Resistance to Callosobruchus maculatus (Coleoptera: Bruchidae) in Selected Cowpea Lines

Four high-yielding lines of cowpea, Vigna unguiculata (L.) Walp., were evaluated for resistance to four geographic strains of the cowpea weevil, Callosobruchus maculatus (F.). Unlike the low-yielding accession from which they were derived, the four advanced lines did not cause high mortality of C. maculatus larvae within seeds. Resistance to larvae was expressed solely as delayed growth. Variation among beetle strains was minor, although the Nigerian strain appeared to develop faster than the others did on resistant seeds. Development times in all populations decreased slightly or not at all after six generations of selection favoring the fastest-developing beetles. Females reared on resistant seeds were as fecund as those reared on susceptible seeds. The resistant cowpea lines differed from each other mostly in the acceptability of seeds for oviposition; two rough-seeded lines combined antibiosis resistance to bruchid larvae with nonpreference resistance to ovipositing adults