Effects of cowpea cropping systems and insecticides on arthropod predators in Uganda and Democratic Republic of the Congo

Knowledge of the distribution, abundance, species diversity and effectiveness of indigenous natural enemies of cowpea pests in Uganda and the Democratic Republic of the Congo (DRC) is poor. Similarly, effects of insecticides commonly used by cowpea farmers on arthropod predators are not well documented in these countries, so effects of insecticides on these natural enemies were monitored in field trials with cowpea grown solely and in association with sorghum or greengram. The abundance of predators (Coccinellidae, Staphylinidae, Syrphidae, Anthocoridae, Mantidae, Dermaptera, ground beetle, predatory mite, lygaeid bugs, Anthocoridae, dragonflies and spiders) were considerably affected by insecticides and the cropping system. Polyculture had a higher index of diversity than monocultures. In terms of species diversity supported, there was no significant difference between cowpea/greengram and cowpea/sorghum. There was a seasonal variation in similarity (MS=0.71, long rains; MS=0.77, short rains) of the predator community supported by the cowpea cropping system, between Mulungu (DRC) and Kumi (Uganda) habitats. Lower pests pressure on cowpea crop, higher abundance of predators and higher cowpea yields were observed to be associated with cowpea/greengram cropping systems. Therefore cowpea/greengram should be promoted among other biological control conservation strategies, aiming at enhancing natural enemies in cowpea systems, through habitat manipulation. This study indicated that generalist predators, through their activities might be important natural enemies of cowpea pests in Uganda and in DRC.