ABSTRACT.1The eggs of the cowpea seed bettleCallosobruchus maculatus(Fab.) are attached to cowpeas. On hatching, the larvae penetrate the testa and remain in the seed until development is complete and adult eclosion has occurred. The adults do not need to feed and were not allowed to do so.2Strains from Brazil and Nigeria can produce more than twelve adults from a seed bearing numerous eggs, whereas a strain from the Yemen Republic rarely produced more than three.3In all three strains the mean weight of the adults produced from a single cowpea declined with increasing initial larval density in the seed.4Egg production by females is positively correlated with their weight at the time of mating, shortly after emergence.5Lifetime egg production by females of the Brazilian and Nigerian strains was lower if they came from cowpeas with higher initial larval densities. No such relationship could be demonstrated in the Yemen strain.6The fecundity of one generation of these beetles, at least in some geographical strains, is significantly affected by the number of larvae entering the hosts in which the adults of that generation have developed.