HOST-ASSOCIATED FITNESS VARIATION IN A SEED BEETLE (COLEOPTERA, BRUCHIDAE) - EVIDENCE FOR LOCAL ADAPTATION TO A POOR QUALITY HOST

The geographic distributions of many generalist herbivores differ from those of their host plants, such that they experience coarse-grained spatial Variation in natural selection on characters influencing adapt ation to host plants. Thus, populations differing in host use are expe cted to differ in their ability to survive and grow on these host plan ts. We examine host-associated variation in larval performance (surviv orship, development time, and adult body weight) and oviposition prefe rence, within and between two populations of Stator limbatus (Coleopte ra: Bruchidae) that differ in the hosts available to them in nature. I n one population, Acacia greggii (Fabaceae: Mimosoideae) and Cercidium microphyllum (Fabaceae: Caesalpinioideae) are each abundant, while in the second population only C. floridum and C. microphyllum are presen t. In both populations, egg-to-adult survivorship was less than 50% on C. floridum, while survivorship was greater than 90% on A. greggii. M ost of the mortality on C. floridum occurred as larvae were burrowing through the seed coat; very low mortality occurred during penetration of the seed coat of A. greggii. Significant variation was present betw een populations, and among families (within populations), in survivors hip and egg-to-adult development time on C. floridum; beetles restrict ed to Cercidium in nature, without access to C. floridum, survived bet ter and developed faster on C. floridum than beetles that had access t o A, greggii. Large host effects on body size were detected for female offspring: females reared on A. greggii were larger than those reared on C. floridum, whereas male offspring were approximately the same si ze regardless of rearing host. Trade-offs between performance on C. fl oridum and C. floridum were not detected in this experiment. Instead, our data indicate that development time and survivorship on C. floridu m may be largely independent of development time and survivorship on A . greggii. Patterns of oviposition preference corresponded to the obse rved patterns of host suitability: in laboratory preference tests, bee tles with access to A, greggii in nature tended to prefer this host mo re than beetles without access to this host in nature.