Main content area

How Southern Cowpea Weevil Larvae (Bruchidae: Callosobruchus Maculatus) Die on Nonhost Seeds

Janzen, Daniel H.
Ecology 1977 v.58 no.4 pp. 921-927
Callosobruchus maculatus, Curculionidae, Delonix regia, Parkinsonia aculeata, Rhynchosia, Schizolobium, adults, cowpeas, eggs, hardness, larvae, seed coat, seeds, toxicity
Callosobruchus maculatus bruchids (southern cowpea weevils) oviposited on the seed coats of 63 species of nonhosts in the laboratory. The first—instar larvae were unable to penetrate the seed coats of 17%, made a shallow pit in 30%, made a deep pit in 13%, and passed through the seed coats of the remaining 41%. Even when the seeds were cut in half, so that the eggs were laid directly on seed contents, the larvae died very shortly after mining into the seed contents of 92% of the 63 species. In only 1 case (Rhynchosia calycosa) did the bruchid develop normally and emerge from an intact seed. In 3 cases (Delonix regia, Parkinsonia aculeata and Schizolobium parahybum), the bruchid developed to a full—sized larva or an adult in the embryo of the seed but was unable to emerge by itself. In 9 species, the ♀ beetles refused to ovipost on the seeds, apparently because they were too small or because they were tomentose. It appeared that larvae failed to penetrate seed coats both because of their hardness and their toxicity. This demonstration that seed coats can be a barrier to a bruchid complicates the interpretation of the toxicity of seed contents and emphasizes the need to analyze seed contents separately from seed coats.