Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2009
Publication Date: 6/1/2009
Citation: Rull, J., Wharton, R., Feder, J., Guillen, L., Sivinski, J.M., Forbes, A., Aluja, M. 2009. Latitudinal variation in parasitoid guild composition and parasitism rates of North America Hawthorn infesting Rhagoletis. Environmental Entomology. 38:588-599. Interpretive Summary: The apple maggot is a pest that has moved from a native host, hawthorns, to an agricultural commodity, apples, within historic times. Parasitism is much lower in US apples and this may be one reason the host-shift was so advantageous for the fly. Scientists at the USDA-ARS center for Medical, Agricultural and Veterinary Entomology in collaboration with colleagues from the Instituto de Ecologia are trying to determine where the original apple attacking strain developed. If it was Mexico it might be that parasitism in hawthorns is particularly high. This was not the case and efforts will continue to examine other places and evolutionary reasons for the distribution of apple-attacking flies.
Technical Abstract: Rhagoletis pomonella populations in Mexico and the U.S. have diverged by exploiting hosts with different fruiting phenology in environments that differ markedly in temperature and humidity. As a first step to document cascading host associated divergence of the parasitoid guild exploiting Rhagoletis hawthorn infesting flies in their whole geographical range, we report results of a comprehensive five year survey in high altitude (1600- 2500 m.) habitats, over 21 states in México and three sites in the U.S.. In Mexico, collections of infested fruit ranged in distribution from N (e.g., neighboring Texas) to S Mexico (e.g., Chiapas neighboring Guatemala) with a total of eight species of hawthorn sampled. Of 35046 fly pupae, we only obtained 652 adult parasitoids (all Braconidae). Overall (all parasitized samples considered), percent parasitism was 10.85 + 10.76 %. Both flies and some parasitoids entered diapause which could last from 5 to 8 months depending on the population. Parasitoid species found infesting R. pomonella in Mexico were: Aganaspis pelleranoi, Asobara sp., Diachasmimorpha longicaudata, Diachasma mellea, Dorycobracon aerolatus, Opius sp. Utetes anastrephae, and Utetes canaliculatus. Parasitoid species richness in high altitude temperate areas at low latitudes was similar to that of temperate areas at high latitudes, but parasitism rates were much lower. Only U.canaliculatus expressed diapause patterns suited to the different phenologies of genetically differentiated populations of its tephritid host. It is not clear what accounts for differences in parasitism rate, although differences in humidity, timing of host fruit ripening, and length of the tephritid host diapause period may be partly responsible.