding of material in wooden mortar using wooden pestle before mixing the pulp with water is also used by some farmers. These

32 plants are indigenous and sometimes weeds obtained without cost (Rathi &

Gopalakrishnan, 2006; Owolabi et al., 2010).

2.9 Parts of plants used as botanical insecticides

Every part of a plant is a potential source of secondary metabolites with insecticidal activity. However, every insecticidal plant may have a part where component responsible for the insecticidal activity is concentrated most. For instance, in A. indica, leaves and seeds are often used (Charleston et al., 2006) whilst in R. communis leaves can be used but the seeds have been found to produce the highest insecticidal activity (Upasani et al.,

2003). On the other hand, in Tephrosia spp., rotenone responsible for their insecticidal power is concentrated highest in the roots (Koona et al., 2007).

Selecting plant parts for use as botanical insecticide should be based on previous studies or by testing the various parts to determine the most active part. Consideration should be given to the ease of extraction. Tree barks of certain insecticidal plants such as the African mahogany, Khaya spp.

(Meliaceae) may contain better insecticidal properties than the leaves but it may be practically difficult to prepare extracts from the bark, in which case, the leaves may be used.

Ground materials are usually extracted in solvents such as water, ethanol, and methanol after which the mixture is sieved (de Oliveira et al., 2011).

There are several reports on the use of crude extracts of plants in managing both field and storage insect pests of crops. Moreira et al. (2007a) used crude extract of A. conyzoides to control Rhyzopertha dominica (Coleoptera:

Bostrichidae). Belmain & Stevenson (2001) exploited crude extracts of

33 several plant materials in Ghana to manage storage pests of grains and legumes with significant success. de Cássia Seffrin et al. (2010) reported on the control of the cabbage looper, T. ni using crude aqueous extract of

Annona squamosa and Annona atemoya (Magnoliales: Annonaceae) and several successes with crude extracts.

2.10 Management of cabbage pest with botanicals

There is need to explore the possibilities of obtaining more potent extracts from the relatively unknown sources. Preferably, farmers will resort to plant species that are available in their vicinity and on their farmlands to manage pests if their efficacy is proven. Other plant species have been used successfully to manage pests of storage products and other field pests mostly lepidopterans other than those of cabbage.

2.11 Insecticidal plants used in this study

2.11.1 Ageratum conyzoides (Asterales: Asteraceae) goat weed

Ageratum conyzoides an erect, annual herbaceous plant is believed to be native to tropical America, and has long history of use in traditional medicine (Moreira et al., 2007a). Ageratum conyzoides isvery common in

West Africa, Australia, Asia and some parts of South America (Kamboj &

Saluja, 2008). It has an odour similar to that of a male goat, hence the common name billy goat weed (Okunade, 2002). The plant is believed to have phytochemical properties capable of healing burns and wounds, microbial infections, infectious conditions, bacterial infections, arthrosis, headaches, dyspnea, pneumonia, and analgesic, anti-inflammatory, antiasthmatic, antispasmodic and haemostatic effects, stomach ailments, 34 gynecological diseases, leprosy and other skin diseases (Kamboj & Saluja,

2008).

Variability in secondary metabolities exists between populations of A. conyzoides that include flavonoids, alkaloids, cumarins, essential oils, tannins, triterpene and sterols. Essential oil yields of 0.02% to 0.16% may be obtained from the plant (Siqueira-Jaccoud, 1961). Kamboj & Saluja

(2008) also reported an essential oil yield of 0.11 to 0.58% from the leaves and 0.03 to 0.18% from the roots. Analyses of the essential oil showed 213 compounds of which about 51 have been identified. These include 20 monoterpenes, 13 monoterpenoid hydrocarbons, 7 oxygenated monoterpenoids, 20 sequiterpenes, 16 sesquiterpenoid hydrocarbons, 4 oxygenated sesquiterpenoids, 3 phenylpropanoids and benzenoids. 7- methoxy-2, 2-dimethylchromene (precocene I) and 6,7-dimethoxy-2,2- dimethylchromene derivative, ageratochromene (precocene II) are largely the main component of the essential oil (Kamboj & Saluja, 2008). Research by other people showed similar results. For instance, Borthakur et al. (1987) identified precocene I and precocene II, in a sample collected from India.

Ekundayo et al. (2007) identified 51 terpenoid compounds, including precocene I and precocene II. Mensah et al. (1993) reported similar yields of precocene I and II in the essential oil of A. conyzoides collected from

Ghana. Precocene I and precocene II are the compounds responsible for the insecticidal activities of A. conyzoides (Rathi & Gopalakrishnan, 2006).

Ageratum conyzoides has bioactivity that is useful in agriculture in particular insect pest management (Okunade, 2002). It has insecticidal activities against wide range of insect pests (Rathi & Gopalakrishnan,

2006). Precocene I and II are reported to be an anti-juvenile hormone, 35 oviposition deterrent (Borthakur et al., 1987) and have acute toxicity against insects when used as fumigant, for example, against Callosobruchus maculatus (Coleoptera: Bruchiddae) (Kamboj & Saluja, 2008). Nymphal mortality of 91% was observed in the desert locust, Schistocerca gregaria

(Orthoptera: Acrididae) upon application of A. conyzoides oil (Okunade,

2002). Methanolic extract of the leaves at 250 and 500ppm exhibited absence of juvenile hormone in the fourth instar of Chilo partellus

(Lepidoptera, Pyralidae), a sorghum pest (Okunade, 2002). An extract from the plant is reported to induce morphogenetic abnormalities in mosquito larvae of Culex quinquefasciatus, Aedes aegypti, and Anopheles stephensi

(Diptera: Culicidae) (Ming, 1999). Anti-juvenile hormone activity by precocenes I and II has been shown on a range of insects including

Sitophilus oryzae (Coleoptera: Curculionidae), Thlaspida japonica,

Leptocarsia chinesis and Dysdercus flaidus (Okunade, 2002). According to that study, this leads to the production of precocious metamorphosis of the larvae and production of sterile, moribund and dwarfish adults.

In a laboratory experiment with maize weevil, Sitophilus zeamais

(Coleoptera: Motschulsky) in Cameroon, Bouda et al. (2001) reported 100% mortality of the test insect to A. conyzoides at essential oil concentrations between 0.063-0.5 % within 24 hours of exposure. About five times reduction in the concentrations to 0.013, 0.025, 0.05, and 0.1% w/w also showed 100% mortality, though this occurred after 96 hours of exposure

(Bouda et al., 2001). Whilst results from various experiments have generally been positive irrespective of the solvent used in extraction, Moreira et al.

(2007a) reported that only hexane extract of A. conyzoides caused 76%

36 mortality to Rhyzopertha dominica (Coleoptera: Bostrichidae) whilst extract using other solvents did not give significant control. Koul (2008) reported that 43.0–68.75% mortality in Spodoptera litura was observed when essential oil of A. conyzoides at 0.025–0.25 μl concentration was applied.

Although the precocenes have been seen as excellent fourth-generation insecticides, the negative aspect is that, they have been shown to cause hepatotoxicity in rats (Okunade, 2002). This becomes important considering human health hazard in large scale field applications. It is evident from the works of previous authors that secondary metabolites of A. conyzoides have generally being used against insect pests of stored products especially those in the order Coleoptera. However, the anti-juvenile hormone, oviposition deterrence and acute toxicity exhibited by precocene I and II, and other secondary metabolites responsible for insecticidal activity of A. conyzoides, could be effective against other pests. Even though precocene is not water soluble, other secondary metabolites in the plant may be responsible for its insecticidal activity in water extracts. This plant is abundant in Ghana

(Table 2.1) and could be exploited for pest management since simple solvents such as water and ethanol for extraction (Bouda et al., 2001).

2.11.2 Chromolaena odorata (Asterales: Asteraceae) Siam weed.

Chromolaena odorata is believed to have originated in Mexico but it is now found in many parts of the tropics where it grows as weed (Owolabi et al., 2010). It has been used in West African traditional medicine as an antiseptic and in wound healing (Owolabi et al., 2010). Chromolaena

37 odorata is popularly called ‘Acheampong’ weed in Ghana probably because it became a problematic weed during the time of I. K. Acheampong as the head of state (Wadie James Fordjour, personal comm.). In remote areas of

Ghana where there is no access to mortuaries, C. odorata is used for embalming dead bodies.

Chromolaena odorata was first observed in Ghana in February 1969 at the

Legon Botanic gardens but by 1991, the extent of occurrence of the weed had extended to two-thirds of the total land area of the country (Timbilla et al., 1996; Timbilla & Braimah, 2002). Chromolaena odorata is reported to survive even under inadequate rainfall supply of less than 500mm per annum (Goodall & Erasmus, 1996). Although, C. odorata is claimed to have some useful attributes such as checking erosion, reducing fallow periods and improving soil fertility (Timbilla & Braimah, 2002), it is recognised as a weed in farmlands where the species smother food crops and native plants and is a threat to biodiversity as it spreads rapidly in the forest ecological zones (Castel, 2012).

Phytochemical analysis of the essential oil of C. odorata in Nigeria by

Owolabi et al. (2010) identified 56 compounds that represent 99.3% of the total oil content. Of this, α- and β-pinenes of 42.2% and 10.6%, respectively were found. Other compounds were, germacrene D 9.7%, β-copaene-4-α-ol

9.4%, (E)-caryophyllene 5.4%, geijerene 4.7% and pregeijerene, 2.8%.

According to that study, similar components were found in the earlier works by different authors in Ivory Coast and Thailand. Chromolaena odorata is also reported to possess coumarins, a component which might be

38 responsible for its insecticidal properties (Gutiérrez-Sánchez et al., 2009;

Moreira et al., 2007).

In Ghana, C. odorata has been used to control Tribolium castaneum

(Coleoptera: Tenebrionidae) and Sitophilus oryzae (Coleoptera:

Curculionidae) in rice (Owusu, 2000). In that study hexane + isopropyl alcohol (4 + 1 volume) extract of C. odorata leaves was used. Application rate was 10g of rice to 1g of plant extract. Survival rate of the test insects after 10 days of exposure reduced by 25% and 40% for T. castaneum and

S. oryzae respectively (Owusu, 2000). Dried leaf, water extract of C. odorata has also offered control of insects that transmit diseases to humans in Nigeria. In that study, the larvicidal properties of the plant was exploited against the black fly, Simuliu in comparison with chlorpyrifos (an organophosphate) at the rates of 0.01 mg/L, and 0.001 mg/mL) for C. odorata and chlorpyrifos respectively. Mortality of 100% was observed for all treatments (Matur & Davou, 2007). Chromolaena odorata has been used to manage Sitophilus zeamais (Coleoptera: Motschulsky) (Owolabi et al., 2010).

In another study in Nigeria, dried leaf powder of C. odorata was used to treat maize against S. zeamais in storage at the rates of 5, 10 and 15g C. odoratato 100g of maize. Percentage mortalities of 63.75, 70 and 75 were observed after 4 weeks. The result was comparable to that of Actellic® powder that gave 75.25% mortality at the rate of 0.04g over the same period

(Mbah & Okoronkwo, 2008). Chromolaena odorata can arguably be considered as the most abundant weed species in many parts of Ghana.

Exploiting its insecticidal activity will be a good step in putting the invasive weed to a good use. Extraction can be done with water (Adegbite &

Adesiyan, 2005), making it easy for smallholder farmers to use.

2.11.3 Synedrella nodiflora (Asterales: Asteraceae) Cinderella weed

Synedrella nodiflora is an annual weed and native to the tropical America

(Rathi & Gopalakrishnan, 2006). The plant has some medicinal properties.

In Ghana, infusion of the leaves is used to treat epilepsy and as a laxative. It has also been used to treat rheumatism and earache in Nigeria and some other countries (Bhogaonkar et al., 2011). Synedrella nodiflora is also reported to possess anti-fungal and anti-bacterial properties against organisms such as Aspergillus flavus, Candida albicans and Escherichia coli (Bhogaonkar et al., 2011).

Photochemical test of aerial parts of S. nodiflora collected from India showed the presence of steroids, phenolic compounds, saponins, tannins and reducing sugars (Rathi & Gopalakrishnan, 2006; Bhogaonkar et al., 2011).

However, differences could occur in the secondary metabolites depending on the solvent used. Whilst benzene and chloroform extracts showed the presence of steroids, methanol extract showed the presence of steroids, reducing sugars, phenolic compounds, saponins and tannins. Similarly, petroleum ether (40º - 60º C) produced steroids and triterpenoids whilst water extract showed the presence of reducing sugars, alkaloids, phenolic compounds, saponins, tannins and aromatic acids (Rathi & Gopalakrishnan,

2006). Synedrella nodiflora, like other members of the Asteraceae family is known to possess insecticidal properties against several species of insects

(Belmain et al., 2001). One hundred percent mortality of fourth instars of S. litura was observed when methanol extract of S. nodiflora was used whilst petroleum ether, benzene, chloroform and water extracts followed with 80,

75, 75 and 60% respectively (Rathi & Gopalakrishnan, 2006).

In another study, aerial parts of S. nodiflora were used against four storage pests of grains and legumes namely S. zeamais, C. maculatus, Rhyzopertha dominica and Prostephanus truncatus (Coleoptera: Bostrichidae). With the concentrations of 0.5, 1 and 5% of w/w, Belmain et al. (2001) found positive results against R. dominica and S. zeamais. They found that increased concentration and time of exposure were directly related to the degree of mortality. The study revealed that, S. nodiflora extract exhibited repellency against S. zeamais (Belmain et al., 2001). In a similar trial,

Belmain & Stevenson (2001) reported an excellent control of storage pests of grains by dipping grains in water in which leaves and flower heads of S. nodiflora had been boiled.

The ability of S. nodiflora to cause 100 % mortality in S. litura signifies its strong insecticidal potential (Rathi & Gopalakrishnan, 2006). In addition, since S. nodiflora was able to control S. litura, it may be able to control most of the serious lepidopteran pests of cabbage such as DBM, cabbage looper and web worm. Synedrella nodiflora is abundant in Ghana as common weed and can be obtained freely. Moreover, simple solvents including water can be used for the extraction of the secondary plant metabolites (Rathi & Gopalakrishnan, 2006).

2.11.4 Ocimum (Lamiales: Lamiaceae) basils

Ocimum are annuals or perennial shrubs that grow in several part of the world. Various species of the genus have been utilised to cure several ailments such as cough, fever, stomachache, and measles in several countries across Asia and Africa including Nigeria, Kenya, China and India

(Holm, 1999). Members of this genus have mixtures of terpenes, sesquiterpenes in their external and internal glands. The chemical composition is a function of species, chemotype, climate, soil conditions and geographical location (Ogendo et al., 2008). Analysis of the constituents of Ocimum kilimandscharicum and Ocimum kenyense in Kenya resulted in six major compounds in their essential oils; camphor, limonene, 4-terpeneol,

1,8-cineole, camphene and trans-caryophyllene (Bekele & Hassanali, 2001).

Kumbhar et al. (1999) and Ogendo et al. (2008) found that Z-β-ocimene and eugenol are the main components of the essential oil. Dambolena et al.

(2010) investigated the composition of the essential oils of Occimum basilicum and Ocimum gratissimum in Kenya and found that differences exist in chemical composition even among the same species collected from different geographical locations. The study found that leaves and flowers of

O. basilicum from Sagana area contained 95 % linalool which was the main component. However, flowering tops and leaves of the same species from another location; Yatta contained mainly 32.6 and 31.0 % camphor respectively. For O. gratissimum, it was established that, eugenol was the main constituent but showed slight differences in the amount of the component present at the two locations; 95.5 and 70.1 % for Sagana and

Yatta respectively and Z-β-ocimene (34.1 %) in the flowering tops

(Dambolena et al., 2010).

Many species of Ocimum posses insecticidal properties against several insect species that transmit diseases to humans as well as field crops and storage products (Holm, 1999; Kéita et al., 2001; Ogendo et al., 2008; Koul

& Walia, 2009). Koul et al. (2008) reported on the anti-feedant and larvicidal activity of Ocimum canum and O. sanctum against lepidopterans.

In assessing the efficacy of the essential oil and its constituents against storage pests of grains; S. zeamais and R. dominica, a dose of 1.44 mg per cm2 of filter paper of O. kilimandscharicum essential oil caused 100%

2 mortality of S. zeamais with LC50 of 0.76 mg per cm . For R. dominica, a

2 minimum dose of 0.8 mg per cm caused 100% mortality, with LC50 at 0.7 mg per cm2 (Bekele & Hassanali, 2001).

Ethanol extract of O. sanctum was used to control aphid species including

Myzus persicae, Metopolophium dirhodum, Aphis fabae, Sitobion avenae and Acyrthosiphon pisum (Hemiptera: Aphididae). The best result, however, was 79% mortality against M. dirhodum (Holm, 1999). Methanol extract of O. sanctum at 1% concentration, according to Holm (1999) gave

90% control of Henosepilachna vigintioctopunctata (Coleoptera:

Coccinellidae) after 12 to 24 hours of application. Kumbhar & Dewang

(1999) found that O. canum exhibited better repellence and insecticidal activity both and in combination with other plant materials. Mansour et al.

(1986) also found a repellence effect of acetone extract of O. basilicum against the carmine spider mite, Tetranychus cinnabarinus

(Trombidiformes: Tetranychidae). In a laboratory bioassay, O. basilicum exhibited both antifeedant and toxicity effect against the tobacco caterpillar,

S. litura and castor semilooper, Achaea janata, both lepidopterans

(Devanand & Rani, 2008).

Upasani et al. (2003) reported using constituents of Ocimum spp. in controlling Anopheles sp and Aedes aegypti in Nigeria and Brazil respectively. Ocimum santum was used to control fleas which are vectors of bubonic plaque, A. stephensi, A. aegypti and Culex quinquefasciatus

(Diptera: Culicidae) (Holm, 1999). Species of Ocimum have also exhibited control of lepidopterans such as A. janata and S. litura and thus have the potential of managing insect pests of cabbage which are predominantly lepidopterans (Devanand & Rani, 2008). Ocimum spp. are abundant in

Ghana as a medicinal plant and simple organic solvents could be used to extract the constituents. Water and ethanol in the ratio of 1:1 was successfully used for extraction (Senthilkumar et al., 2009).

2.11.5 Nicotiana tabacum (Solanales: Solanaceae) tobacco

The exact origin of N. tabacum is not clear as the plant is believed to have resulted from chromosome doubling following the hybridisation of

Nicotiana sylvestris (Gray et al., 1974). Nicotine is the main alkaloid that is found in the tobacco plants, N. tabacum and N. rustica, and it is the most toxic botanical insecticide with LD50 of 50mg/kg in rats and harmful to humans as well if absorbed through the skin (Rosell et al., 2008). Nicotine, owing to its extreme toxicity to mammals and its rapid dermal absorption in humans has lost its regulatory approval as an insecticide in many countries

(Akhtar et al., 2008). Plant alkaloids in tobacco are reported to cause changes in the physiological functions of several insects (Tiwari et al.,

1995). Efficacy of tobacco has been tested against several insect pests with high rates of successes. Rosell et al., (2008) described the insecticidal activity of tobacco as outstanding among other botanical insecticides.

Apart from the alkaloids, commercial tobacco is reported to have other constituents such as nor-nicotine, anabasine and other alkaloid-related substances (Rosell et al., 2008). The mode of action of insecticidal compounds in N. tabacum has been described as a contact. It acts at the acetylcholine receptor which leads to uncontrolled firing of the neuroreceptor as observed in organophosphates and carbamates (Rosell et al., 2008). Hundred percent mortality was achieved when N. tabacum was tested against the Colorado potato beetle, Leptinotarsa decemlineata

(Coleoptera: Chrysomelidae) which is known to be resistant to several synthetic insecticides (Tiwari et al., 1995). Nicotine is also reported to be the most effective botanical insecticide against soft-bodied insects and mites such as aphids, thrips, leafhoppers and spider mites (Rosell et al., 2008).

In testing the insecticidal activities of some African plants against the bean weevil, C. maculatus on cowpea in Benin, Boeke et al. (2004) reported that, the powder of N. tabacum was not the best in repelling the test insects, but its complete ovicidal effect adds to the overall efficacy. According to that study, N. tabacum caused no significant reduction in the total number of eggs laid but there was complete cessation of egg development preventing larvae from penetrating the beans. There are, however, other conflicting

45 reports on the activity of N. tabacum against insects. For instance, Ofuya

(1990) reported that total eggs laid and hatched on beans treated with N. tabacum powder were lower than the other treatments. Boeke et al. (2004) reported on an earlier study that used N. tabacum to control cowpea weevil.

In that report, N. tabacum did not result in any effective control of bruchid beetles. Egg mortality, according to the report was lower on N. tabacum treated beans than any of the other treatments applied. Culex quinquefasciatus was successfully controlled with hot water, acetone, chloroform and methanol extracts of N. tabacum. In that study, 100% larval mortality of C. quinquefasciatus was observed for all the extracts of N. tabacum at the concentration of 249 mL of water to 1.0 mL of plant extract

(Rahuman et al., 2009).

Nicotiana tabacum is a valuable commercial crop in the production of tobacco products, however, in Ghana it is usual to find the crop at backyards supposedly to drive away dangerous reptiles. To reduce the cost of preparing botanical insecticides from N. tabacum, the use of poor quality leaves and crop residue may be beneficial. The plant can be easily cultivated by any farmer who desires to exploit its insecticidal potential.

Extraction of the constituents can conveniently be done with water or other common organic solvents (Rahuman et al., 2009). Besides, diversifying the use of the plant beyond the traditional tobacco production may be a sure way of curbing the rapid increase in tobacco consumption in low and middle income countries (Pampel, 2008).

2.11.6 Cassia sophera (Fabales: Fabaceae) sophera senna

Cassia sophera is distributed throughout the tropics. The plant is abundant and grows along roads and uncultivated lands (Kestenholz et al., 2007).

Cassia sophera is reported to have medicinal properties and it has record of use in Bangladesh and India for the treatment of ailments such as asthma, acute bronchitis, cough, diabetes, convulsion of children (Rahaman et al.,

2008). It has been used by peasant farmers in the Northern Ghana to protect their grains in storage (Belmain & Stevenson, 2001). In a laboratory and field experiments, Kestenholz et al. (2007) used dried powered leaves (1 and

5%), hot water and cold water extracts of C. sophera as storage protectants against Sitophilus oryzae of rice and Callosobruchus maculatus of cowpea.

According to that study, differences were observed in the response of the test insects to the treatments at the laboratory and the field even though all the treatments could offer some level of protection. Hot water extract of C. sophera however, was the best based on the overall assessment (Kestenholz et al., 2007). It appears there is little information on the use of C. sophera as a botanical insecticide. Even the few available have been used against storage pests of grains.

2.11.7 Ricinus communis (Malpighiales: Euphorbiaceae) castor oil plant

Ricinus communis is a cultivated shrub of tropical countries and oil from its seeds has been utilised as purgative over the years in many parts of the world (Upasani et al., 2003; Elimam et al., 2009). In Ghana, it usually grows at refuse dumps where there is high supply of organic matter. The seeds of

R. communis are reported to be very poisonous to mammals due to the

47 presence of toxic proteins that exhibit cytotoxic and hemagglutinating characteristics (Upasani et al., 2003). Ricinus communis is reported to be high in flavonoids; the secondary metabolite responsible for its insecticidal properties (Elimam et al., 2009).

In a laboratory bioassay, R. communis at the concentrations of 0.01, 0.02,

0.04 and 0.08 exhibited both antifeedant and toxicity against the tobacco caterpillar, S. litura and castor semilooper, A. janata L. (Rathi &

Gopalakrishnan, 2006). Kodjo et al. (2011) used aqueous leaf, root and seed extracts of R. communis at 20% concentration for leaf and root extracts and

10% concentration for seed oil to control DBM. According to the study, 100

% mortality of 3rd instar larvae was observed in the seed oil. Ricinus communis is also reported to have larvicidal, oviposition deterrence, adult emergence inhibition against two species of mosquitoes, Anopheles arabiensis and C. quinquefasciatus (Elimam et al., 2009). According to

Elimam et al. (2009) larval mortality was observed after 24 hours and the

nd rd LC50 values calculated were 403.65, 445.66 and 498.88ppm against 2 , 3 and 4th instar larvae of A. arabiensis and 1091.44, 1364.58 and 1445.44ppm against 2nd, 3rd and 4th larval instars of C. quinquefasciatus. Fifty percent adult emergence inhibition was 374.97 and 1180.32ppm against 3rd instar larvae of A. arabiensis and C. quinquefasciatus (Elimam et al., 2009).

Upasani et al. (2003) reported that flavonoids in the aqueous leave extract of

R. communis had excellent insecticidal, ovicidal and oviposition deterrence activities against Callosobruchus chinensis L. (Coleoptera: Bruchidae). In their study, methanol extract of both fresh and dried leaves of R. communis

48 resulted in 100% mortality of C. chinensis after nine hours exposure whilst aqueous extract of dried leaves showed slightly lower mortality with petroleum ether performing poorest (Upasani et al., 2003). Ricinus communis has high insecticidal activity and against wide range of pests

(Devanand & Rani, 2008). Moreover, it is abundant in Ghana and farmers can have access to the plant without much difficulty (table 1). Moreover, extraction of the flavonoids can conveniently be done with water (Elimam et al., 2009).

2.11.8 Jatropha curcas (Malpighiales: Euphorbiaceae) physic nut

Jatropha curcas is a drought tolerant, multipurpose plant that is native to the

Americas (Adebowale & Adedire, 2006) The plant grows well in Africa,

Southeast Asia and many other parts of the world (Adebowale & Adedire,

2006; Achten et al., 2007; Acda, 2009). It is usually used as hedge plant in several countries including Ghana, but has recently received attention as a potential source of biodiesel (Acda, 2009).

The genus Jatropha has been found to possess numerous secondary metabolites such as alkaloids, diterpenes, triterpenes, lignans, cyclic peptines (Can-Aké, et al., 2004). Others have reported the presence of saponins, lectin, phytates, protease inhibitors, and curcalonic acid and phorbol esters (Acda, 2009). According to Acda (2009) Jatropha seeds are toxic to mammals, and oil from the seeds has over the years been utilised as insecticide, molluscide, and rodenticide.

Jide-Ojo & Ojo (2011) observed a significant oviposition deterrence of S. zeamais when leaf powder of J. curcas was applied to infested maize. At

5% w/v of the plant material, 26.62 oviposition deterrence was observed but with increasing success rate of application resulting in 76.46 inhibition at

100% w/v. The study also recorded significant insect mortality that was dose dependent.

Jatropha gossypifolia was used to manage Spodoptera exigua Hübner

(Lepidoptera: Noctuidae). In that study, 95% ethanol extract of the leaves was diluted with distilled water (Bullangpoti & Pluempanupat, 2009).

Second instar larvae of the test insect were dipped in the solution for 5 seconds. The study found the LC50 of J. gossypifolia at 35, 000ppm and concluded that its toxicity seems higher than other botanicals such as

Capsicum frutescens and Ocimum sanctum (Bullangpoti & Pluempanupat,

2009). Acda (2009) reported on the insecticidal activity of J. curcas oil in managing a wide range of insect pests including hornworm, Manduca sexta

(Lepidoptera: Sphingidae), Helicoverpa armigera (Lepidoptera: Noctuidae),

Aphis gossypii (Hemiptera: Aphididae), Pectinophora gossypiella,

(Lepidoptera: Gelechiidae) leafhoppers, Empoasca biguttula, Chinese bean weevil, Callosobruschus chinensis, maize weevil, S. zeamais, potato tuberworm moth, Phthorimaea operculella, pink stalk borer, Sesamia calamistis, American cockroach, Periplaneta americana, German cockroach, Blatella germanica and the milkweed bug, Oncopeltus fasciatus.

Jatropha curcas has also shown potential in the control of termites. In a laboratory study, Acda (2009) reported an anti-feeding effect, reduced tunnelling activity and high rate of mortality against the Philippine milk termite Coptotermes vastator (Isoptera: Rhinotermitidae).

Jatropha curcas oil is reported to have been used successfully to manage pests on crops such as cotton, okra and cabbage (Gübitz et al., 1999).

According to Gübitz et al. (1999) Jatropha oil has also been used to control maize and sorghum stem borers; Sesamia calamistis (Lepidoptera:

Pyralidae) and Busseola fusca (Lepidoptera: Noctuidae). Besides the efficacy of this botanical against insects, no negative impact was observed on beneficial insects upon its application. Boateng & Kusi (2008) used

Jatropha oil to manage a population of C. maculatus in stored cowpea at the rate of 1.0 ml to 150g cowpea. According to that study, effectiveness of

Jatropha oil against C. maculatus was dose dependent as 1.0 ml performed better than 0.5 ml per 150g of cowpea.

Even though J. curcas has recently received attention as source of biodiesel, its utilisation for that purpose is yet to be realised in Ghana. Exploiting the plant’s activity against insects will be appropriate. It has high insecticidal activity against several insect pests. It is abundant in Ghana and can be cultivated easily. Moreover, extraction of the plant’s constituents can be done appropriately with water (Gübitz et al., 1999).

Table 2.1 Some available insecticidal plants in Ghana

Family Scientific Common Insecticidal property Economic Availability in name name significance in Ghana Ghana 1 Alliaceae Allium garlic Toxic, and repel Lepidoptera, Spice and Abundant but sativum L. Diptera, Hemiptera pests e.g. DBM, medicinal could be costly cabbage looper, Aphids

2 Annonaceae Annona sour sop, Antifeedant, growth inhibitory and Fruit crop Abundant but muricata and toxic against Lepidoptera e.g. The A. squamosa sweet sop cabbage looper, (Trichoplusia ni)

3 Anacardiaceae Mangifera mango Leave extract toxic to Lepidoptera Fruit crop Abundant (Both indica insect pests e.g. tobacco cut worm local & exotic) (Spodoptera litura), castor semilooper, (Achaea janata

4 Asteraceae Ageratum goat weed Leaf extract toxic to Diptera, Weed Highly abundant conyzoides Coleopterans e.g., Sitophilus zeamais Asteraceae Chromolina Siam weed Toxic to Diptera, Coleopterans e.g. Weed. Highly abundant odorata Sitophilus zeamais Simulium species,

Asteraceae Synedrella Cinderella Leaf and flowers control Lepidoptera Weed, Abundant nodiflora weed e.g. Spodoptera litura medicinal

5 Combretaceae Terminalia tropical Leave extract toxic to Lepidoptera Ornamental Abundant catappa almond tobacco cut worm (Spodoptera plant litura), castor semilooper, (Achaea janata) 6 Compositae Aspilia haemorrhane Controls nematodes but could be Weed. Abundant africana plant exploited for insect control

7 Cucurbitaceae Luffa Egyptian luffa Leaf extract toxic to Lepidoptera e.g. Vegetable, Abundant aegyptiaca and Tobacco cut worm (Spodoptera sponges, weed and Lufa litura), castor semilooper, (Achaea acutangula angled luffa janata)

8 Euphorbiaceae Jatropha physic nut Leaf extract toxic to Lepidoptera Usually as Highly abundant curcas insect pests e.g. tobacco cut worm ornamental (Spodoptera litura), castor plant. Recently semilooper, (Achaea janata) being considered for bio-diesel

Euphorbiaceae Ricinus castor oil plant Leaf extract toxic to Lepidoptera e.g. Ornamental, Abundant communis Tobacco cut worm (Spodoptera Generally weed litura), castor semilooper, (Achaea janata) DBM

9 Fabaceae Cassia sophera senna Controls Coleoptera such as Weed Abundant sophera Sitophilus zeamais, Prostephanus truncates. Fabaceae Tephrosia fish poison, Controls Lepidoptera e.g. For improving spp wild indigo Helicoverpa armigera, soil fertility Available but Maruca vitrata. not abundant

10 Lamiaceae Ocimum basil/ African Leaf extract have toxic show gratissimum basil repellency against Coleopterans, and other O. Hemiptera e.g. maize weevil, Aphids. Medicinal, Highly abundant species spice

11 Meliaceae Azadirachta neem tree Controls wide range of insect pests. Medicinal Abundant indica Lepidoptera, Coleopteran, Hemiptera etc. 12 Piperaceae Piper black pepper, Toxic. as contact insecticide against Spice plant, Abundant guinesis and wide range of insect pests e.g. medicinal P. nigrum Ashanti pepper (Coleoptera) Colorado potato beetle Abundant in Ghana

13 Polygalaceae Securidaca violet tree Molluscicide, insecticide, particularly Medicinal Scarce longeped- Coleoptera stored product pests unculata

14 Rutaceae Citrus spp citrus Extract from peels controls Fruit crop Highly abundant Coleopterans.

15 Solanaceae Capsicum chilli pepper Control pests Wide range of pests Spice and Abundant and frutescens Lepidoptera, Diptera, Hemiptera e.g. medicinal easily cultivated DBM, Aphids, cabbage looper etc. by every farmer

Solanaceae Lycopersicon tomato Leaf extract- repellant and toxic to Vegetable Abundant esculentum Lepidoptera, Hemiptera such as aphids, Corn earworm and

Diamondback moths.

Solanaceae Nicotiana tobacco Toxic to wide range of insect pests. Commercial Abundant tabacum Such as Brevicoryne brassicae, DBM, Colorado potato beetle. tobacco production

16 Verbenaceae Lantana wild sage Control Coleopterans especially Weed Abundant camara storage insect pests e.g. Callosobruchus maculatus Verbenaceae Lippia bush tea Known to control Coleoptera Weed/ Abundant multiflora medicinal Verbenaceae Tectona teak plant Leaf extract toxic to Lepidoptera e.g. Woodlot plant. Highly abundant grandis tobacco cut worm (Spodoptera litura), castor semilooper, (Achaea janata)

2.12 Conclusion

The use of botanicals in pest management is an old practice in many parts of the world. The importance and intensity of use of botanicals in current pest management systems falls below that of the pre-synthetic insecticides era.

There are indications, however, that they may be used more intensively in the years ahead. The qualities such as selectivity, specificity and tolerance to non-target organisms that botanicals possess have attracted attention to the use of plant compound in integrated pest management. Multiple insecticide resistance and eradication of important natural enemies brought on with the use of synthetic insecticides, it is only appropriate that much effort is put into finding alternative pest management strategies of which botanicals provide a promising option.

Several plant species still remain unexploited for their insecticidal purposes; an indication that more potent botanical insecticides could be discovered and added to the already known ones such as the pyrethrum, rotenone, neem ryania, nicotine and sabadilla. Interestingly, several plant species are in the same families as some of these potent and commercially exploited botanicals. Farmers can have immediate access to these plant species whenever they are needed. Most of these plant species can effectively be used in their crude form with simple extraction procedures.

Clearly, botanicals will receive endorsement for wider use by farmers especially those in the developing countries if they are found to be reliable alternatives to the synthetic insecticides. For instance, studies have shown that farmers in Ghana will generally respond positively to the use of safer

pest management options such as botanical insecticides if they available and reliable. Belmain & Stevenson (2001) observed that farmers’ were enthusiastic in using botanicals as an alternative to synthetic insecticides in grain and legume storage. Coulibaly et al. (2007) reported that cabbage growers in Ghana expressed their willingness to use organic pesticides such as botanical insecticides to control P. xylostella and other field pests if they are available, reliable and extension services provide regular technical assistance.

Farmers from developing countries and indeed the world at large stand to benefit immensely if botanical insecticides are widely used in current pest management systems. Whilst farmers aim at maximizing output and minimizing cost of production in order to enhance benefit and subsequently improve on their livelihoods, botanicals offer low-cost pest management option to the resource-limited farmer in the developing world. Apparently, many underprivileged farmers may be unable to purchase commercially extracted botanicals. The possibility of making crude extracts from locally available plant materials provides them with the opportunity of timely pest management. To a larger extent, the world stands to benefit immensely if botanicals are widely used in the pest management systems. The frequently reported pesticidal poisoning of farmers and insecticidal contamination of water bodies and food commodities would be reduced if botanicals are fully incorporated into pest management systems.

Exploiting the insecticidal activity of plants will put some otherwise harmful plants into good. For instance, the Siam weed Chromolaena

57 odorata is a robust and aggressive weed that is reported to threaten the balance of biodiversity in the forest zones (Castel, 2012) in certain parts of the world. Exploiting the potential of this plant will help check its spread.

With premature smoking-related deaths reaching 5 million and estimated to reach 10 million by 2020, tobacco use has become source of worry to the

World Health Organisation and member states (Pampel, 2008). Any important venture that will decrease the availability of tobacco for smoking may cause a reduction in tobacco-related health problems globally.

Expanding the use of N. tabacum in pest management will cause an increase in demand for tobacco which will result in high cigarette prices. This will possibly cause a downward shift in demand for cigarettes, especially in low income countries where access to quality health care may be limited.

Even though botanical insecticides have limitations such as slow acting and inconsistent availability of insecticidal plant materials, they offer promising pest management option to farmers around the globe. Effort must be made towards minimising the limitations of botanicals whilst strengthening their potential in integrated pest management system.

Chapter three

Tri-trophic insecticidal effects of African plants against cabbage pests

3.1 Introduction

Cabbage, Brassica oleracea var. capitata L. (Cruciferae) is an important temperate vegetable crop that grows well in other climatic regions throughout the world (Mochiah et al, 2011a). Despite the importance of cabbage, there are a number of biotic constraints, including insect pests, which hamper its production and consumption (Waiganjo et al., 2011).

Diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera:

Plutellidae) is of European origin and one of the most destructive pest of crucifers worldwide (Mitchell et al., 1997; Obeng-Ofori & Ankrah, 2002).

Yield loss attributed to DBM can be as high as 100% (Weinberger &

Srinivasan, 2009; Waiganjo et al., 2011). Global cost of control and yield loss attributed to DBM has recently been estimated between US$ 4 and 5 billion per annum (Zalucki et al., 2012; Wei et al., 2013). In Ghana, DBM is considered the most important pest of cabbage (Grzywacz et al., 2010).

The cabbage aphid, Brevicoryne brassicae (L.) (Hemiptera: Aphididae) is also an important insect pest of cabbage in Ghana and globally (Mochiah et al., 2011a). The four nymphal stages and the adult aphid are phloem feeders

(Hughes, 1963). Their feeding results in weak, wrinkled leaves that are cupped both outward and inward, resulting in a deformed plant with lower yields (Hughes, 1963; Mochiah et al., 2011a). Indirect damage from their feeding result from the excreta (honeydew) that supports the growth of sooty mould (Hughes, 1963). In addition, the cabbage aphid is a vector of

23 virus diseases of Cruciferae (Flint, 1991). 59

Though both of these pests are attacked by a range of natural enemy species, biological control is rarely considered adequate; to the extent that in Ghana, other parts of Africa, and globally, vegetable growers frequently apply synthetic insecticides to manage DBM, cabbage aphid and other prevalent insect pests of cabbage Gerken et al., 2001; Macharia et al., 2005; Ntow et al., 2006; Devanand & Rani, 2008; Obopile et al., 2008). Synthetic insecticides work relatively quickly, are easy to apply and are not labour intensive (Weinberger & Srinivasan, 2009). There has, however, been an increase in the resistance of DBM and other insect pests of cabbage to insecticides, making their management difficult (Obeng-Ofori & Ankrah,

2002; de Cássia Seffrin et al., 2010). Synthetic insecticides have also been associated with health hazards to humans and animals, environmental pollution, pest resistance, and are unavailable to many peasant farmers such as those in the Ghanaian hinterlands (Devanand & Rani, 2008; de Cássia

Seffrin et al., 2010). Synthetic insecticides are often mishandled and misapplied especially by inexperienced farmers (Ntow et al., 2006;

Coulibaly et al., 2007). In order to avoid the negative impacts of these synthetic insecticides, alternative approaches to managing pests of cabbage and other vegetables must be sought (Ntow et al., 2006; Coulibaly et al.,

2007). Generally, the use of botanical insecticides is more sustainable and has a lower environmental impact than synthetic insecticides (Isman, 2000;

Buss & Park-Brown, 2002; Rathi & Gopalakrishnan, 2006; Devanand &

Rani, 2008; Ogendo et al., 2008). However, current commercially extracted botanical insecticides such as pyrethrum and azadirachtin tend to be relatively expensive and difficult for most smallholder farmers to obtain. To constitute a viable technology for most of the world’s poor farmers,

60 botanical insecticides must be based on plant materials that are cheap and readily available and be simply prepared rather than requiring organic solvents and complex apparatus. Further, extracts need to be benign to natural enemies in order to avoid secondary and resurgent pests, as well as having low phytotoxicity and protecting yields.

Though simple plant extracts are commonly promoted for use in home gardens, there is growing interest in their potential for farmers in developing countries. In Ghana, for example, chili Capsicum frutescens (Solanaceae) extract concentrations of 15, 20 and 30g/L of water gave a significant reduction in B. brassicae numbers compared to λ-cyhalothrin (Fening et al.,

2011). Other work, in Uganda, demonstrated that crude aqueous extracts of tobacco, Nicotiana tabacum (Solanaceae) and Tephrosia sp. (Fabaceae) were as efficacious as the synthetic insecticides, Cypermethrin® and

Fenitrothion® in reducing emergence of bruchid beetle, Callosobruchus sp.

(Kawuki et al., 2005) Similarly, in Nigeria, extracts of garlic, Allium sativum (Asparagales: Amaryllidaceae) chili pepper, ginger, Zingiber officinale (Zingiberales: Zingiberaceae) neem, Azadirachta indica

(Sapindales: Meliaceae) tobacco and sweetsop, Annona squamosa

(Magnoliales: Annonaceae) have been successfully used to control pests of cowpea (Ahmed et al., 2009). In Ghana, crude leaf and seed extracts of neem tree have been used extensively in managing pests of crops such as cabbage, lettuce and cowpea (Obeng-Ofori & Ankrah, 2002; Mochiah et al.,

2011b).

Pest management using local materials offers farmers the opportunity to reduce production costs, as the plants often grow wild in and around farms

61 so can be obtained with little effort and zero or minimal cost. In addition, cultivation of insecticidal plant species that might otherwise be locally scarce represents scope for agricultural diversification and complementary income sources. Some plant species with potentially useful insecticidal properties in the families of Meliaceae, Rutaceae, Asteraceae, Piperaceae,

Compositae, Lamiaceae, Euphorbiaceae, Combretaceae and Annonaceae are common weed, shrub and tree species on and around farms (Devanand &

Rani, 2008).

Given the need for alternatives to conventional insecticides and the potential utility of extracts from locally-growing plants, the aim of the current study was to identify from amongst plants that are common in Ghana those with utility against cabbage pests. A field cage experiment was conducted to screen crude water plus detergent extracts of nine such plants against P. xylostella and B. brassicae. Five of these plants were then trialed in two field experiments conducted in the major and minor rainy seasons. Pest incidence usually varies between the two rainy seasons, higher in minor than the major rainy season. It was therefore important to test the treatments in both seasons in order to make a full assessment of their performance against the pests.

3.2 Materials and methods

3.2.1 Study site

Experiments were conducted at the Council for Scientific and Industrial

Research (CSIR)-Crops Research Institute (CRI), Kwadaso, Kumasi, Ghana

(Latitude 6°43'N Longitude 1°36'W; 287m elevation). The cage experiment

62 was carried out between January and April whilst the field experiments were between May and August and July and October, 2012 for major and minor rainy seasons, respectively. The study site was part of the wet semi- deciduous forest ecological zone of Ghana with annual rainfall between

1200 and 1600mm. Mean minimum and maximum ambient temperature during both experiments ranged between 22-31ºC, with the mean relative humidity ranging from 75-78% and 78-82% for the cage and field experiments, respectively.

3.2.2 Experimental design and treatment preparation

3.2.3 Field cage experiments

Plutella xylostella and B. brassicae were collected from local cabbage fields and cultured in cages containing potted cabbages. Permission to collect the initial P. xylostella and B. brassicae for the laboratory culture was granted by the local farmer. Multiple cages were used for each species so that any affected by disease or parasitism could be quarantined from further use. The two herbivores were tested against each treatment in separate experiments.

For each experiment, treatments consisted of four controls and nine botanical treatments and were set up in a randomised complete block design with three replications. Positive control treatments were the two synthetic insecticides, Attack® (emamectin benzoate) and Lambda Super® 2.5 EC

(lambda-cyhalothrin), whilst negative control treatments were 0.1%

Sunlight® detergent solution and tap water. Attack® and Lambda super® were applied at the recommended rates of 1.5mL/L and 4.8mL/L of water, respectively. The nine botanical treatments were prepared from each of the following plant species; goat weed, Ageratum conyzoides, Siam weed,

Chromolaena odorata, Cinderella weed, Synedrella nodiflora, hot pepper,

Capsicum frutescens, tobacco, Nicotiana tabacum Cassia, Cassia sophera, physic nut, Jatropha curcas, castor oil plant, Ricinus communis and basil,

Ocimum gratissimum. For most plant species fresh leaves were collected from within 1km of the experimental site and 30g fresh weight of each was pounded into a pulp in a wooden mortar using a wooden pestle. Reflecting the fact that plant chemistry can vary between individuals, the plant materials for this study were collected from several individual plants from more than five different locations and were thoroughly mixed before the required quantities were taken as a sub-sample to prepare the extracts. The plant identifications were confirmed by a botanist prior to the preparation of the extracts. Voucher specimens of all the plant species were deposited at the herbarium of the National Genebank, of CSIR- Plant Genetic Resource

Research Institute, Bunso, Eastern region, Ghana for future study. The mortar and pestle were washed with a sponge and detergent and given multiple rinses of tap water after each plant material. For C. frutescens, ripe fruits were obtained from a local market and homogenised using an electric blender. Processed plant materials were each mixed with 1L tap water containing 0.1% Sunlight® detergent solution to give a 3% w/v final concentration then sieved through fine linen into a 2L capacity hand sprayer for immediate application.

For each experiment, a 38-day-old potted cabbage plant (cv. Oxylus) with six true leaves was covered with an insect-proof net fitted with an elastic band at the base and a zipper at the side to enable access. Potted plants were covered with the net immediately after potting. Seedlings for potting were raised on a seed bed that was completely covered with insect proof net from day of sowing

64 till seedlings were potted. Plants were arranged 60cm apart on a one metre high wooden platform. For the P. xylostella experiment, plants were infested with 10 second generation (from field collection); third instar larvae using a fine brush.

Larvae were allowed to feed for three days by which time they had reached fourth instar larval stage before the application of treatments. For the B. brassicae experiment, 20 third generation adult cabbage aphids were transferred onto the plants using a fine camel hair brush and were allowed to establish colonies for seven days before treatment. All treatments were applied to the point of runoff to infested potted plants through a zipper at the side of the cage. Only one treatment application was done in P. xylostella experiment whilst two treatment applications were done in the B. brassicae experiment with a seven day interval between the two applications.

Figure 3.1 Cages for rearing Plutella xylostella and Brevicoryne brassicae to obtain cohorts for cage experiment.

Figure 3.2 Nursery of cabbage seedling in inset-proof netting for experiments

Figure 3.3 Field cage experiments set up

Figure 3.4 Treatment applications through a side zipper in field cage experiments

3.2.4 Data collection

Numbers of P. xylostella larvae were assessed 48 hours after spraying and percentage mortality calculated. Brevicoryne brassicae were much more numerous and difficult to count without disruption so were scored using a modified method of Afun et al. (1991) as: 0 = absent, 1 = a few scattered individuals, 2 = a few isolated small colonies, 3 = several small isolated colonies, 4 = large isolated colonies, 5 = large continuous colonies.

3.2.5 Open field experiments Land was cleared of weeds after which beds were raised. Cabbage (cv. Oxylus) was grown from certified seed sown on a raised bed in the field. The young seedlings were protected from pest attack with mosquito-proof netting.

Standard cultural and agronomic practices such as weed control, watering and earthing-up of soil to improve aeration were employed during the growing

67 period. The experimental design of the field trials consisted of a randomised complete block design with seven treatments and four replications. Well decomposed poultry manure at the rate of 500g per plant was incorporated into the soil two weeks before seedlings were transplanted. Cabbage seedlings were transplanted at the four true leaf stage (30 days after sowing). Spacing was 0.5 x 0.5m and plots measured 1.5m x 2.5m, resulting in 24 plants per plot. A 2m- wide unplanted alley was left between each plot to avoid spray drift between adjacent plots. Treatments were extracts of A. conyzoides, C. odorata, S. nodiflora, N. tabacum, R. communis, Attack® and tap water control. Plant extract preparation was as for the field cage experiments. A separate 15L capacity knapsack sprayer was used to apply each for the treatments solutions to the point of runoff including to the underside of the leaves. Applications commenced 14 and 21 days after transplanting of seedlings for minor and major rainy seasons, respectively and were re-applied weekly thereafter. There were seven and six weekly applications for minor and major rainy seasons respectively.

3.2.6 Data collection

Insect presence was assessed weekly on eight plants from the two innermost rows of each plot. Infestation by B. brassicae was scored as described for the field cage experiment but P. rapae and the common natural enemy taxa, ladybird beetles (Coccinellidae) (adults and larvae) and hoverflies (Syrphidae)

(larvae) were counted in situ. Samples of larvae of coccinellids and syrphids were cultured in the laboratory to the adult life stage to allow identification by comparison with labelled specimens in the insect museum of the Entomology

Section, CRI. At harvest, all the plants (24) in each plot were used for yield and insect damage assessment.

Figure 3.5 A section of the major rainy season field experiments showing 2m wide alley on the left

3.2.7 Statistical analysis

Field cage experiments

Percentage P. xylostella mortality data were corrected using Abbott’s formula

(Abbott, 1925). To normalise data, percentage and score values were arcsine square root and log(x+1) transformed, respectively, before analysis. The normality of the data was tested with the Shapiro-Wilk test. Back transformed means were presented in the results. Data from the cage experiments were analysed using PROC (Univariate) the general linear model procedure of

Statistical Analysis System (SAS) (SAS, 2008). When significant (P<0.05) differences were obtained, means were separated using the Student Newman-

Keuls (SNK) test.

Open field experiments

Mean weekly count data for P. xylostella and natural enemies and the score data for B. brassicae were computed. Brevicoryne brassicae score data were analysed using repeated measures analysis in residual maximum likelihood

(REML) using treatment and week as fixed effects and plot.time as random effect. The treatment effect was partitioned into (i) water control versus experimental treatments (the botanical extracts and Attack® pooled) and (ii) experimental treatments. Examination of the weekly pest and natural enemy numbers showed many zeros so these data were analysed using generalised linear mixed model (GLMM) with a Poisson distribution and fixed and random terms as specified above for B. brassicae data. Mean cabbage head weight was analysed using ANOVA and SNK test. The proportion of cabbage heads in each plot with Lepidoptera damage were analysed using generalised linear model with a binomial distribution and logit link. All analyses were carried out in Genstat V15.

3.3 Results

3.3.1 First trophic level: plant yield and damage

In the major rainy season open field experiment S. nodiflora, C. odorata and N. tabacum as well as Attack® had significantly (df 6; F=18.08; p<0.01) higher head weights than the water control whilst the last two mentioned botanical treatments were superior to the conventional insecticide (Table 3.

1). For proportional damage level, all botanical treatments and Attack® performed significantly (df=6,21; χ2=5.87, p=0.001) better than water though A. conyzoides and C. odorata were not as effective as the conventional insecticide.

In the minor rainy season experiment, botanical treatments and the Attack® did not differ significantly in terms of head weight and all performed significantly (df=6; F=4.46; p<0.006) better than the water control. In the major season, when head weights were higher, the proportion of heads damaged did not differ significantly (df=6,21; χ2=2.56, p=0.051) between treatments (Table 3. 3).

Figure 3.6 Cabbage heads from plots sprayed with an extract of Ageratum conyzoides

Figure 3.7 Cabbage heads from plots sprayed with Attack®

3.3.2 Second trophic level: herbivore dynamicsField cage experiments All of the botanicals were as effective as Attack® in reducing numbers of P. xylostella while detergent solution and tap water were less effective (Table

3. 2). All the botanical treatments and Attack® significantly reduced the B. brassicae score more than Lambda super®, 0.1% Sunlight® detergent solution and tap water in the cage experiment.

Open field experiments

The five botanical treatments and Attack® had significantly lower overall numbers of P. xylostella compared to the water control during the major season (df=1,154; F=50.67; p<0.001) (Figure 3.9). The five botanicals and

Attack® differed significantly (df=5,154; F=3.27; p=0.008) with C. odorata giving levels of P. xylostella suppression greater than Attack® whilst the

72 other botanicals treatments were comparable in efficacy to Attack®. Results for P. xylostella were similar in the minor season (Figure 3.10). The five botanical treatments and Attack® had significantly lower overall numbers of

P. xylostella compared to the water control (df=1,179; F=21.49; p<0.001).

The five botanicals and Attack® differed significantly (df=5,179; F=2.51; p=0.032) with C. odorata and S. nodiflora giving levels of P. xylostella suppression greater than Attack® whilst the other botanicals treatments were comparable in efficacy to Attack®.

Brevicoryne brassicae infestation scores in the major season were significantly lower in the five botanical treatments and Attack® compared to the water control (df=1,28; F=67.99; p<0.001) (Figure 3.11). Infestation levels in the water control were particularly high in the early-midseason and this is reflected in a statistically significant control.week interaction

(df=1,80.7; F=16.84; p<0.001). In the minor season, B. brassicae infestation was significantly lower in the five botanical treatments and Attack® compared to the water control (df=1,30.1; F=10.25; p<0.001) (Figure 3.12).

Infestation levels in the water control were highest in the mid-late season and this was reflected in a statistically significant control.week interaction

(df=1, 94.5; F=5.78; p<0.018).

Figure 3.8 Cabbage plant from control (sprayed with tap water) plots showing severe Plutella xylostella damage in minor rainy season field experiment.

3.3.3 Third trophic level: natural enemy dynamics

Numbers of ladybird beetles, predominantly Coccinella magnifica

(Coleoptera: Coccinellidae), in the major season were significantly less numerous in the five botanical treatments and Attack® than in the water control (df=1,154; F=15.5; p<0.001). The five botanicals and Attack® differed significantly (df=5,154; F=6.39; p=0.001) with all botanicals having significantly higher coccinellid numbers than the Attack® treatment and significant separation of the botanical treatments with A. conyzoides having the highest predator counts (Table 3).

Numbers of hoverflies, predominantly Episyrphus balteatus (Diptera:

Syrphidae), in the major season did not differ significantly between the five botanical treatments and Attack® compared to the water control (df=1,154;

F=0.41; p=0.521). The five botanicals and Attack® did differ significantly

(df=5,154; F=5.11; p<0.001) with all botanicals having significantly higher hoverfly numbers than the Attack® treatment. Of the botanical treatments, A. conyzoides, S. nodiflora and R. communis had significantly higher numbers of this predator taxon than did C. odorata and N. tabacum (Table 3).

Numbers of spiders (Araneae) in the major season did not differ significantly between the five botanical treatments and Attack® compared to the water control (df=1,151; F=1.63; p=0.204. The five botanicals and

Attack® did differ significantly (df=5,151; F=3.16; p=0.01) with all botanicals having significantly higher spider numbers than the Attack® treatment though C. odorata had lower numbers of this predator taxon than did S. nodiflora, the botanical treatment in which spiders were most numerous (Table 3).

Numbers of all three natural enemy taxa were lower in the minor season than in the major season and did not exhibit significant treatment differences.

3.4 Discussion

The effectiveness of the botanical treatments in this study was generally equivalent to that of conventional, synthetic insecticide Attack® in managing

P. xylostella and B. brassicae. Poor control of B. brassicae was observed for

Lambda Super® in the field cage experiment. A similar observation was made for Bossmate® (lambda-cyhalothrin) which failed to control B. brassicae in a field experiment in Ghana resulting in a reduced yield of plots sprayed with Bossmate® compared to plots sprayed with garlic, chili pepper and Attack® (Fening et al., 2011). The lack of control by this conventional insecticide was attributed to resistance in the aphid population and this is

75 likely to have also been the case in the present study. The efficacy of the botanical treatments against B. brassicae and P. xylostella supports the findings of other previous studies of these and related pests. For example, extracts of Azadirachta and Melia azedarach have been successfully used to control B. brassicae (Rando et al., 2011; Kibrom et al., 2012). Similarly, leaf extracts of R. communis and S. nodiflora as well as J. curcas, have been used to manage the lepidopterans Spodoptera litura and Achaea janata

(Kestenholz et al., , 2007; Devanand & Rani, 2008; Ogendo et al., 2008).

Another treatment used in the present study, N. tabacum has previously been reported to have been used to manage both P. xylostella and B. brassicae (Kianmatee & Ranamukhaarachchi, 2007).

In the current study, P. xylostella and B. brassicae populations were effectively suppressed with the evaluated botanicals and Attack®. Insect pests of brassicas such as the P. xylostella have been managed successfully with botanical insecticides (Leatemia & Isman, 2004; Charleston et al.,

2005; Charleston et al., 2006).

Conversely, P. xylostella has been difficult to control with synthetic insecticides in many regions of the world because of the development of insecticide resistance (Leatemia & Isman, 2004; Sarfraz et al., 2005;

Charleston et al., 2006; Kianmatee & Ranamukhaarachchi, 2007). Plutella xylostella is reported to be the first crop pest to have developed resistance against dichlorodiphenyltrichloroethane (DDT) and the first to develop resistance to Bacillus thuringiensis (Bt) insecticides (Baker & Kovaliski,

1999; Leatemia & Isman, 2004; Reuben et al., 2006) thus, any botanical that is able to offer a significant control will be considered valuable. In Brazil,

76 de Oliveira et al., (2011) reported that it is normal for farmers to apply between 15-20 insecticide sprays within a cropping season with at least three applications in a week, without success, in an effort to reduce yield losses caused by P. xylostella. The ability of the botanicals to significantly manage the populations of P. xylostella, as well as B. brassicae, in this study is an indication of their potential usefulness in integrated pest management (IPM) of cabbage, especially for resource-limited farmers.

The numbers of P. xylostella and B. brassicae were generally higher in the minor rainy season compared with the major rain season. This may be due to the fact that the amount of rainfall and the frequency is usually high in the major rainy season and this could disrupt the reproduction of the insects or dislodge them from plants.

There are suggestions that natural enemies should be the first consideration in any pest management intervention (Koul & Dhaliwal, 2003). Any integrated approach to pest management must thus, be compatible with natural enemy conservation. Emamectin benzoate (Attack®) is regarded as a novel semi-synthetic derivative of the natural product abamectin in the avermectin family and is known to be effective against a wide range of pests

(Jansson et al., 1997). However, in this study, Attack® caused a significant reduction in the numbers of ladybirds, hoverflies and spiders. Both of the pests monitored in the present study are attacked by a wide range of natural enemies when free from the effects of insecticide use (Furlong et al., 2013).

Until the early 1960s when large scale application of synthetic insecticides was introduced to commercial vegetable farming, P. xylostella was not a

77 major pest in China (Liu, Wang, Guo, He, & Shi, 2000). The use of pesticides that are harmful to the third trophic level need to be minimised in favour of less harmful plant protection compounds to allow biological control to play a role in integrated pest management (Ayalew & Ogol,

2006). In particular, an active natural enemy fauna can reduce the frequency with which insecticides applications are required and kill survivors of insecticide application to prevent the development of resistance in the pest population. Not all botanical insecticides are able to play this role. Some such as pyrethrum are broad spectrum in nature (Buss & Park-Brown, 2002;

Dubey et al., 2011). Those used in the present study appeared much less toxic to the natural enemies that were common in the study site, ladybirds, hoverflies and spiders, than was the conventional insecticide, Attack®.

These members of the third trophic level had densities on the botanical extract treated plants similar to the water control though C. odorata gave consistently over all three natural enemy taxa lower than the best performing botanicals. Given the relatively small scale of the experiments, with plots separated by just 2m, the Attack® plots would have been subject to potential recolonisation by natural enemies moving from neighbouring plots. That numbers of predators were consistently low in the Attack® treatment despite this phenomenon highlights the negative impact of such broad spectrum insecticides on biological control. The consistently low numbers of natural enemies in plots sprayed with Attack® could also result from the possibility that this pesticide repelled them rather than being due to mortality.

Notwithstanding the higher numbers of natural enemies in the water control, this treatment was heavily attacked by both B. brassicae and P. xylostella

78 and had poor first trophic level performance. These metrics show that effective biological control by natural enemies was not achieved in this system solely by withholding insecticide and that botanical insecticides have an important role in pest suppression.

The compatibility of the botanical treatments in this field study with common natural enemies is in broad agreement with earlier work on some other botanical insecticides. No negative impact was found on the parasitoids, Cotesia plutellae and Diadromus collaris when M. azedarach and A. indica extracts were applied against P. xylostella (Charleston et al.,

2006). Reports by (Fening et al., 2011) and (Mochiah et al., Banful, et al.,

2011a) indicate that effective control of cabbage pests with garlic and chili pepper at 10, 20 and 30g/L of water was achieved whilst beneficial insects were preserved. However, (Fening et al., 2011) cautioned that, at higher concentrations, botanicals could possibly have some detrimental effect on natural enemy populations because their numbers reduced with increasing concentration of garlic and chili pepper extracts.

Effects at the second and third tropic levels are complemented in the present study by marked effects at the first trophic level, an important observation in the use of simply prepared readily available botanical insecticides.

This study has revealed that extracts of C. sophera, O. gratissimum, N. tabacum, S. nodiflora, R. communis, A. conyzoides, J. curcas and C. odorata have good potential for use in managing pests of cabbage. Two factors make this observation particularly important for poor farmers in this region and potentially in other parts of the world. First, the plant extracts were prepared by simple mechanical means using only detergent and water.

This contrasts with the often employed-organic solvent, steam distillation and other approaches used for preparing botanical insecticides. Thus, the types of treatments shown to be promising in the present study could be easily prepared by resource-limited farmers or as cottage industry enterprises in rural villages. Second, the plants themselves are cheap and readily available to farmers. Many grow as weeds so are immediately available at no cost, whilst chili and tobacco are widely grown so offering scope for the use of crop residues, damaged or excess materials in plant protection.

Cabbage is often eaten raw and managing its pests with botanical insecticides will contribute markedly to food safety. The beneficial effects of the botanical extracts at the first, second and third trophic levels provide justification for further studies of such plant protection products including the range of pests to which they are active and the measurement of sublethal effects on various natural enemy taxa. The labour intensive nature of the preparation of sprays based on these plant extracts is not likely to be a constraint on their use by smallholder families but likely to be an impediment to usage on large scale commercial farms. This obstacle may be overcome, however, if efforts are made to commercially extract the active components and package them for sale.

Table 3.1Effect of plant extracts and synthetic insecticides on mean (±SE) yield and heads with borer holes per plot in field experiments during the major rainy season, 2012 at Kumasi, Ghana.

Treatment Major season head Minor season Minor season weight (kg) head weight (kg) damaged heads (proportion)1

A. conyzoides 0.44a 0.35b 0.156b

C. odorata 0.70c 0.36b 0.135b

S. nodiflora 0.53b 0.36b 0.115ab

N. tabacum 0.67c 0.40b 0.125ab

R. communis 0.41a 0.37b 0.125ab

Attack® 0.56b 0.38b 0.083a

Tap water 0.35a 0.23a 0.219c

P <0.001 0.006 0.001

Means within a column with different letters differ significantly (P < 0.05)

1 Major season proportional damage did not differ significantly between treatments (df=6,21; χ2=2.56, p=0.051).

Table 3.2 Effect of plant extracts and synthetic insecticides on mean (±SE) percentage reduction of Plutella xylostella numbers and Brevicoryne brassicae infestation score (0 = absent to 5 = large continuous colonies) in field cage experiments at Kumasi, Ghana.

Treatment P. xylostella B. brassicae

A. conyzoides 1 00 ± 0.00 a 0.17 ± 0.17b C. odorata 100 ± 0.00 a 0.17 ± 0.17b

S. nodiflora 93 ± 0.06a 0.00 ± 0.00 b C. frutescens 93 ± 0.06 a 0.33 ± 0.33b

N. tabacum 93 ± 0.06 a 0.00 ± 0.00 b C. sophera 66 ± 0.17ab 0.00 ± 0.00b J. curcas 66 ± 0.08ab 0.00 ± 0.00 b R. communis 85 ± 0.07 a 0.00 ± 0.00 b O. gratissimum 89 ± 0.05a 0.17 ± 0.017b Lambda super® 51 ± 0.11 b 2.33 ± 0.37 a Attack® 1 00 ± 0.00a 0.00 ± 0.00 b 0.1% Sunlight® solution 21 ± 0.11 c 2.33 ± 0.60a

Tap water 6 ± 0.06 c 3.00 ± 0.50 a

Means within the same column with different letters are significantly (P < 0.05) different from each other

Table 3.3 Effect of plant extracts and synthetic insecticides on mean (±SE) yield and heads with borer holes per plot in field experiments during the minor rainy season, 2012 at Kumasi, Ghana.

Treatment Mean head Mean yield Mean no. weight (kg) (kg/plot) heads with borer holes

A. conyzoides 0.35 ± 0.01a 8.4 ± 0.67a 3.75 ± 0.25ab

C. odorata 0.36 ± 0.02a 8.6 ± 0.72a 3.25 ± 0.25bc

S. nodiflora 0.35 ± 0.23a 8.4 ± 0.93a 2.75 ± 0.48bc

N. tabacum 0.39 ± 0.02a 9.4 ± 0.62a 3.00 ± 0.41bc

R. communis 0.37 ±0.01a 8.9 ± 0.30a 3.00 ± 0.41bc

Attack® 0.38 ± 0.01a 9.1 ± 2.31a 2.00 ± 0.41c

Tap water 0.23 ± 0.01b 5.5 ± 0.57b 5.25 ± 0.48a

P ˂ F 0.05 0.0067 0.0067 0.0005

Means within the same column with different letters are significantly (P < 0.05) different from each other.

4.5 A. conyzoides Attack® C. odorata N. tabacum R. communis S. nodiflora Tap water 4

3.5

2.5 per plantper

2 larvae 1.5

1 P. xylostella P.

0.5 Mean

0 WK 1 WK 2 WK 3 WK 4 WK 5 WK 6 -0.5 Week Figure 3.9 Effects of plant extracts and synthetic insecticide on mean (±SE) P. xylostella count in a field experiments during the major rainy season, 2012 at Kumasi, Ghana.

A. conyzoides Attack® C. odorata N. tabacum R. communis S. nodiflora Tap water

larvae per pantper larvae 4

P. xylostellaP. 2

Mean 1

0 WK 1 WK 2 WK 3 WK 4 WK 5 WK 6 WK 7 Week

Figure 3.10 Effects of plant extracts and synthetic insecticide on mean (±SE) P. xylostella count in a field experiments during the minor rainy season, 2012 at Kumasi, Ghana.

A. conyzoides Attack® C. odorata N. tabacum R. communis S. nodiflora Tap water 4

3.5

2.5 score

1.5 B. brassicaeB.

1 Mean 0.5

0 WK 1 WK 2 WK 3 WK 4 WK 5 WK 6 -0.5 Week Figure 3.11: Effects of plant extracts and synthetic insecticide on mean (±SE) B. brassicae score in a field experiments during the major rainy season, 2012 at Kumasi, Ghana.

A. conyzoides Attack® C. odorata N. tabacum R. communis S. nodiflora Tap water 4

3.5

2.5

score 2

1.5

B. brassicaeB. 1

0.5 Mean 0 WK 1 WK 2 WK 3 WK 4 WK 5 WK 6 WK 7

Week

Figure 3.12 Effects of plant extracts and synthetic insecticide on mean (±SE) score of B. brassicae score in a field experiments during the minor rainy season, 2012 at Kumasi, Ghana.

A. conyzoides Attack® C. odorata N. tabacum R. communis S. nodiflora Tap water 6

2 Coccinellidae number per plantper number Coccinellidae 1 Mean 0 WK 1 WK 2 WK 3 WK 4 WK 5 WK 6

Week

Figure 3.13 Effects of plant extracts and synthetic insecticide on mean (±SE) count of Coccinellidae in a field experiments during the major rainy season, 2012 at Kumasi, Ghana.

A. conyzoides Attack® C. odorata N. tabacum R. communis S. nodiflora Tap water 4

3.5

2.5

1.5

1 Coccinellidae number per plantper number Coccinellidae 0.5

Mean 0 WK 1 WK 2 WK 3 WK 4 WK 5 WK 6 WK 7

Week

Figure 3.14 Effects of plant extracts and synthetic insecticide on mean (±SE) weekly count of Coccinellidae in a field experiments during the minor rainy season, 2012 at Kumasi, Ghana

A. conyzoides Attack® C. odorata N. tabacum R. communis S. nodiflora Tap water 6

Syrphidae per plant per Syrphidae 2

Mean 1

0 WK 1 WK 2 WK 3 WK 4 WK 5 WK 6

Week

Figure 3.15 Effects of plant extracts and synthetic insecticide on mean (±SE) Syrphidae count in a field experiments during the major rainy season, 2012 at Kumasi, Ghana.

A. conyzoides Attack® C. odorata N. tabacum R. communis S. nodiflor Tap water 4

3.5

2.5

1.5

Syrphidae number per plantper number Syrphidae 0.5

0 Mean WK 1 WK 2 WK 3 WK 4 WK 5 WK 6 WK 7 -0.5 Week

Figure 3.16 Effects of plant extracts and synthetic insecticide on mean (±SE) Syrphidae count in a field experiments during the minor rainy season, 2012 at Kumasi, Ghana.

Chapter four

Cost: benefit analysis of botanical insecticide use in cabbage: implications for smallholder farmers in developing countries

4.1 Introduction

To reduce the negative impacts of synthetic insecticides, safer alternative approaches to managing pests of vegetables must be considered by growers, especially those who do not have the expertise and equipment for safe handling and use of synthetic insecticides (Ntow et al., 2006; Coulibaly et al., 2007). Approximately three million agricultural workers experience pesticide poisoning each year globally, and about 20,000 deaths are directly linked to agrochemical use (Dinham, 2003; Darko and Akoto, 2008). Less than 1% of pesticides applied on crops reach the target pest, the rest can contaminate soil, water, air and food (Koul et al., 2004). In developing countries such as Ghana food commodities often contain pesticide residues, often above the maximum residue limit (Darko and Akoto, 2008; Armah,

2011). In Ghana pesticides have been found in water, sediments, food commodities and even breast milk in areas where intensive vegetable production occurs due to injudicious use of synthetic insecticides (Ntow et al., 2006; Essumang et al., 2008; Bempah et al., 2011).

In many developing countries, farmers are illiterate or speak and read indigenous dialects, whilst pesticides labels are printed in foreign languages

(Isman, 2008). For example, even though Ghana’s official language is

English, it is not uncommon to find pesticides on the market that are labelled in French or Chinese (Asante and Ntow, 2009), a practice which

exacerbates the inability of farmers to understand pesticides labels. This leads to unacceptable practices in handling and use of pesticides by some farmers such as tongue-testing of diluted insecticides to determine their potency (Ntow et al., 2006; Timbilla and Nyarko, 2006; Williamson et al.,

2008; Asante and Ntow, 2009).

Nearly 75% of all deaths associated with pesticidal poisoning occur in developing countries even though they use only 15% of global pesticide supply (Koul et al., 2004; Darko and Akoto, 2008; Armah, 2011). The use of banned insecticides, applying insecticides in excess of the recommended rates due to insects resistance, using insecticides meant for industrial crops such as cocoa and cotton for vegetables, using empty pesticides containers for storing drinking water are practiced in Ghana and often lead to pesticidal poisoning (Ntow et al., 2006; Williamson et al., 2008).

Botanical insecticides based on specific compounds or crude extracts from plants with activity against insects offer a safer alternative for managing pests such as the diamondback moth (DBM), Plutella xylostella L.

(Lepidoptera: Plutellidae), a key pest of crucifers which has developed resistance to most of the available synthetic insecticides (Kianmatee and

Ranamukhaarachchi, 2007; Isman, 2008; Ogendo et al., 2008). Botanicals are also usually safer for non-target organisms, making them preferable to the synthetic insecticides (Charleston et al., 2006).

In a survey, Gerken et al. (2001) showed that between 14% and 25% of farmers in Ghana, used traditional products for crop protection. Plants such as Azadirachta indica (Sapindales: Meliaceae), Cassia sophera (Fabales:

Fabaceae), Cymbopogon schoenanthus (Poales: Poaceae), Ocimum americanum (Lamiales: Lamiaceae), Securidaca longepedunculata

(Polygalales: Polygalaceae), Synedrella nodiflora (Asterales: Asteraceae),

Chromolaena odorata (Asterales: Asteraceae), Capsicum frutescens

(Solanales: Solanaceae), Allium sativum (Asparagales: Amaryllidaceae) and

Carica papaya (Brassicales: Caricaceae) have been used in Ghana (Owusu,

2000; Belmain et al, 2001; Obeng-Ofori and Ankrah, 2002; Fening et al.,

2011). A study in Uganda revealed that crude aqueous extracts of locally available plants such as tobacco and Tephrosia sp. were as efficacious as

Cypermethrin® and Fenitrothion® (synthetic insecticides) in reducing damage caused by bruchid beetle, Callosobruchus sp. in cowpea (Kawuki et al, 2005). In Nigeria, extracts of garlic, chilli pepper, ginger Zingiber officinale (Zingiberales: Zingiberaceae), neem, Azadirachta indica

(Sapindales: Meliaceae), tobacco, Nicotiana tabacum (Solanales:

Solanaceae) and sweetsop, Annona squamosa (Magnoliales: Annonaceae) have been used to manage field pests of cowpea (Ahmed et al., 2009).

Farmers who adopt botanicals as a means of plant protection may enhance the activity of natural enemies. For example extracts of Melia azedarach and Azadirachta indica (Sapindales: Meliaceae) were sprayed on the parasitoids, Cotesia plutellae (Hymenoptera: Braconidae) and Diadromus collaris (Hymenoptera: Ichneumonidae) in a laboratory bioassay and found not to cause harm (Charleston et al., 2006). Similarly, application of Annona

94 squamosa (Magnoliales: Annonaceae) and Aglaia odorata (Sapindales:

Meliaceae) controlled DBM whilst having no negative impact on natural enemies (Dadang & Prijono, 2009). Ayalew & Ogol (2006) advised that the use of harmful pesticides be discontinued in favour of less harmful ones such as neem-based products to achieve the potential of natural enemies in managing DBM and other pests of crucifers. Reflecting this, DBM was not a major pest of brassicas in China until the early 1960s when large scale application of synthetic insecticides was introduced to commercial vegetable farming (Liu et al., 2000).

Despite the foregoing potential advantages of botanical insecticides, they have not gained widespread usage globally. The causes of this are complex.

Farmers usually want a very rapid knock-down to demonstrate effective application to the crop and toxicity to the target yet many botanical insecticides operate more slowly and some by modes of action other than toxicity (repellence for example) (Isman, 2006). Second, the availability of many potentially effective botanicals plant materials is constrained in many countries by the need to meet expensive regulatory requirements that mean only products that can service a large market are registered. Further, the costs, availability and consistency of plant materials may be a limiting factor. One aspect of this is inconsistent activity of different provenances in the same plant species which can mean that farmers often use plant materials that do not always work (Stevenson et al., 2012). The approach of smallholder farmers preparing their own inexpensive botanical insecticides from locally-available plant materials that they develop a knowledge of and confidence in offers a solution to these problems. The use of botanicals must, however, be economically viable if their potential is to be realised.

The plant materials from which botanical insecticides are made are often available locally and are usually obtained without cost (Belmain et al.,

2001) making them cheaper compared to their synthetic counterparts.

Though the efficacy of various botanical insecticides has been explored in many studies that report pest numbers and, often, effects on natural enemies, there are few reports of the yields from crops treated with botanical insecticides and a dearth of information on the cost: benefit ratios for botanical insecticides compared with conventional insecticide use. This study quantified the costs and benefits of using crude extracts of readily available insecticidal plant materials, an untreated control and a synthetic insecticide in controlling insect pests of cabbage in Ghana.

4.2 Materials and methods 4.2.1 Costs

The costs of plant protection were recorded in two field experiments conducted during the major and minor rainy seasons of 2012 at the Crops

Research Institute, Kumasi, Ghana. Plant protection treatments of crude extracts of readily available insecticidal plants (botanicals) were compared with the synthetic insecticide, emamectin benzoate (Attack®) and an unsprayed control. Botanicals involved in the study were the goat weed

(Ageratum conyzoides) (Asterales: Asteraceae), Siam weed (Chromolaena odorata) (Asterales: Asteraceae), Cinderella weed (Synedrella nodiflora)

(Asterales: Asteraceae), tobacco (Nicotiana tabacum) (Solanales:

Solanaceae), and castor oil plant (Ricinus communis) (Malpighiales:

Euphorbiaceae). Most plant materials were collected from weedy, uncultivated areas in the immediate vicinity of the test site and without purchase cost therefore the associated costs were only labour for the 96 collection, preparation and application plus the value of the soap for extraction. However, since tobacco has commercial value and leaves that could have been sold were used in preparing the extract, the amount that would have been realised from the sale of the leaves was added as a cost in addition to other costs as described above for other botanicals. For plant protection using Attack®, the cost of the insecticide was added to the labour cost of spraying. Throughout the study, labour cost was based on the existing wage for an unskilled labour at the locality at the time of the study which was equivalent to US$ 8.33 per man day. Treatments were prepared as detailed in Amoabeng et al. (2013) and compared in field experiments with four replicates and plot size of 1.5m x 2.5m at spacing of 0.5m x 0.5m resulting in 24 plants per plot. For the purposes of the economic analyses, values were calculated on a per hectare basis. In the major season, a total of l2 days of labour were used for collecting and preparing the botanicals afresh for each of the botanical treatments. There were six sprayings in the major rainy season whilst the minor season experiment received seven sprayings. This frequency of spraying was used to give comparability with local practice in the use of synthetic insecticides. A total of 18 days of labour was costed for spraying each of the treatments. Sunlight® liquid soap for extraction of each botanical was purchased for US$ 2.00. Attack® was costed at US$ 99.11/ha for six applications.

In the minor season, 14 man days were used for the collection and preparation of each botanical whilst 20 man days were used for spraying.

Sunlight® liquid soap was purchased for US$ 2.00 whilst US$ 19.44 was used to purchase tobacco leaves. Cost of Attack® was US$ 122.33 and 20 man days were required for spraying. The externalities such as potential

97 impacts on the environment, natural enemies, and farm worker and consumer safety associated with each of the treatments were not considered in the analyses.

At harvest, plot yields were weighed and recorded. Mean head weight was calculated for each plot by dividing the plot weight by number of plants per plot. Cabbage heads from each plot were sorted into undamaged or with caterpillar feeding damage, individually weighed and sold at the prevailing price on the local market. The number of damaged and undamaged heads were converted to percentage damaged and undamaged heads per plot. The

Ghanaian currency, Cedi (¢) was converted to US$ at the prevailing exchange rate of US$ 1: ¢1.8 during the study period. Undamaged heads fetched US$ 0.56 and US$ 0.83 per kg for the major and minor seasons respectively whilst damaged heads fetched one-third of these prices.

Revenue was converted to a per hectare basis by extrapolating the plant population of plots based on a plant spacing of 0.5m x 0.5m taking into account unplanted alleys to facilitate movement within the field. This resulted in a total plant population of 35,000 per hectare.

4.2.2 Economic analysis Mean head weight per plant, percentage of damaged heads and undamaged head yield per hectare were subjected to analysis of variance of statistical analysis system (SAS) (SAS, 2005). Percentage data were arcsine square root transformed prior to the statistical analysis. On achieving significant differences (P<0.05) mean separation was performed using Student

Newman-Keuls test. The number of undamaged heads per treatment was multiplied by average head weight per plant to obtain yield per hectare for each treatment. Total income was obtained by adding incomes from 98 undamaged heads and that of damaged heads. Income from undamaged yield was obtained by multiplying the head yield per hectare by the selling price per kg of cabbage head. Income from damaged heads was obtained by multiplying damaged head yield by selling price per kg of damaged heads.

No premium was achieved for the botanical-sprayed produce. Net benefit per hectare for each treatment was derived by subtracting the total cost of plant protection from total income (Shabozoi et al., 2011). Benefit over unsprayed control for each sprayed treatment was obtained by subtracting the income of the control treatment from that of each sprayed treatment. The cost: benefit ratio of each treatment was derived by subtracting the income of the control treatment from the net income of each sprayed treatment and the products were divided by total cost of plant protection for each treatment

(Shabozoi et al., 2011).

4.3 Results

Table 4.1 Cost and benefit analysis of managing pests of cabbage with botanical insecticides and synthetic insecticide (Attack®) in field experiments during the major rainy season of 2012 in Kumasi, Ghana.

Treatment Mean head Percent Marketable yield Cost of Income Income Total Net benefit Benefit over Cost: weight per damaged heads (t/ha) plant from from income (US$/ha) unsprayed Benefit plant (kg) protection marketable damaged (US$/ha) treatment ratio (US$/ha) yield heads (US$/ha) (US$/ha) (US$/ha) Goat weed 0.44 ± 0.08bc 11.1 ± 3.26abc 13.69 ± 2.70bc 231.89 7,244.16 324.79 7,586.95 7,355.08 1,446.90 1: 6.23

Siam weed 0.70 ± 0.05a 9.7 ± 1.37bc 22.12 ± 1.75a 231.89 12,389.16 451.00 12,840.16 12,608.27 6,700.09 1: 28.89

Cinderella weed 0.53 ± 0.06ab 11.1 ± 3.26abc 16.49 ± 2.10b 231.89 9,234.93 391.20 9,626.13 9,394.24 3,486.06 1: 15.03

Tobacco 0.67 ± 0.03a 11.1 ± 1.41abc 20.89 ± 1.05a 248.56 11,805.67 494.56 12,300.23 12,051.67 6,143.49 1: 24.71

Castor oil plant 0.42 ± 0.05bc 19.5 ± 1.38ab 11.83 ± 1.75bc 231.89 6,626.76 544.64 7,171.40 6,939.51 1,031.33 1: 4.45

Attack® 0.56 ± 0.03ab 8.0 ± 0.00c 18.03 ± 1.10b 238.00 10,097.92 297.92 10,395.84 10,157.84 4,249.66 1: 17.86

Control 0.35 ± 0.03c 21.0 ± 2.39a 9.91 ± 1.21c 0.00 5,419.40 488.78 5,908.18 5,908.18 0 -

Means within columns with letters were statistically analysed and those with different letters differ significantly (P < 0.05). *Means calculated from the same raw data used in Amoabeng et al. 2013

Table 4.2 Cost and benefit analysis of managing pests of cabbage with botanical insecticides and synthetic insecticide (Attack®) in field experiments in

Treatment Mean head Percent Marketable yield Cost of Income Income Total Net benefit Benefit over Cost: weight per damaged heads (t/ha) plant from from income unsprayed Benefit plant (kg) protection undamage damaged (US$/ha) treatment ratio d heads heads (US$/ha) (US$/ha) (US$/ha) (US$/ha) (US$/ha)

Goat weed 0.35 ± 0.01a 16.0 ± 1.07ab 10.33 ± 0.35a 287.01 8,540.70 584.80 9,089.50 8,802.48 3,090.60 1: 10.76

Siam weed 0.36 ± 0.02a 13.5 ± 1.04bc 10.90 ± 0.70a 287.01 9,046.17 476.28 9,522.45 9,235.44 3,523.56 1: 12.28

Cinderella weed 0.35 ± 0.03a 11.5 ± 2.01bc 10.89 ± 1.05 a 287.01 8,998.24 394.45 9,392.69 9,105.68 3,393.80 1: 11.82

Tobacco 0.39 ± 0.02a 12.5 ± 1.71bc 11.99 ± 0.70a 306.44 9,913.31 477.75 10,391.06 10,088.62 4,372.74 1: 14.28

Castor oil plant 0.37 ± 0.01a 12.5 ± 1.7bc 11.38 ± 0.35a 287.01 9,404.94 453.25 9,858.19 9,571.18 3,859.30 1: 13.45

Attack® 0.38 ± 0.01a 8.5 ± 2.10c 12.23 ± 0.35a 289.00 10,100.69 316.54 10,417.23 10,128.23 4,416.35 1: 15.28

Control 0.23 ±0.01b 21.9 ± 2.45a 6.32 ± 0.35b 0.00 5,218.25 493.63 5,711.88 5711.88 0 -

Means within columns with letters were statistically analysed and those with different letters differ significantly (P < 0.05).*Means calculated from the same raw data used in Amoabeng et al. 2013

101

4.3.1 Yield and income All botanical treatments and the synthetic insecticide in both seasons were superior financially compared to the control treatment in which cabbages were heavily attacked by DBM and cabbage aphid, Brevicoryne brassicae

(L.) (Hemiptera: Aphididae). Accordingly, treatments other than the control had higher undamaged head yields which resulted in revenue that exceeded the cost of the plant protection regime (Tables 4.1 and 4.2). The cost of plant protection using Attack® was higher than all of the botanicals for the two seasons except tobacco. There were differences in the total cost of plant protection between the major and the minor rainy season because there was one spray more in the minor season than in the major rainy season. In the major rainy season, plots sprayed with an extract of Siam weed or tobacco recorded the highest undamaged cabbage head yield of 22.12 and 20.89 t/ha respectively; significantly higher than other treatments including Attack® at

18.03 t/ha (Table 4.1). Yields of plots sprayed with goat weed and castor oil plant extracts were 13.69 and 11.83 t/ha respectively which were not significantly higher than the control which yielded 9.91 t/ha. In the minor rainy season, Attack® gave an undamaged yield of 12.23 t/ha and was followed by tobacco at 11.99 t/ha. However, there were no significant differences in undamaged yield per hectare between the treatments though all had significantly higher undamaged yields than the control which produced just 6.32 t/ha (Table 4.2).

Undamaged head yields were higher in the major rainy season than the minor season but total income for the minor rainy season was comparatively higher due to the higher market price. Whilst a yield of 11.83t/ha in the major rainy season gave a total income of US$ 7,171 a slightly lower yield

of 11.38 t/ha had total income of US$ 9,858 in the minor rainy season. Even though income from damaged heads contributed to the total income for all treatments, the amounts were small and not markedly different among the treatments. The highest benefit over the control treatment of US$ 6,700 was obtained from plots sprayed with an extract of Siam weed in the major rainy season whilst the lowest was US$ 1,031 obtained from plots sprayed with an extract of castor oil plant. The Attack® treatment had an intermediate benefit over control treatment of US$ 4,249. The difference between the highest and the lowest benefit over control treatment was US$ 5,669. In the minor rainy season, the highest benefit over the control treatment of US$ 4,416 was obtained from plots sprayed with Attack®. Plots sprayed with an extract of tobacco had benefit over control of US$ 4,372. There were only slight differences in the benefit over the control treatment obtained from the treatments. Difference between the highest and the lowest benefit over the control in the minor rainy season was US$ 1,326.

4.3.2 Cost: benefit In the major rainy season, the best cost: benefit ratio of 1: 29 was for Siam weed treatment in the major rainy season. It was followed by the tobacco treatment with a cost: benefit ratio of 1: 25. Plots sprayed with Attack® had a cost: benefit ratio of 1: 18. The lowest cost: benefit ratio of 1: 4 was obtained for plots sprayed with an extract of castor oil plant. In the minor rainy season, the highest cost: benefit ratio of 1: 15 was observed for plots sprayed with Attack® which was followed closely by plots sprayed with an extract of tobacco with 1: 14. The lowest cost: benefit ratio in the minor rainy season was 1: 11 and observed on plots sprayed with an extract of goat weed. 103

4.4 Discussion In the major season, Siam weed and tobacco gave higher total income than

Attack®. These two treatments produced significantly higher undamaged head yield than the rest of the treatments and resulted in higher incomes. In the minor rainy season only slight differences in income was observed among the treatments. This was because there were no significant differences between sprayed treatments in undamaged yields to result in higher differences in income. In this study tobacco was more costly to use than Attack®. This is because tobacco is a commercially valuable crop and marketable leaves were used in preparing the extracts, thus, attracting cost.

The labour cost of preparation in addition to the cost of purchase of tobacco leaves accounted for higher cost in using tobacco in this study. However, tobacco was more financially beneficial to use than Attack® in the major rainy seasons. This was because plots sprayed with extract of tobacco produced significantly higher yields with corresponding higher total income enough to offset the higher cost associated with its use. If extracts of tobacco based on crop residues and malformed leaves were shown to be efficacious, the cost associated with their use could be reduced so giving a still more attractive cost: benefit ratio.

4.4.1 Labour cost

Even though farmers may obtain insecticidal plant materials without material cost, the labour associated with collection and preparation is usually significant which makes the total cost of plant protection with botanicals close to that of purchasing and using the synthetic insecticide option. In a study to develop simple botanicals for farmers in Ambon 104

(Indonesia), Leatemia (2003) reported that less economic benefit may be derived from the use of botanicals due to the labour cost involved in collection and preparation. Labour cost at the location where botanicals are used will be an important factor of the overall benefit that would be derived from their use. In several parts of the developing world, many resource- limited farmers do not have the financial capacity to purchase synthetic insecticides or commercially formulated botanicals but have free and adequate labour to prepare and use botanicals irrespective of the labour requirements. Thus, they will still find the use of locally prepared botanicals more convenient.

4.4.2 Cost: benefit ratio

Cost: benefit ratio is an indicator of the relative economic performance of the treatments (Aziz et al., 2012). A ratio of more than one indicates the economic viability of the treatment compared with the control treatment. In this study, cost: benefit ratios of between 1: 29 and 1: 4 indicates that treatments were biologically effective and resulted in significant return on investment in plant protection. Siam weed and tobacco were more economically viable than Attack® in the major rainy season but Attack® was marginally superior to the most active botanicals in the minor rainy season.

Siam weed and tobacco consistently gave better cost: benefit ratio than other botanicals. However, since all the botanicals gave cost: benefit ratios more than one, farmers have the option of selecting from an array of botanicals to make beneficial spray extracts.

The cost: benefit ratios calculated in this study are similar to those obtained by Patel et al. (1997) but higher than that obtained by Shabozoi et al. (2011).

105

These three studies calculated the ratios in the same manner (economic analyses only on cost of plant protection). Whilst Shabozoi et al. (2011) obtained a cost: benefit ratio of 1: 4.13 from application of a neem-based botanical, Patel, et al. (1997) obtained a ratio of 1: 14.18 and 1: 12.59 for botanical (neem extract) and synthetic insecticide (endosulfan) respectively in managing insect pests of pigeon pea. Arivudainambi et al. (2010) reported a much less favourable ratio of 1: 1.29 which was lower than that in this study. This could be because this study and others analysed only the cost of plant protection and calculated the cost: benefit ratio based on the income of the control treatment. Arivudainambi et al. (2010) who used extracts of Cleistanthus collinus, Cleome viscose Gynandropsis pentaphylla,

Andrographis paniculata and commercial neem extract in comparison with the synthetic insecticide endosulfan in managing pests of amaranth, on the other hand, analysed both cost of cultivation and plant protection and did not make reference to the income obtained from the control treatment in calculating the cost: benefit ratios. However, economic analysis in this study was useful because, besides the spray type applied; all other input costs were constant for all treatments.

The cost: benefit ratio, the total income and the benefit obtained from each treatment is greatly influenced by the price of the commodity. The results of this study show that whilst some of the treatments had higher yield in the major season than the minor season, total income and cost: benefit ratios were lower in the major season compared to the minor season. This was because price for cabbage heads was 50% higher in the minor rainy season harvest than the major season one. It must be stated that cost of plant protection was even higher in the minor season than in the major season as a

106 result of the additional spray application whilst total income for the controls in the two seasons did not differ markedly.

In the current study, cabbage heads from plots sprayed with synthetic insecticide and those from botanical plots were sold for the same price. If cabbage heads from plots protected with botanicals were sold for premium price there would be corresponding increases in economic benefit. In developed countries where human health is of paramount importance, there are premium prices for food commodities that do not have pesticide contamination and health-conscious consumers eagerly patronise (Njoroge and Manu, 1999). In Ghana, however, food commodities including vegetables such as cabbage on the market are not currently identified as organic and inorganic. Reasons for this include the relative lack of sophistication in the market (simple marketing chains lacking quality control measures) and a lack of any organic certification scheme or residue monitoring program for food commodities. As a result of the absence of such regulatory factors, it is difficult to establish a pattern of price premiums for organic produce because it would be difficult to gain customer trust, easily corrupted and impossible to police. Increasing awareness of health hazards of insecticide-contaminated food commodities is gradually changing consumers’ perception of food commodities even in the developing countries. For instance, vegetable consumers in Ghana and

Benin expressed their desire to pay more than 50% premium prices for vegetables that will be certified as free from pesticide contamination

(Coulibaly et al., 2007). Organic food producers in developing countries should raise awareness of the benefits of pesticide-free food commodities to obtain the deserved prices for their commodities and subsequently obtain

107 higher benefits. In addition, organic food producers may also have access to the US and the EU markets where strict compliance to pesticide levels in food commodities is a requirement (Njoroge and Manu, 1999).

Some plant compounds, including some tested in this study, may be toxic to humans but this bald fact needs to be tempered by some more specific aspects of detail. First, the extracts used in this study (and the form of use we advocate as a result of our findings) were crude, 3%, water-based extracts rather than being the concentrated form of the specific compounds that some plants are known to synthesise and that can be toxic to mammals at high concentrations. It is known that the harmful effects associated with plant compounds are largely alleviated through the use of crude plant preparations in which concentrations of the substances usually range from 1

% to 5% (Isman, 2008). Second, the level of risk associated with the use of plant extracts at worst poses no greater risk to human health than does use of conventional insecticides. Finally, we demonstrate efficacy of crude extracts from several plant species in addition to those, such as tobacco, for which toxicity is known to be an issue.

4.5 Conclusion

This study has shown that crude extracts of readily available plants offer cost-effective plant protection alternatives to synthetic insecticides. This was evident in the favourable cost: benefit ratios of the botanical treatments.

Of these, Siam weed and tobacco extracts gave significantly higher undamaged head yields and commensurately more favourable economic benefit and cost: benefit ratio, than Attack®. Smallholder farmers especially those in the developing countries who have free access to such plant 108 materials and have the labour availability stand to gain immensely. The use of synthetic insecticides has been linked with causing hazards to humans, animals and the environment. Botanicals are generally regarded as safer to users, consumers, animals and the environment due to their non-persistent nature (Buss and Park-Brown, 2002). In contrast, synthetic insecticides are often inaccessible to resource-limited farmers or are hazardous to use due to poor access to safety equipment and adequate training in safe use.

Tempering this generality, however, some botanical compounds are as toxic as their synthetic counterparts. For instance, nicotine from Nicotiana sp. has

LD50 (lethal dose) of 50mg/kg in rats and is acutely toxic so extracts of this plant are not completely safe to users and the environment (Isman, 2008;

Rosell et al., 2008) though compounds that are hazardous in pure form are safer to use in a crude extract state (Isman, 2008) where concentrations of the active components are usually below 5%. Rechcigl & Rechcigl, 2000 stated that “if botanicals insecticides are to be widely used, many ecological and environmental problems will be overcome; even the best known products; pyrethrin and rotenone are not persistent, and none of the botanicals has shown to have negative impact on the environment”.

Chapter five

General discussion and conclusion

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5.1 Introduction

The use of botanicals is generally considered as an ideal tactic in an IPM as plant-based insecticides have a minimal effect on non-target organisms

(Buss & Park-Brown, 2002). They, however, play only a limited role in current IPM systems (Isman, 1997, 2008). Issues regarding their practical in

IPM especially on a larger scale continue to be discussed. For instance,

Isman (1997) and Regnault-Roger & Philogène (2008) pointed out that efficacy which is only one of the requirements for registering insecticides has confined many botanicals to the laboratory. This is because they may not offer effective pest control under field conditions. Further, those that have proven efficacious beyond the laboratory such as neem products still have challenges such as inconsistent availability of the plant materials, standardisation of extracts and quality control with respect to active components, and regulatory approvals (Isman, 1997). In the developing countries, another issue of importance, probably is logistic constraints in terms of facilities for commercial extraction of botanicals (Morse et al.,

2002).

Whilst faced with the above challenges that do not encourage the wider use of botanicals, the positive attributes of botanicals are sufficient to merit a sustained interest in exploiting their potential as crop protectants. For instance, the selectivity and specificity of botanicals to the target pest is a major benefit that plant-based insecticides offer. In addition, the biodegradability and non-persistence, low to moderate mammalian toxicity

(Buss & Park-Brown, 2002) and the practicability of combining several compounds that may show an overall synergy are important attributes of

110 botanicals that other crop protectants such as synthetic insecticides may not have. Again, botanicals act at different targets at different developmental stages in an organism and that may delay insect resistance (Regnault-Roger

& Philogène, 2008) should make botanical insecticides the preferred choice for pest management.

In developing countries such as Ghana where there are often reported cases of fatalities due to injudicious use of synthetic insecticides, (reviewed

Chapter 1, section 1.1) botanical insecticides may be useful in the quest to reduce problems associated with misuse of synthetic insecticides. For instance, even though vegetables provide important nutrients needed for normal body functioning in humans, many people in Ghana will avoid fresh vegetables due to the general notion that vegetable commodities on the market are contaminated with synthetic insecticides. The use of botanicals will stimulate consumer confidence and enhance food acceptability especially fresh vegetables in countries such as Ghana.

In an attempt to make botanicals available, accessible and acceptable to smallholder brassica farmers in Ghana, this thesis aimed at evaluating the potential of using readily available insecticidal plants in managing insect pests of cabbage in the Ashanti region of Ghana. Three objectives were set to help in achieving this aim. The first was to conduct caged plant assays to identify the activity of extracts from shortlisted plants out of 24 readily available insecticidal plant species in Ghana that were listed in this thesis

(Table 2.1). The bioassays were done on P. xylostella and B. brassicae; two important pests of cabbage in Ghana. The second objective was to assess the

111 practicability of using the most effective plant materials based on the cage bioassay in field trials against wider range of cabbage pests. Two field experiments were conducted; one each in the major and the minor rainy seasons. The field experiments also sought to provide information on the effect of the botanicals on natural enemies and beneficial arthropods. The third objective was to do a cost: benefit analysis of using botanicals and synthetic insecticides. This objective was important to the overall aim of the thesis because economic considerations are important in pest management intervention as pest management contributes a significant percentage in the overall cost of production.

5.2 Field cage bioassays on P. xylostella and B. brassicae

Bioassay is an important tool used to assess the activity of compounds on insects (Chow et al., 2005). This was the first step in achieving the aim of the study. In this bioassay (Chapter three) whole plants in cages were used to mimic a field situation. Cage plant bioassays were important to the overall aim of the thesis as it was the first practical step in determining the activity of the plants against P. xylostella and B. brassicae (Chapter 3). This was necessary because most of the shortlisted plants had been exploited by other authors in managing insect pests of stored products mostly in the order

Coleoptera (reviewed in Chapter two, sections 2.9.1 to 2.9.8) whist the targeted pests in this thesis were in the orders Lepidoptera and Hemiptera.

This chapter demonstrated that simple extraction procedure with water as solvent could result in efficacious plant extracts. The encouraging results from the two bioassays suggested an opportunity for resource-limited

112 farmers to prepare their own extracts for use whenever needed. Even though for the purpose of consistency Sunlight® liquid soap was used for the extraction throughout this thesis, it is expected that farmers may use their locally available soaps for extraction and get comparable results.

In chapter three, extracts of the tested insecticidal plants had activity against

B. brassicae and P. xylostella and this was in general agreement with other studies. For instance, N. tabacum, R. communis were used to control P. xylostella (Chapter 2, table 1) (Kodjo et al., 2011; Rando et al., 2011).

Jatropha curcas has been used to control other lepidopteran such as S. litura and A. janata but not P. xylostella. Capsicum frutescens was successful against B. brassicae and P. xylostella in a field trial (Fening, 2011)

The efficacy of the botanicals was comparable to Attack® but better than

Lambda super® (lambda-cyhalothrin) in managing P. xylostella. Lambda super® did not reduce B. brassicae numbers. Earlier studies had reported a similar results when Bossmate® (lambda-cyhalothrin) did not reduce the population of B. brassicae in the field (Fening, 2011). The results show that

P. xylostella and B. brassicae might have developed some level of resistance to lambda-cyhalothrin at this area. This may probably be because the chemical has been used to manage pests of brassicas continuously over the years. In Pakistan B. brassicae exhibited very low resistance to lambda- cyhalothrin and emamectin benzoate in 2007 and 2008 but with continuous use, moderate to high level of resistance was observed in 2009 and 2010

(Ahmad & Akhtar, 2013). Whilst P. xylostella is known to have develop resistance to most of the available conventional insecticides, B. brassicae

113 was better managed with lambda-cyhalothrin than Bt in Ethiopia (Ayalew,

2006). This may mean that B. brassicae has not been exposed to lambda- cyhalothrin long enough to develop resistance in the area where Ayalew &

Ogol (2006) conducted the study. To avoid insects’ resistance to insecticides, it is necessary to alter the insect management option or rotate the available insecticides rather than continuously use one chemical for a long period of time.

5.3 Effects of the botanicals on cabbage pests in the field

In chapter three, five out of the nine botanicals tested in the cage experiments were selected and evaluated in field trials. The five were chosen as they were effective in the cage experiments, abundant, readily available and with the exception of except N. tabacum the remaining ones do not have other commercial value. In the Ashanti region of Ghana, there are two rainy seasons within a year; major (April to July) and minor

(September to November). Pest incidence usually varies between the two rainy seasons, higher in minor than the major rainy season. It was therefore important to test the treatments to both seasons in order to make a full assessment of their performance against the pests.

Chapter three showed that botanicals have activity against P. xylostella and

B. brassicae not only in confined experiments but also in field trials. The botanicals also had activity against other pests such as Hellula undalis,

Pieris rapae, Bemisia tabaci, Phyllotreta sp that were observed in the field experiments. The range of insect pests in this study was similar to those reported by other authors who conducted their studies (Timbilla & Nyako,

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2001; Fening, 2011; Mochiah et al., 2011a) at the same area. Snails

(mollusks) were a threat to early field establishment as they could cut several plants within a night. Snails are becoming important pest of cabbage in the Ashanti region of Ghana. Two authors had earlier reported about the damage caused by snails to cabbage in the region (Fening, 2011; Mochiah et al., 2011a). Snails were managed by handpicking and destroying them. It is important to note that even though the numbers of H. undalis were not alarming, a single larva infesting a plant at the pre-heading stage could result in a complete damage to a whole plant as they bore into the growing tip of the plant. At best, there is the formation of multiple heads which are not marketable. The few plants that were attacked by H. undalis did not produce any marketable cabbage head.

Chapter three revealed that some of the botanicals managed the populations of the various pests better than Attack®. For instance in the major rainy season, the botanicals except C. odorata and A. conyzoides were more effective than Attack® against B. brassicae. Again, in the minor rainy season all the botanicals except A. conyzoides were better than Attack® in reducing the population P. xylostella. Effective management of pests with the botanical insecticides is consistent with other studies. Plutella xylostella which is known to be resistant to several synthetic insecticides have been managed with botanicals (Charleston et al., 2006; Kianmatee &

Ranamukhaarachchi, 2007; Fening, 2011; Kodjo et al., 2011). Botanicals on the other hand do not easily induce insect resistance (Scott et al., 2008).

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Chapter three supported that fact that many botanical insecticides do not have knock down effect on the target pests as exhibited by synthetic insecticides (Isman et al., 2011). Evidently, there was no complete eradication of B. brassicae population after any treatment application. The botanicals might have exhibited different modes of action such as repellent, antifeeding, oviposition deterrence, anti-juvenile development in managing populations of the pests.

The leaves of cabbage plants sprayed with botanicals appeared different to those sprayed with Attack® and tap water. Whilst plants sprayed with either

Attack® or tap water had glossy, grayish-green appearance, those sprayed with the botanicals appeared greenish. It can be assumed that the true colour of the leaves of the variety was exhibited by those plots that were sprayed with only tap water. The implication is that the botanicals might have imparted some greenish colouration to the leaves. A similar observation was made (Fening et al., unpublished) when garlic and chilli pepper were used to manage pests of cabbage and with Attack® as positive control. Glossiness of cabbage leaves has been likened with the plant’s ability to withstand pest attack (Stoner, 1990; Ellis et al., 1996). It is not clear whether botanicals work based on colour change in cabbage.

5.4 Effects of the botanicals on natural enemies

In chapter three, four natural enemy taxa (three predators; Coccinellidae,

Syrphidae, Araneae and the parasitoid, Cotesia plutellae) were observed in

116 the field experiments. The numbers of coccinellids and syrphids were high compared to the Araneae and C. plutellae. While the predators were present in all the two seasons, C. plutellae was observed only in the minor rainy season. It is not certain what might have accounted for that observation.

Botanicals in this study could be considered as crop protectants compatible with natural enemy activity. They did not have negative impact on the natural enemies as their numbers were higher on botanical plots than the synthetic insecticide plots. This observation confirms earlier reports that botanicals are generally safe to natural enemies and non-target insets

(Charleston et al., 2006; Isman, 2006; Smitha & Giraddi, 2006). It must be mentioned that some botanical compounds such as the pyrethrum have wide activity range and may not be completely safe to all stages of development of natural enemies (Schmutterer, 1997; Buss & Park-Brown, 2002). Natural enemies alone did not cause significant reduction in pest population in this study. Although plots sprayed with only tap water had higher numbers of natural enemies they also had higher numbers of the pests. The implication may be that local natural enemy density was insufficient to biologically manage the pests. This was evident by the significantly lower marketable head yield recorded on plots sprayed with tap water. In areas where injudicious use of harmful insecticides is prevalent, population densities of natural enemies are usually below the level that can effect significant biological control (Ooi, 1992). The use of less harmful crop protectants such as the botanicals should be practiced to encourage the local buildup of natural enemy populations.

5.5 Effects of botanicals on cabbage yield and quality

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Cabbage head yield for plots sprayed with botanical insecticides as reported in chapter three was similar to plots sprayed with Attack®. Mean cabbage head yield of 0.7kg obtained was lower than that obtained by Fening (2011) or Baidooet al. (2012) (Chapter three) but higher than the 0.55kg obtained by (Mochiah et al. (2011a) at the same study area. In all these studies, the same cabbage variety, Oxylus was used. Factors such soil fertility levels

(Mochiah et al., 2011a), rainfall amounts and distribution (Simpson et al.,

2012), differences in incidence and severity of pest and other climatic factors might have contributed to the differences in head yield between this study and that of others. The availability of nitrogen has been found to significantly influence the yield of brassicas (Veromann et al., 2013).

Interestingly, cabbage heads obtained from botanical plots and Attack® were similar in terms of quality.

5.6 Economic implications of the use of botanicals for the smallholding farmer

Farming, like any other business, is an economic venture and profit maximization is a major goal. Insect pest management is a significant investment and constitutes a relatively greater percentage of the total cost of crop production especially in vegetable crops that often have wider range of pests. Investment on insecticides is estimated to cost between 25 and 65% of the total cost of production of brassicas in Kenya (Grzywacz et al., 2010). In south and Southeast Asia, insect pest management costs about 33 to 50% of the total material cost of vegetable production (Srinivasan, 2012). These percentages may be high because in such areas multiple applications are often made which are usually a prophylactic measures. Poorly executed pest

118 management can cause complete crop failure in vegetable crops such as cabbage. Managing cabbage pests can be capital intensive (reviewed in

Chapter 1, section 1.1) thus, if cost-effective option such as botanicals are applied maximum profit may be obtained.

Chapter four showed that pest management with locally available botanicals is cheaper and economical than synthetic insecticides. This supports

Arivudainambi et al. (2010) who found that botanicals are less expensive than synthetic insecticides. This was evident by the higher cost: benefit ratio of the botanicals compared to the synthetic insecticides (chapter four). In addition to the financial benefit of using locally available plants in managing pests, Isman (2008) mentioned that safeguarding human health is an additional advantage of using botanicals. Buss & Park-Brown (2002), however, found that botanical pest management is more expensive than using synthetic insecticides. This was probably due to the fact that commercially extracted botanical compounds were used in that study.

Factors such as the form of the botanical insecticide (crude or refined) and economic value of the plants from which the extracts are prepared may determine whether it is more expensive than the synthetic ones. In chapter four it was found that an extract of tobacco was more expensive to use the

Attack®. Labour cost involved in preparing the extracts together with the cost of the plant materials may make commercially important plants more expensive to use botanicals. Fening et al. (unpublished results) found similar results when garlic and chilli pepper were used to manage pests of cabbage.

Due to the processes involved in extraction, purification and standardization, the use of commercially extracted botanicals such as

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Neemix® and Garlic Barrier® may also be more expensive than synthetic insecticides. Thus, it may be economically rewarding for smallholder farmers in developing countries of the tropics to use botanicals due to the ready availability of plant materials (Belmain & Stevenson, 2001; Isman,

2008).

This study found a higher cost: benefit ratio in some botanicals plots than others whilst the synthetic insecticide gave intermediate cost: benefit ratio

(Chapter four). There is direct relationship between the efficacy of the crop protectants, yield, total income and cost: benefit ratio. In chapter four, all the botanicals had cost: benefit ratio of more than one indicating that all treatments were profitable. Any of the botanicals can be selected in preparing extracts based on their availability to the farmer.

5.7 Recommendations for future research

Chapter three showed that the readily available insecticidal plants extracted with 0.1 % Sunlight® liquid detergent in cold water and diluted to a 3% concentration were able to effectively manage P. xylostella, B. brassicae and other pests whilst preserving natural enemies. However, there are other aspects of the botanicals that should be addressed. First, attempt should be made to comparatively test the efficacy of extracts prepared by the use of locally made soaps for extraction to make it more convenient for resource- limited farmers. Second, lethal, sublethal and the LC50 concentrations of the various botanicals should be determined for the two key pests; P. xylostella,

B. brassicae. Concentrations below and above the 3% used in the current study should be used for each plant material to identify the optimal

120 concentration of each. Third, laboratory bioassays should be conducted to quantify the effect of the botanicals on natural enemies such as C. plutellae.

Fourth, attempts should be made to compare the insecticidal activity of the various parts of the plants and to isolate and identify the insecticidal compound. Fifth, attempt should be made to commercially extract, standardise and package the active compounds of the plant materials for farmers who do not have the required labour to prepare the crude extracts.

Finally, plant materials used in this study should be combined to determine if there is synergy among them.

5.8 Conclusions

This thesis has shown that locally available insecticidal plants have activity against pests of cabbage. Some of the crude extracts of the botanicals were equally as officious in managing the pests as Attack® (a commercially available synthetic insecticide) both in caged experiments and the two field experiments. Interestingly, all the botanicals were better than Lambda

Super® (lambda-cyhalothrin) in reducing the numbers of B. brevicoryne in the caged experiments. The study showed that plots sprayed with the botanicals had higher numbers of natural enemies. The indication is that the botanicals did not have negative effects on the natural enemies. Yield and quality of cabbage heads produced from plots sprayed with the botanicals and the Attack® were similar in this study. This study has shown that the use of locally available botanicals is cheaper than synthetic insecticides and thus is more cost-effective.

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As human, animal and environmental health concerns around agricultural produce continuous to gain grounds it is expected that developing countries will exploit the potential of botanicals in pest management. Many tropical and sub-tropical developing countries have native or naturalised plant species with activities against economically important insects. Till now, the full potential of many plant species remain unexploited. Efforts should also be made in sustaining the availability of insecticidal plant materials by planting species that may be in short supply with continuous and intensive exploitation.

Whilst it is impossible to use unregistered botanical products in the developed countries due to legal restrictions, regulations in the developing countries are usually more relaxed. For instance, in Ghana, there is no legal framework concerning registration of biopesticides including botanicals, and thus farmers can use botanicals for domestic food production. Isman

(2008) pointed out that, while it may seem irresponsible to advocate for the use of unregistered products due to health concerns, there is enough evidence that with the exception of very few plant-based insecticides, crude plant extracts pose little risk to life compared to their synthetic counterparts.

It is certain from the current low usage of botanicals that they cannot replace synthetic insecticides in crop protection now or in the next few years.

However, botanicals can contribute significantly in IPM programmes especially in the developing countries if more studies are conducted into their activities against insects. The unique characteristics of botanicals such having synergy among the various compounds, ability to delay insecticidal

122 resistance and their mildness to non-target insects make them ideal in IPM programmes.

Even though some botanical compounds may not be benign to all non-target organisms, they are safer in the crude form. This is because concentrations of their active components often do not exceed 5% (Isman, 2008). If botanicals will intensively be incorporated in pest management systems, many ecological and environmental problems will be overcome.

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