The proportion of the “active” form of the cowpea weevil,Callosobruchus maculatusF., among a population emerging from infested cowpeas in the laboratory is greatly reduced in small seeds. It is replaced by a “miniature” form of the weevil. The factors conditioning production of the “active” form appear to operate when sufficient food is supplied.Small-seeded varieties would have a limiting effect on population increase of the weevil. However, breeders have to select cowpeas for a size acceptable to consumers and, in addition, for intrinsic characteristics conferring resistance to the cowpea weevil, preferably a deterrent seed coat and/or reduced nutritional value to the weevil. Frequency of miniature forms deserves attention as a more dependable parameter than that of the active form in rapid screening of large numbers of entries for sources of resistance.