Abstract Three strains of Callosobruchus maculatus (F.), from Brazil, Nigeria and the Yemen Arab Republic, do not survive equally well or develop at the same rate in a resistant cultivar of cowpea, TVu 2027. First generation hybrids between them survive and develop at rates intermediate between those of their parents but generally nearer the level attained by the more successful or tolerant parental strain. The indication is therefore that resistance to antimetabolites in TVu 2027 in inherited as a dominant characteristic. Breeding of the Yemen and Nigerian strains on TVu 2027 for 3 generations demonstrated that the performance of the beetles rapidly improves in terms of both survival and developmental rate. It is concluded that the useful lifespan of TVu 2027 and its hybrid progeny, in respect of bruchid resistance, is probably very limited. The selection pressure imposed by its use would probably lead rather rapidly to the evolution of beetle populations capable of surviving in large numbers and spreading their resistant capacities through hybridization to other adjoining populations.