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ABSTRACT

Trials were carried out in both screen house and field during 2014 cropping season at Samaru, Zaria to study the Economic Injury Levels (EIL) and to evaluate some cowpea varieties for field resistance to legume pod borer (Maruca vitrata (G.) Fab). First instar larvae of M. vitrata at levels 0 (no larvae were released), 5, 10, 15, 20, 25 and 0, 25, 50, 75, 100, and 125 were used to infest (SAMPEA 7) cowpea at flower bud initiation, 50 % flowering and 50 % podding in both screen house and field cages, respectively. The treatments were arranged in a Complete Randomized Design (CRD) and Randomized Complete Block Design (RCBD) replicated four times for screen house and field trials, respectively. Parameters assessed include, number of pods produced, damaged pods, weight of grains and the rate of association between larval density and grain weight. The result obtained showed decreased yield in cowpea with increase in number of larvae infested in both screen house and field cages. Infestation with 5 and 25 larvae per cage, caused decrease in yield from 549.75 kg ha-1 and 843.50 kg ha-1 in screen house while infestation with 25 and 125 larvae caused a decrease of 486.25 kg ha-1 and 222.50 kg ha-1 in field cages. The estimated Economic Injury Levels (EIL) in the screen house was 0.13, 0.14, 0.14, 0.13 and 0.15 when Cypermethrin, Dimethoate, Chlorpyriphos, Cypermethrin plus Dimethoate and Imidachloprid, respectively were sprayed to control Maruca. The corresponding values for field cages were 0.14, 0.15, 0.14, 0.14 and 0.16, for the respective insecticides. Twelve cowpea varieties were also assessed for resistance to Maruca vitrata using three sowing dates at two weeks interval. The experiments were laid out in Randomized Complete Block Design (RCBD) replicated three times. Based on the percentage pod damage, damage score for each variety was given resistance rating 1-5. The results showed that the first sowing date (early August) had less infestation by M. vitrata and differed significantly (p<0.05) from those sown in late August to early September. All the varieties sown early August to late August had less Maruca infestation and produced higher grain yields than those sown early September. Wild cowpea (Vigna dekendtiana) was highly resistant and differed significantly (P< 0.05) from the cultivated varieties, while SAMPEA 1, 4, 6, 9 and 10 were the most susceptible varieties with higher pod and seed damage and lower grain yields. SAMPEA 7, 8, 11, 12, 14, and15 were moderately resistant. None of the variety was resistant or highly susceptible to the Maruca vitrata attack. Therefore, highly resistant and moderately resistant varieties can be utilized by the farmers and in breeding programme for the management of pod borer as a component of IPM.

 

 

TABLE OF CONTENTS

Title page ………………………………………………………………………………………………………………….. i Declaration ……………………………………………………………………………………………………………… ii
Certification ……………………………………………………………………………………………………………. iii
Dedication ……………………………………………………………………………………………………………….. iv
Acknowledgement …………………………………………………………………………………………………….. v
Abstract …………………………………………………………………………………………………………………. vii Table of Contents…………………………………………………………………………..viii List of Tables ………………………………………………………………………………..xi List of Figures……………………………………………………………………………….xii CHAPTER ONE:
1.0 INTRODUCTION ………………………………………………………………………………………….. 1
1.1 Justification ……………………………………………………………………………………………………. 3
1.2 Objectives ……………………………………………………………………………………………………… 4
CHAPTER TWO:
2.0 LITERATURE REVIEW ………………………………………………………………………………… 5
2.1 Origin and Distribution of Cowpea …………………………………………………………………… 5
2.2 Importance and Uses of Cowpea ………………………………………………………………………. 6
2.3 Constraints of Cowpea Production ……………………………………………………………………. 7
2.4 Insect Pests of Cowpea ……………………………………………………………………………………. 8
2.5 Legume Pod Borer, Maruca vitrata (G.) Fab. …………………………………………………….. 9
2.5.1 Nature of damage of Maruca vitrata …………………………………………………………………. 9
2.5.2 Host range and suitability ………………………………………………………………………………. 10
2.5.3 Life cycle …………………………………………………………………………………………………….. 10
2.6 Economic Injury Levels (EIL) ……………………………………………………………………….. 11
2.7 Management of Maruca vitrata on Cowpea …………………………………………………….. 12
2.7.1 Cultural practices: …………………………………………………………………………………………. 12
2.7.2 Insect resistant cowpea varieties: ……………………………………………………………………. 13
2.7.3 Use of biopesticides ………………………………………………………………………………………. 13
2.7.4 Use of synthetic insecticides ………………………………………………………………………….. 14
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CHAPTER THREE
3.0 MATERIALS AND METHOD ……………………………………………………………………… 16
3.1 Study Area …………………………………………………………………………………………………… 16
3.2. Mass Rearing of Maruca vitrata for Field and Screen House Infestation ……………………………………………………………………………………………………. 16
3.3 Experiment I: Determination of Economic Injury Level in the Field ……………………………………………………………………………………………………………. 17
3.3.1 Field establishment of crop ……………………………………………………………………………. 17
3.3.2 Maruca larvae infestation ………………………………………………………………………………. 19
3.3.3 Damage assessment and data collection …………………………………………………………… 19
3.4.0 Experiment II: Determination of Economic Injury Level under the Screen House Condition ………………………………………………………………………….. 20
3.4.1 Colony establishment …………………………………………………………………………………… 21
3.4.2 Calculation of economic injury levels ……………………………………………………………… 21
3.5.0 Experiment III: Field Evaluation of Cowpea Varieties for Resistance to M. vitrata ………………………………………………………………………………… 21
3.5.1 Field establishment and experimental layout …………………………………………………… 22
3.5.2 Data collection ………………………………………………………………………22 3.5.3 Data analysis……………………………………………………………………… …23 CHAPTER FOUR
4.0 RESULTS …………………………………………………………………………………………………….. 25
4.1.1 Effect of M. vitrata larvae infestation on number of pods produced, pods damaged, percentage pods damage and grain yield per cage in 2014 at Samaru…………………………………… ……………………25 4.1.2 Effect of M. vitrata larvae infestation on Healthy grain, damaged grains, percentage grain damage and 100 seeds per cage of cowpea in 2014 at Samaru.………………………………………………………25 4.2.1 Effect of M. vitrata larvae infestation on produced flowers, damaged flowers, produced pods and damaged pods per cage
of cowpea under screen house………….…………………………………………..28
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4.2.2 Effect of M. vitrata larvae infestation on percentage pods damage, Grains yield, damaged grain weight and percentage grain damage per cage of cowpea under screen house…………………………………………….30 4.3 Economic Injury Levels (EILs)…………………………………………………….30 4.4.0 Evaluation of some cowpea varieties for resistance to Maruca vitrata infestation ………………………………………………………..32 4.4.1 The effect of M. vitrata larval population and pods produced at three sowing date………………………………………………………………………32 4.4.2 Effect of M. vitrata infestation on damaged pods number and total grain weight (g) at three sowing dates of cowpea…………………………….….39 4.4.3 Effect of M. vitrata infestation on weight of grains damaged and 100 seed weight of cowpea per plot. …………………………………………..41 4.4.4 Effect of M. vitrata infestation on percentage grains damage and grain weight (kg ha-1) at three sowing dates of cowpea. …………..……………………43 4.4.5 Effect of M. vitrata infestation on percentage pods damage at three sowing dates of cowpea …………………………………………………………………….43 CHAPTER FIVE
5.0 DISCUSSION………………………………………………………………………47
5.1 Evaluation of some Cowpea Varieties for Resistance to Maruca Pod Borer………51 CHAPTER SIX
6.0 SUMMARY, CONCLUSION AND RECOMMENDATIONS………………….58
6.1 Summary……………………………………………………………………………58
6.2 Conclusion………………………………………………………………………….58 6.3 Recommendations………………………………………………………………….60 REFERENCES……………………………………………………………………………61 APPENDICES……………………………………………………………………………72

 

 

CHAPTER ONE

1.0 INTRODUCTION
Cowpea (Vigna unguiculata (L.) Walp) is an important grain legume in the tropics and subtropics. It is native to central Africa and belongs to the family Fabaceae (Cobley, 1956). More than 14.5 million hectares of land is planted to cowpea worldwide each year. Its global production as dried cowpea in 2013 was 6.2 million metric tonne, of which 94 % is in Africa (Diouf, 2011; FAOSTAT, 2014). Nigeria is the world largest cowpea producer where about 2.9 million metric tonnes are produced per annum, followed by 1.3 and 0.2 million metric tones of Niger and Mali, respectively (FAOSTAT, 2014). The major areas of production in Africa are Nigeria, Niger, Mali, and Senegal in West Africa, Cameroon and Democratic Republic of Congo in central Africa and Kenya, Sudan, Tanzania, Uganda and Somalia in East Africa (FAOSTAT, 2014). Under sole cropping, the grain yield potential of the crop ranges from 1.5-3.0 tonnes per hectare but can be realized mainly when insecticides are applied (Olufajo and Singh, 2002). In Nigeria the highest production of cowpea comes from the northern states of Nigeria where about 1.7 million tonnes from 4 million hectares have been reported (Anonymous, 2009). However, some appreciable quantities are also produced in the rainforest belt particularly in the South East of Nigeria (Oparaeke, 2004). Cowpea can be regarded as vegetable meat due to the high amount (20-30 %) of protein in the grain. It is thus a source of cheap plant protein to people who hardly can afford animal protein derived from meat, fish, milk and eggs (Olakoja at al., 2007, FAOSTAT, 2011). It is rich in minerals, fats, oils and vitamins and is consumed in different forms, with many local variations in their preparation (Gungula and Garjila, 2005).
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According to statistics, 52 % of Africa’s production is used for food, 13 % as animal feed, 10 % for seed, 9 % for other uses and 16 % is wasted (FAOSTAT, 2011). Most frequently, they are cooked together with vegetables, spices and often palm oil to produce a thick bean soup, which accompanies the basic staple foods, such as cassava, yams and plantain (Valenzuela and Smith, 2002). They are also ground into flour and mixed with sliced onion, spices and made into cakes, which are either deep-fried (akara balls), or steamed (moi-moi) in Nigeria (USAID, 2008). Cowpea is usually preferred by farmers because of its role in increasing soil fertility through nitrogen fixation and production of nutritious fodder for livestock (Blade et al., 1997; Singh, 2000). In Nigeria, farmers who cut cowpea fodder and store for sale during the peak of the dry season can obtain as much as 25 % of their annual income by this means (FAOSTAT, 2011). Insect pests are considered to be responsible for reduction in yield. Sometimes total yield loss and crop failure occur due to the activities of a wide spectrum of insect pests which ravage the crop in the field at different growth stages (Singh and Ajeigbe, 2002). Insects attack cowpea and cause economic damage at all stages of plant growth starting from seedlings to harvest and in storage. The major insect pests which severely damage cowpea at all growth stages are the cowpea aphid (Aphis craccivora Koch), foliage beetle (Ootheca mutabilis Sahlb), the flower bud thrips (Megalurothrips sjostedti Trybom), the legume pod borer (Maruca vitrata Fabricius) and the sucking bug complex, of which Clavigralla tomentosicollis Stal, Giant pod bug (Anoplocnemis curvipes F,) and Shield bug (Aspavia armigera L,) are prevalent and the most important. M. vitrata is a major pest of cowpea which causes economic damage at the lowest population density (Sharma, 1998).
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Jackai (1982) observed that infestation starts from the shoot of cowpea 21 days after planting and spread to productive parts. Intensity of larvae is usually highest on flowers followed by flower buds, terminal shoots and pods. M. vitrata can be controlled primarily through the use of chemical insecticides (Akinfenwa, 1975; Dina and Medaigedu, 1988). However, continous use of chemicals may lead to problems such as development of pest resistance, outbreak of secondary insect pests and pesticide residues in the produce and environmental degradation. Where the insect resistance develops the use of insect resistant genotypes is an important and compatible component of integrated pest management (IPM). Pedigo (2004) reported that IPM modules can be used as an effective, cheap, and environmentally safe method of reducing the menace of this pest. Reasonable grain yield cannot be obtained without proper management strategy (Jackai and Daoust, 1986; Amatobi, 2007). According to Stern et al. (1959), economic injury level (EIL) is the level at which damage can no longer be tolerated and therefore at that point or before reaching that levels deliberate control operation should be initiated.
1.1 Justification
Cowpea production in Sub- Sahara Africa accounts for more than 94 % of the world production (FAOSTAT, 2011). Tropical infestation by M. vitrata alone can cause yield loss reduction of 20-80 % (Singh et al., 1990; Sharma, 1998). Depending on the region and management practices, the year to year crop losses and challenges in effective field control have led to the identification of this pest as a major threat to economic and well-being of people in the developing nations. In West Africa, M. vitrata is one of the major pests of cowpea, especially in Nigeria, Niger and Mali, which are the major cowpea producing
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areas. A seasonal variation in yield losses that was obtained from Nigeria ranged from 48-86 % (IITA, 1986, Dryer et al., 1994). The high population of Maruca encountered on cowpea leads to expensive control measures. Their typical feeding habit makes control of the larvae so difficult with pesticides and their natural enemies. Farmers usually spray insecticides to protect the cowpea crop from Maruca and other pests. Cost of chemicals, added to the production cost, thus reducing the farmer’s profit. The development of cowpea resistant to Maruca and other insect pests would benefit the most resource poor African farmers who grow the crop. The basic biology of M. vitrata has been studied extensively (Jackai 1982; Akinfenwa, 1975; Singh et al.,1990), but there is still inadequate information on the level at which they caused damage on cowpea in Nigeria and this could hinder the development of effective integrated pest management strategies against the pest in the country. Economic injury level is prerequisites of IPM and basic criterion to knowing the need and time to apply economic control measures (Smith, 1968). Transgenic plants and traditional plant breeding for insect resistant varieties are potentially effective methods for managing pests of cowpea, a better understanding of pest populations is needed in order to integrate these, and other pest control options into an overall integrated pest management (IPM) plan to maximize cowpea production in the field.
1.2 Objectives
The present research work was undertaken to:
i. Determine the economic injury levels of Maruca vitrata on cowpea
ii. Evaluate some cowpea varieties for resistance to the Maruca pod borer.

 

 

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