Consequences of inbreeding for the cowpea seed beetle, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Abstract

Inbreeding is said to reduce vigour and fitness. It may also determine how a population responds to selection. Local populations of Callosobruchus maculatus, the cowpea seed beetle, are established annually from small numbers of founders and the species has been distributed to many 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 ancestral stock in similar directions with respect of some variables such as developmental speed, but haphazardly in respect of other parameters such as male weight. The respective roles of drift and of selection as effective evolutionary forces in inbred lines are discussed in the light of these results. It is argued that some intraspecific differences in C. maculatus may be explained as a product of periodic inbreeding, but that the process does not impair the ability to adapt to local conditions so contributing to the status of the species as a pest of international importance.