Insect pests of Cowpeas 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

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 attached by a total of 43 species of insects which were classified into seven orders: Diptera (1), Coleoptera (10), Heteroptera (4), Homoptera (3), Lepidoptera (8), Orthoptera (4), and Thysanoptera (2). Only a few of these were considered major pests, namely, Acanthomia horrida Germ, Agrotis segetum D and S, Anoplocnemis curvipes F., Aphis craccivora Koch, Callosobruchus maculatus Fab., Heliothis armigera Hb, Lagria villosa Fab., Maruca testulalis Geyer, Megalurothrips sjostedti,Trybom, Nezara viridula L. Maximum seed yields were obtained from cowpea plots sprayed with gamma BHC insecticide after flowing. There were no significant difference in yields between plots sprayed with insecticide before flowering and those of the untreated plots. Insecticidal treatments applied four times after flower at 14 days interval, starting at the appearance of first flowing, gave significantly higher yields than spraying two times after onset of flowering at 45 days apart. Mean seed yield of the ten varieties of cowpea used differed significantly between treated and untreated cowpea plots. The local varieties KAT 1, KAT 2 and KAK 1 constantly performed well producing higher yields than the exotic varieties except VITA 4. Aphids which were one of the most important pests of cowpea at Katumani preferred to colonize prostrate varieties to erect ones in growth habit. When gamma BHC insecticide was applied to plots attacked with aphids there was no correlation between insecticide application and cowpea varietal yields