Potential of five wild legume species as alternative rearing substrates of Uscana lariophaga Stef. (Hymenoptera: Trichogrammatidae), a promising biocontrol agent of Bruchids pest of cowpea in West Africa

Abstract

Callosobruchus maculatus (Coleoptera: Chrysomelidae, Bruchinae) is the major pest of stored cowpeas in West Africa. Biological control using its egg parasitoid Uscana lariophaga Stef. (Hymenoptera: Trichogrammatidae) is currently under investigation but faces limitations due mainly to the difficulty of mass production. Research was conducted under laboratory conditions to evaluate the suitability of five wild legume seeds for Callosobruchus maculatus Fab. and its egg parasitoid rearing in comparison to two varieties of Vigna unguiculata, (KXV 61-1 and Local Moussa) used as control host plants. The seeds of the wild legumes physically described using texture, weight, size and color were different from cowpea seeds. The analysis of C. maculatus oviposition in no-choice experiments showed that eggs were laid on all the legume seeds tested. However, the wrinkled cowpea seeds were more infested (77.50±2.89 eggs) than the wild legumes smooth seeds, the lowest mean number of eggs (9.15±0.98) being observed on A. gourmaensis flat seeds. Regarding the reproductive potential of U. lariophaga, the eggs of C. maculatus laid on all the five wild legumes may be parasitized and allow the development of the progeny of the parasitoid. Based on the intrinsic rates of natural increase, three wild legume species (A. nilotica, A. gourmaensis and A. macrostachya) allowed a development of U. lariophaga equivalent to that obtained with the seeds of the cowpea varieties used. Our results provide a basis for the development of a method of mass production of the egg parasitoid U. lariophaga using the most promising wild legumes on which future research is expected to intensify.