Colonization of marginal host plants by Callosobruchus seed beetles (Coleoptera: Chrysomelidae): effects of geographic source and genetic admixture

The ability to adapt to a novel host plant may vary among insect populations with different genetic histories, and colonization of a marginal host may be facilitated by genetic admixture of disparate populations. We assembled populations of the seed beetle, Callosobruchus maculatus, from four continents, and compared their ability to infest two hosts, lentil and pea. We also formed two cross-continent hybrids (Africa x N.A and Africa x S.A.). In pre-selection assays, survival was only ~3% in lentil and ~40% in pea. For three populations per line, colonization success on lentil was measured as cumulative exit holes after 75-175 days. On pea, we estimated the change in larval survival after five generations of selection. Females in all lines laid few eggs on lentil, and survival of F1 larvae was uniformly <5%. Subsequently, however, the lines diverged considerably in population growth. Performance on lentil was highest in the Africa x N.A. hybrid, which produced far more adults (mean &...