CONSEQUENCES OF INBREEDING FOR THE COWPEA SEED BEETLE, CALLOSOBRUCHUS-MACULATUS (F)(COLEOPTERA, BRUCHIDAE)

Inbreeding is said to reduce vigour and fitness. It may also determine how a population responds to selection. Local populations of Callosob ruchus maculatus, the cowpea seed beetle, are established annually fro m small numbers of founders and the species has been distributed to ma ny parts of the world where isolated populations may have been founded by very small numbers of individuals. After more than 20 generations of inbreeding, inbred lines have been shown to diverge from a common a ncestral stock in similar directions with respect of some variables su ch as developmental speed, but haphazardly in respect of other paramet ers such as male weight. The respective roles of drift and of selectio n as effective evolutionary forces in inbred lines are discussed in th e light of these results. It is argued that some intraspecific differe nces in C. maculatus may be explained as a product of periodic inbreed ing, but that the process does not impair the ability to adapt to loca l conditions so contributing to the status of the species as a pest of international importance.