Evidence of a novel oviposition preference in Oecanthus forbesi

William Licht and Timothy P. Craig. Department of Biology, University of Minnesota Duluth, Duluth MN.

Natural selection theory predicts that oviposition preferences will evolve for resources where offspring performance is highest. We studied the oviposition behavior of Oecanthus forbesi, a tree cricket which oviposits on goldenrod plants, but which does not feed on this plant. A high proportion of cricket eggs collected from the field were found in galls induced by the tephritid fly Eurosta solidaginis with only a small number of eggs found in ungalled stem tissue. We also found large geographic variation in cricket population densities. We reared crickets from these galls and measured oviposition in choice experiment enclosures to determine preferences for host plants of different origins, and for host plant tissues. Crickets were mated and then placed in cages with one galled stem and ungalled stem from each of two forest and one prairie sites. O. forbesi preferred gall tissue over ungalled tissue, and galls from the forest biome over those from the prairie biome. The crickets also demonstrated a significant oviposition preference for gall tissue on forest plants from their native site as measured by the number of eggs oviposited per square centimeter. They preferred galls from their local forest site over those from a foreign forest site. These preferences are significant because they provide evidence of a previously undescribed speciation event resulting from shifts in the plant tissues and plants used for oviposition. We are experimentally testing the hypothesis that these oviposition preferences and geographic distribution have evolved in response to natural enemies and climate.