Impact of the egg parasitoid Uscana lariophaga and the larval-pupal parasitoid Dinarmus basalis on Callosobruchus maculatus populations and cowpea losses

In West Africa, Uscana lariophaga Steffan (Hymenoptera: Trichogrammatidae) and Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae) parasitize the eggs and larvae, respectively, of Callosobruchus maculatus Fab. (Coleoptera: Bruchidae), an important pest of stored cowpea. The impact of the parasitoids on pest populations was evaluated in clay pots similar to the ones used in traditional storage in Niger. At the beginning of the storage period, cowpeas were infested with one density of C. maculatus and with either one or both of the parasitoid species. If the parasitoids we inoculated as single species in stores, both D. basalis and U. lariophaga significantly suppressed the bruchid population, but the former did so more effectively than the latter. A combination of D. basalis and U. lariophaga resulted in the same suppression of bruchid populations as when D. basalis was the only parasitoid. Fifteen weeks after storage, the parasitoids reduced the number of grains damaged significantly by 38–56%. The effect of inoculating single or multiple parasitoid species on C. maculatus populations in an augmentation strategy is discussed.