Insect Pests of Cowpeas Vigna Unguiculata(L.)
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\\ INSECT PESTS OF CCWPEAS VIGNA UNGUICULATA (L.) WALP. AND STUDIES ON COWPEA YIELD ASSESSMENT UNDER DIFFERENT CHEMICAL SPRAY REGIMES AND MINIMUM USE OF INSECTICIDES AGAINST THE DOMINANT INSECT PEST SPECIES AT KATUMANI DRYLAND RESEARCH STATION, KENYA • By FLORENCE R.A.|mABONGA p.r.EN accepted foe 1HI8 THESIS n \<2 ...... i h e d e g r f f t £KL> A Ci'.PV p {~ i LACED TUB* JMUVEBSI'XV LiUUARY A thesis submitted in partial fulfilment for the Degree of Master of Science in the University of Nairobi. DECLARATION BY CANDIDATE This is my original work and has not been presented for a degree in any other University. F.R.A. Mabonga DECLARATION BY SUPERVISOR This thesis has been submitted for examination with my approval as University Supervisor. Professor Canute P.M. Khamala 111 TABLE OF CONTENTS Page TITLE ............................................. i DECLARATION........................................ii TABLE OF CONTENTS................................iii LIST OF TABLES...................................vii TEXT OF FIGURES.................................. x LIST OF PLATES...................................xii ACKNOWLEDGEMENTS.................................xiv ABSTRACT...........................................xv CHAPTER 1 GENERAL INTRODUCTION AND OBJECTIVES, LITERATURE REVIEW AND GENERAL MATERIALS AND METHODS ............................ 1 1.0 GENERAL INTRODUCTION AND OBJECTIVES.......................... 1 1.10 LITERATURE REVIEW................... 4 1.20 GENERAL MATERIALS AND METHODS.... -.17 CHAPTER 2 INSECT PESTS OF FIELD COWPEA CROP IN KENYA....................... 25 2.0 INTRODUCTION........................ 25 2.10 MATERIALS AND METHODS................25 2.20 RESULTS 27 2.21 List of Field cowpea Insect Pests,Plant Part Attacked and their Pest Status at Katumani Dryland Agricultural Research Station...................... 27 2.22 Brief Description of Common Feild Cowpea Insect Pests at Katumani Dryland Agricultural Research Station....................... 36 2.23 Relative Abundance of Common Major Cowpea Insect Pest Species during 1978 and 1979 short and long rainy seasons respectively................. 46 2.24 Seasonal Abundance of some of the Common major cowpea insect pest species at Katumani during short (1978) and long (1979) rainy seasons....................... 48 2.30 DISCUSSIONS........................ 62 V Page CHAPTER 3 DETERMINATION BY SEED YIELD ASSESSMENT OF THE MOST SUITABLE PERIOD TO APPLY INSECTICIDES ON SOLE CROP COWPEA FOR EFFECTIVE PROTECTION AGAINST INJURIOUS INSECT PESTS....................... 56 3.0 INTRODUCTION....................... 56 3.10 MATERIALS AND METHODS............. 58 3.11 Seed Yield Assessment....... 61 3.20 RESULTS AND DISCUSSION ............ 61 3.21 Effect of Spraying on flower and pod production............ 61 3.22 Influence of various insecticidal spraying regimes against insect pests on seed yields by ten cowpea varieties...................... 63 CHAPTER 4 DETERMINATION OF MINIMUM INSECTICIDAL USE FOR CONTROL OF THE DOMINANT COWPEA CROP INSECT PESTS WITH SPECIAL REFERENCE TO THE GROUNDNUT APHID APHIS CRACCIVQRA KOCH ............ 68 4.G INTRODUCTION...................... 68 VI Page 4.10 MATERIALS AND METHODS.......... 68 4.20 RESULTS AND DISCUSSION............. 70 CHAPTER 5 GENERAL DISCUSSION................. 75 REFERENCES............... :...................... 79 V 1 1 LIST OF TABLES Page Table 1. A list of Field Cowpea Insect Pests, Plant Part Attacked and their Pest Status at Katumani Dryland Agricultural Research Station............................ 29 Table 2. Relative Abundance of the common major Cowpea Insect pests at Katumani Dryland Agricultural Research Station during the 1978 and 1979 short and long rainy seasons respectively....... 47 Table 3A. Seasonal Abundance of the common major cowpea insect pest species at Katumani during short (1978) and long (1979) rainy seasons as shown by random stem, flower and pod sampling...................... 49 Table 3B. Seasonal Abundance of the common major cowpea insect pest species at Katumani during short (1973) and long (1979) rainy seasons as shown by sweep-net sampling...... 50 v i i i Page Table 4 Dates of planting, insecticide application and first harvest of cowpea at Katumani , Kenya, 1 978/79.................... 59 Table 5 Days to first flower appearance of 10 varieties of cowpea under different spray regimes at Katumani , 1979 ................... 62 Table 6 Seed yield performance by ten cowpea varieties grown during the short rains of 1978 at Katumani and treated with insecticide twice, at germination and at first flower appearance and with the control.... 64 Table 7 Seed yield performance by ten cowpea vari eties. grown during the long rains of 1979 at Katumani and •treated with insecticide four times at 14 days intervals from germin ation to 55 days after planting (D.A.P.) (Block A) (Pre-flowering); and from 55 to 97 D.A.P. (Block B) (Post-flowering), with the control..65 Table 8. Plant growth habit, dates of sampling, number of times sprayed and yields of the ten cowpea varieties studied at Katuraani during the short rains crop of 1978........................... Table 9. Plant growth habit, dates of spraying, number of times sprayed and yields of the ten cowpea varieties studied at Katumani during the short rains crop X TEXT OF FIGURES Figure 1 Field Layout of Experimental Plots and Subplots Figure 2a Wingless Adult of Groundnut aphid Aphis cracci vora Figure 2b Winged Adult of Groundnut aphid Aphis cracci vora Figure 2c Showing drawing of the Nycnph Groundnut aphid Aphis craccivora Figure 3a Drawing of Adult Callosobruchus maculatus Figure 3b. Antennae of Callosobruchus maculatus showing sexual dimorphism Figure 4a. Drawing of Adult Flower thrip Megalurothrips sjostedti Figure 4b Drawing of Nymph of the flower thri p "egalurothrips / sjostedti Figure 5 Field Layout of Plots for the Determination by Seed Yield Assessment of the Most Suitable Period to Apply Insecticides on Sole Crop Cowpea for li fetuvs protection Against Injurious Insect Pests xi Figure 6 Effect of insecticide applications on flowering patterns and flower production in ten varieties of cowpea Figure 7. Effects of insecticide app1icationson pod formation patterns and pod production in ten varieties of cowpea . LIST OF PLATES Plate 1. Adult Spiny Brown Coreid bug Acanthomia horrida showing characteristic pronounced thoracic spines Plate 2a. Mature Larva of cutworm Agrotis segetum Plate 2b. Male and Female Adults of cutworm A. segetum Plate 3 Male and Female Adults of Giant Coreid bug Anop1ocnemi s curvi pes Plate 4 Groundnut Aphid Aphi s ere cci vora on cowpea young shoots in the field at Katumani Plate 5a Straight cowpea pods before attack by the Groundnut Aphid Aphis craccivora in the field at Katumani Plate 5b Cowpea pods at initial stage of attack by the Groundnut Aphid Aphis cracci vora Place 5c. Second stage of attack of cowpea pods by Groundnut Aphid Aphis craccivora / Pods curve in severe attack Plate 6<j Aduit African uoiiworin ne \ i o ut i s a rm i ge r a at rest Plate 6b Mature Larva of African bollworm Heliothis o v»m ] nof 9 xi i i Plate 7 Adult beetle of Lagri a vi11osa i Plate 8a Showing mature larva of legume pod borer Maruca testulalis Plate 8b Showing characteristic wing markings on Legume Pod borer Maruca testu1 a 1is Plate 9 Nymph and Adult of Green stink bug Nezara vi ri du 1 a Plate 10 Showing Green stink bug Nezara vi ridula mating on cowpea crop in the field at Katumani xi v ACKNOWLEDGEMENTS This work was carried out at Katumani Dryland Research Station of the Ministry of Agriculture, Machakos District. I am grateful to the then Director of the station, Mr. A.M. Marimi, for the facilities put to my disposal. I am most grateful to the Federal Republic of Germany for granting me the scholarship (DAAD) that enabled me to carry out these studies. My special thanks go to my Supervisor, Professor C.P.M. Khamala, whose supervision and constant encouragement made the completion of this work possible. I wish tc express sincere gratitude to the entire- technical staff of Zoology Department especially Mr. N. Mwanga who solved my photographic problems. I am thankful to the staff of the National Agricultural Laboratories, Nairobi; the National Museums of Kenya, Nairobi; and Commonwealth Institute of Entomology, London, for their assistance in identification of many of my insect specimens. The typing talents of two ladies, Mrs. Ruth Watulo and Miss Martha Ndwiga enabled me to type both my scripts and final thesis. Most of all, I am grateful to members of my family especially my husband for their patience and enccurange iient. throughout the course of inv work. XV ABSTRACT Studies to identify major insect pests attacking cowpea, Vigna unguiculata (L.) Walp., in the field and to assess cowpea yields under different chemical control regimes were conducted at Katumani, Kenya during the short and the long rainy seasons of 1978 and 1979 respectively. From materials collected in unsprayed plots, the cowpea crop was found to be attacked by a total of 43 species of insects which were classified into seven orders: Diptera (1), Coleoptera (10), Heteroptera (15), Homoptera (3), Lepidoptera (8), Orthoptera (4) and Thysanoptera (2). Only a few of these were considered major pests, namely, Acanthomi a horri da Germ, A g r o 11s seqetum D and S, Anoplocnemis curvipes F., Aphis cracci vora Koch,. Cal 1 osobruchus macul at us Fab., Heli oth i s armi gera Hb , L a gr i a v i11 os a Fab., Maruca tes tula 1i s Geyer, Mega!urothri ps sjostedti Trybom, Nezara vi ri dula