Synergistic control of Callosobruchus maculatus Fab. (Coleoptera: Chrysomelidae) by releases of an oophagous and a larval parasitoid in experimental cowpea storage systems
Callosobruchus maculatus Fab. (Coleoptera: Chrysomelidae) is a major pest of stored cowpea in West Africa, responsible for significant weight losses and grain deterioration during storage. Biological control of this pest using its native larval (Dinarmus basalis) and oophagous (Uscana lariophaga) parasitoids is currently investigated. The present study aims to assess into experimental storage systems the effects of five options of releasing U. lariophaga and D. basalis, alone or in combination, on the populations of C. maculatus in comparison with a control without any parasitoid. The combined releases of the two parasitoid species prevented the increase in C. maculatus numbers better than the release of a single parasitoid species. Each parasitoid species behaved differently when alone versus in combination. Thus, D. basalis had a higher development and rates of parasitism when it was alone, whereas the opposite was observed in U. lariophaga, whose parasitism activity seemed to be stimulated by the presence of D. basalis. After 150 days of storage, the cowpea seed losses were estimated to be significantly lower (9–13%) in all parasitoid combination treatments instead of 31% and 62% in single parasitoid treatments and the control, respectively. Our results suggest that combined releases of both parasitoids can additively control the pest and maintain cowpea quality over 5 months of storage. Further studies should precise the optimal densities of each species to be released without additional introductions throughout the storage period. Interactions between D. basalis and U. lariophaga are still poorly known and will require in-depth scientific investigations.