Influence of Cowpea Pod Maturity on the Oviposition Choices and Larval Survival of a Bruchid Beetle Callosobruchus maculatus

Abstract

The \u27active\u27 or dispersing morph of Callosobruchus maculatus, a pest of stored cowpeas, is presumed to infest cowpea plants in the field prior to harvest. In oviposition choice tests, both normal and active females preferred pods that were full-size but still green over younger, smaller pods or older, mature pods. Exposed seeds were usually preferred over intact pods of all stages, although females laid more eggs on green pods than on the rough-coated seeds of one cowpea variety. Egg-to-adult survivorship was highest for eggs laid directly on seeds. On both green and mature pods high mortality occurred because newly hatched larvae failed to penetrate a seed after they drilled through the pod wall. However, since 20–50% of eggs laid on green pods do develop into adults, cowpea plants are susceptible to C. maculatus well before pods dehisce to expose the seeds. The oviposition preferences of C. maculatus may be strongly influenced by the surface texture of potential oviposition sites