Biological and Molecular Evidence for the Existence of Bruchid Ecotypes in the Nigerian Cowpea Ecosystem

Abstract

The oviposition, growth and development of six populations of Callosobruchus maculatus (IT, PH, UM, MD‐1, MD‐2, MD‐3) from different localities in Nigeria were studied on a resistant (TVu 2027) and susceptible (Ife Brown) cowpea cultivar and four cultivars of African yam bean, Progenies obtained by cross‐mating individuals from the different populations were also studied.. Oviposition was highest in the MD insect beetle population and lowest in the UM population. IT and PH populations had the highest adult emergence and shortest development times on the resistant control. Genomic differences among bruchid populations were confirmed by the Random Amplified Polymorphic DNA (RAPD) fingerprinting technique with PH population being the most distant. All progenies with IT as the female parent also had better emergence and shorter development time than their reciprocal crosses or those involving other populations, but this varied with the fitness of the male parent. The UM population averaged <10% adult emergence on TVu 2027 compared to 71.9 % on the susceptible control, but was better adapted to the AYB (66 % emergence) than were other populations. These results suggest possible existence of ecotypes, of this bruchid species in Nigeria with potentially important implications for the development and deployment of resistant cowpea varieties.