NATURAL SUPPRESSION OF BRUCHID PESTS IN STORED COWPEA (VIGNA-UNGUICULATA (L) WALP) IN WEST-AFRICA

Stored cowpea was collected from village storage units and from a mark et in Niger, to study the occurrence of bruchid pests and their parasi toids. High variability in storage methods and structures and in the l evels of bruchid and parasitoid attack was observed. The village of or igin, the cowpea variety and the type of storage structure all had sig nificant effects on the percentage of beans attacked by bruchids. Dama ge 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 o f larval parasitoids (Eupelmus spp. and Dinarmus spp.) were found in 9 2% of all samples. Some samples with high levels of egg or larval para sitism showed the potential for natural control, given the right condi tions. Storage units seem to function as isolated units with little di spersal between them. The use of insecticides seems to decrease the im pact 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 storag e methods and protection techniques are gradually disappearing.