Selection responses and quantitative-genetic analysis of preadult performance on two host plants in the bean weevil,Acanthoscelides obtectus.

The most popular hypothesis that explains host specialization in herbivorous insects assumes the presence of a genetic trade-off in larval performance across host plant species. We examined whether there is a genetic trade-off in preadult performance traits on two hosts in the bean weevil, Acanthoscelides obtectus Say (Coleoptera: Bruchidae). Well-established laboratory populations of A. obtectus were maintained on two plant species, one being the native host (bean) and the other a novel, unsuit- able host (chickpea). After 50 generations of laboratory rearing, preadult survival and development time on each host plant were compared between the two populations. A split-brood design was used to estimate cross-host genetic correlations in the two traits and to compare the populations in their patterns of genetic variation over the two plants. We detected a survival cost paid by A. obtectus on its native host for the increasing adaptation to the novel one, and a significant population x host interaction for survival. The host effect on survival was significant in the bean-adapted population. The additive genetic variances for survival and female development time were only expressed on the novel host, and the half-sib family mean correlations across hosts were zero for both traits in both populations. However, the sire x host interaction for survival was not recorded in either population, whereas the sire x host interaction and non-additive genetic variance for development time evolved during the selection on the novel host. [ABSTRACT FROM AUTHOR]