Overview

Trials were conducted at the Technology Verification Centre (TVC), Bukedea, Kumi district, during the first rains of 2003A, to determine the effect of cowpea cropping systems and insecticides on the abundance and diversity of predator and parasitoid arthropods in Eastern Uganda. In addition, the effectiveness of generalist predators (earwigs and syrphid flies) on aphids was evaluated through laboratory and on-field cage experiments. Parasitism of cowpea aphids was low (0.1-8.5%). Tachnidae (Diptera) and Aphidius (Hymenoptera) parasitoids were mostly recovered with relative abundance varying with cropping seasons. The insecticides significantly reduced the population density of natural enemies. The abundance of different predators was considerably affected by the cowpea cropping system, the time of sampling, and the level of insecticide spray. Beneficial arthropod biodiversity loss was critical with the recommended dose (Cypermethrin+dimethoate) of application. Population densities of predators, were higher in cowpea polycultures than in monocultures. In cage experiments, it was observed that a syrphid larva was able to consume 1-4 aphids daily while in the laboratory, it could consume around 5-6 aphids daily. Syrphids need to be integrated in IPM systems to control aphid populations in major cowpea cropping systems where aphids appear to be a serious constraint.