Abai, MR

6th International Congress of DipterologyHost race formation by Eurosta solidaginis on subspecies ofSolidago altissimaCraig, T.P. (1) & J.K. Itami (1)(1) Department of Biology, University of Minnesota Duluth, Duluth Minnesota 55812-3004, USAEurosta solidaginis, a gall-inducing fly (Diptera: Tephritidae) showsevidence of having formed host races on two subspecies Solidagoaltissima: S. altissima altissima which is found in the forest biome, and S.altissima gilvocanescens which is found in the prairie biome. The E.solidaginis populations in the prairie and the forest show significantdifferences in allozyme frequencies indicating partial reproductiveisolation between the populations. Gall size and shape of the two E.solidaginis populations in the two biomes also differ significantly betweenprairie and forest populations. Prairie and forest flies had different wingpatterns with a cline of wing patterns indicating that there is a hybrid zone.In a common garden experiment both the prairie and forest E. solidaginispopulations had higher rates of gall induction and survival on thesubspecies from their biome. The forest fly population had a strongpreference for ovipositing on plants from the forest, while the prairie flypopulation did not show a preference between host populations. Bothpopulations showed an oviposition preference for tall host plants, and theforest S. a. altissima was significantly taller than the prairie S. a.gilvocanescens in both the field and in the common garden experiment,and this influenced oviposition preference. We measured gall diameter inthe field and in the common garden experiment. We found that galldiameter was significantly influenced by the fly origin and the environment(field versus common garden), but that it was not influenced by the plantorigin. These results are the first evidence of host race formation on hostplants that are differentiated below the species level.Key Words: oviposition preference, offspring performance, host race,speciation, gall51