Natural suppression of bruchid pests in stored cowpea<i>(Vigna unguiculata</i>(L.) Walp.) in West Africa

Abstract

Abstract Stored cowpea was collected from village storage units and from a market in Niger, to study the occurrence of bruchid pests and their parasitoids. High variability in storage methods and structures and in the levels of bruchid and parasitoid attack was observed. The village of origin, the cowpea variety and the type of storage structure all had significant effects on the percentage of beans attacked by bruchids. Damage to beans was highest in the Northern Ouallam region, and parasitism was highest in the South near Say. Bruchid eggs parasitized by Uscana spp. were present in 69% of all samples. Emergence holes and adults of larval parasitoids (Eupelmus spp. and Dinarmus spp.) were found in 92% of all samples. Some samples with high levels of egg or larval parasitism showed the potential for natural control, given the right conditions. Storage units seem to function as isolated units with little dispersal between them. The use of insecticides seems to decrease the impact of parasitoids, leading to higher bruchid populations and losses. Comparing the results from this survey with the outcome of interviews with farmers in Nigeria and Niger, it appears that traditional storage methods and protection techniques are gradually disappearing.