ABSTRACT

Cowpea is cultivated as a commercial and home garden crop in dry zone and intermediate
zone. Many species of insects are associated with cowpea and they are generally
managed by applying insecticides. Insecticide application has many negative
consequences. Hence, there is an interest among farmers to have alternate strategy for
cowpea pest control. Farmers traditionally use plant based mixtures but lack scientific
evidences on its efficacy. Hence, this study examines the efficacy of selected plant based
mixtures to manage cowpea pest populations under field conditions.

Neem (Azadirachta indica) seed kernel water extract (NSKWE), Cow dung + Herbal
(CDH) mixture, Wood Ash + Kerosene oil mixture (WAK) and Araliya (Plumeria
odusta) flower water extract (AFWE) were sprayed on cowpea at weekly intervals and
plots were laid as RCBD. Insect populations were assessed using standard sampling
techniques and crop damage, crop growth and yield were also assessed.

All the mixtures significantly reduced foliar and pod damage compare to unsprayed
control. The highest pod damage reduction (85.6 %) compared to control was in
NSKWE. The highest yield (17.6 g of seeds / plant) was recorded in NSKWE. Aphid
level was lowest in the NSKWE four times compared to the control. Pod borer
populations and Plant Bug populations were lowest in the NSKWE.

Ground dwelling insects, particularly carabids were not significantly affected by any of
the application but there was a significant variation of hymenopterans, mainly parasitoids,
among treatments. Lowest hymenopteran population was found in the AFWE.

Laboratory bioassay tests were conducted to assess efficacy of mixtures. LD50 values of
CDH and AFWE were and 13.27 % and 32.10 % of stock solution respectively.

These results indicate that NSKWE, CDH and AFWE have different efficacies in
controlling insect pests but these mixtures are good alternates for traditional insecticides.

Key words: Cowpea pests, Botanicals, Natural insecticides, Neem seed kernel extract

   

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 ACKNOWLEDGEMENT

It is with deepest sense of gratitude to my supervisor Dr. K. S. Hemachandra, Senior

Lecturer, Department of Agriculture Biology, University of Peradeniya for his
tremendous encouragement, excellent guidance and supervision extended to me
throughout the research study to make it success.

Also I would like to my sincere gratitude to my co supervisor, Prof. W. A. P.

Weerakkodi, Senior Lecturer, Department of Crop science, University of Peradeniya for
his immense support given to me in succeeding my study.

I wish to acknowledgement Prof. Daya Ahangama, Head of the department, Department

of Agriculture Biology, University of Peradeniya for giving me an opportunity and
facilitates to carry out my research project successfully.

I extend my thanks to Mr. Nimal Amarasiri, Farm manger, Agriculture experimental

farm, Dodangola for facilitating this research opportunity, and invaluable support given
during this research project also my special thanks go to Mr. Amarakoon and others in the
Dodangolla farm for their excellent support during research project period.

Finally, my warm gratitude goes to my loving farther and all my teachers and friends.

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 TABLE OF CONTENTS

Abstract i

Acknowledgement ii

Table of contents iii

List of tables vii

List of figures viii

List of Plates ix

Chapter one

Introduction 1

Chapter 02

Review of Literature 4

2.1 Legumes 4

2.1.1 Symbiotic behavior of legumes 4

2.2 Cowpea 5

2.2.1 Importance of the cowpea crop 5

2.2.2 Cowpea: Botany of cowpea 6

2.2.3 Morphological characters of cowpea 6

2.2.4 Cowpea production of the world 6

2.2.5 Cowpea cultivation in Sri Lanka 7

2.2.6 Nutritive value of the crop 8

2.2.7 Toxic constituent of cowpea 8

2.2.8 Cultivation requirements of cowpea 10

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 2.3 Insect pests of cowpea 11

2.3.1 Cowpea Aphid (Aphis craccivora) (Aphididae) 11

2.3.2 Bean fly (Ophomia phaseoli) (Agromyzidae) 12

2.3.3 Legume pod borer (Maruca testulalis) (Pyralidae) 12

2.3.4 Pod sucking Bug (Leptoglossus australis) (Coridae) 13

2.3.5 Blue butterfly (Lampides boeticus) (Lycaenidae) 13

2.4 Pest control strategies 15

2.4.1 Chemical control 15

2.4.1.1 Negative impacts of chemical control 15

2.4.2 Resistant varieties 15

2.4.3 Biological control 16

2.4.4 Cultural practices 16

2.5 Botanical insecticides (plant based mixtures/extracts) 16

2.5.1 Current use of Botanicals (plant based mixtures/extracts) 17

2.5.2 Properties of Botanicals (plant based mixtures/extracts) 18

2.5.3 Common plant based mixtures/extracts 18

2.5.3.1 Neem (Azadirachta indica) 18

2.5.3.2 Temple trees (Plumeria obusta) 20

2.5.4 Other pest control products 20

2.5.4.1 Cow dung and cow urine mixtures 20

2.5.4.2 Wood ash 21

2.6 Use of botanical insecticides for a control of insect pests 25

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Chapter 3

Materials and methods 28

3.1 Research Location 28

3.2 Land preparation 28

3.2.1 Setting of field layout 28

3.3 Planting 29

3.4 Experimental design 29

3.5. Preparation of mixtures for insect control 30

3.5.1 Neem seed kernel water extract 30

3.5.1 Organic mixture 30

3.5.3 Wood ash, kerosene mixture 30

3.5.4 Araliya flower water extract 30

3.6 Treatment application 31

3.7 Data collection 32

3.7.1 Installation of sampling equipments 32

3.7.2 Installation and data collection of Pit fall traps 32

3.7.3 Installation and data collection of Sticky traps 33

3.7.4 Installation and data collection of Water Pan traps 34

3.7.5 Other data 34

3.8 Laboratory Bioassay 35

3.9 Data Analysis 35

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Chapter 4

Results and discussion 36

4.1 Insect pest incidence in cowpea 36

4.1.1 Bean fly 36

4.1.2 Aphids 36

4.1.3 Foliage damage 38

4.1.4 Pod damaging insects 39

4.2 Incidence of natural enemies 41

4.2.1 Ground beetles (Family: Carabidae) 41

4.2.2 Parasitic Hymenoptera (Family: Brachonidae) 42

4.3 Plant growth 43

4.3.1 Height of the plant 43

4.3.2 Leaf area index 43

4.4 Yield 44

4.5 Laboratory bioassay 47

Chapter 5

Conclusion and suggestions 49

5.1 Conclusions 49 

List of references 50

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 LIST OF TABLES

Table 2.1 Production of Cowpea in Sri Lanka: (2003-2009) 7

Table 2.3 Chemical composition of some common pulse legumes 9

Table 2.3 Nutritional value of different products of cowpea 9

Table 2.4 Amino acid composition of cowpea 10

Table 2.5 Insect pests attacking cowpea in Asia 14

Table 2.6 Some of commonly used and popular plant based mixtures 22

Table 2.7 Active ingredients and mode of action of neem 19

Table 4.1 Difference of different insect numbers caught in various traps

before and after the application of plant based mixtures/extracts 40

Table 4.2 Difference of hymenopteran insect numbers caught in sticky traps

before and after the application of plant based mixtures/extracts 42

Table 4.3 Yield data of cowpea treated with four different

plant based mixtures/extract 46

Table 4.5 Regression equation and correlation for the

Cow dung + herbal mixture and Araliya flower water extract

on mortality of A. craccivora after 16 hours 47

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 LIST OF FIGURES

Figure 3.1 Layout of the research trial 29

Figure 3.2 Installation of sampling equipments 32

Figure 3.3 Installation of Pit fall trap 32

Figure 3.4 Installation of Sticky trap 33

Figure 3.5 Installation of Sticky trap 34

Figure 4.1 Effect of plant based mixtures/extracts on Hemipterans caught by

sticky traps on cowpea at Dodangolla experimental farm, 2010 37

Figure 4.2 Effect of plant based mixtures/extracts on aphid colonization on

cowpea at Dodangolla experimental farm, 2010 37

Figure 4.3 Effect of plant based mixtures/extracts on leaf damage on

cowpea at Dodangolla experimental farm, 2010 38

Figure 4.4 Effect of plant based mixtures/extracts on pod sucking bugs on

cowpea at Dodangolla experimental farm, 2010 39

Figure 4.5 Variation of mean number of Carabid beetles per plot

caught using pitfall traps among treatments 41

Figure 4.5 Variation of mean height of plant with time in plants

treated with various mixtures/extracts 44

Figure4.6 Log concentrations – Log mortality response curve of Araliya

extract and cow dung + herbal mixture against A. craccivora 47

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 LIST OF PLATES

Plate 3.1 Polythene cover used for the separate plots of the research trial

conducted at Dodangolla experimental station 31

Plate 4.1 Comparison of Yield of cowpea treated with four different

plant based mixtures/extract at Dodangolla experimental farm 45

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