Foliar insect pest management on cowpea (Vigna unguiculata Walpers) in simulated varietal mixtures II. Pest resistance management implications

Field experiments were established in which cowpea (Vigna unguiculata Walpers) was treated with a series of partial insecticide (carbofuran) application treatments to simulate (susceptible/resistant) varietal mixtures and a series of inter-crops with soybean (Glycine max). Treatments were sampled for damage by the foliage pests Ootheca mutabilis Sahlberg and Aphis craccivora Koch and for flower production. The soybean is likely to have provided both a mechanical barrier to pest movement and disruption to O. mutabilis through volatile allelochemicals. The comparison between the two treatment types would suggest whether similar mechanisms were the cause of pest reductions observed in partial insecticide applications on cowpea. The results suggested that the inter-cropping with soybean was not as effective in managing pest populations as a partial insecticide application and could even increase pest numbers. Further examination of the data from the partial insecticide application treatments appeared to show that the pest infestation was lower on the untreated plants closest to the insecticide-treated plants. This could be as a result of pest redistribution onto insecticide-treated plants after initial colonisation. The implications of this, in terms of pest resistance management are discussed.