Variation in the Suitability of Host Tree Species for Geographically Discrete Populations of Forest Tent Caterpillar

The forest tent caterpillar,Malacosoma disstriaHübner (Lepidoptera: Lasiocampidae), is distributed throughout North American hardwood forests. Although considered polyphagous, regional populations tend to use only a few host species for oviposition, suggesting that M. disstria is more oligophagous than commonly thought. We tested this premise using larvae from Manitoba, Canada; Michigan; and Louisiana in a factorial, reciprocal transplant experiment. Pupal mass, development time, and survivalwere recorded for eachpopulation after rearing larvae inLouisiana on three primary hosts used by southern populations (water tupelo,Nyssa aquaticaL.; sweetgum, Liquidambar styracifluaL.; andwater oak,Quercus nigraL.) and inMichigan on three northern host trees (red oak, Quercus rubra L.; trembling aspen, Populus tremuloides Michaux; and sugar maple, Acer saccharum Marshall). Manitoba, Canada andMichigan populations had the highest pupal mass, best survival, and most rapid development on trembling aspen and red oak, both northern species. Louisiana larvae attained the highest pupal mass on water tupelo, a primary host across the Gulf States. Northern populations grew poorly on water tupelo, whereas Louisiana caterpillars had the smallest pupal mass and poorest survival on sugar maple. Both red and water oaks were acceptable hosts for all three populations. Our results indicate that M. disstria is actually a composite of regionally adapted populations rather than an extreme generalist. It is unclear, however, what mechanisms might reduce gene ßow, allowing such specialization to evolve and persist. We suggest that varying phenology in adult ßight times among populations feeding on different hosts could provide at least a partially isolating mechanism, allowing for the evolution of host adaptation.