Acquisition of a native hostplant by an introduced oligophagous herbivore

Introduced from Europe, Depressaria pastinacella (Lepidoptera: Oecophoridae), the parsnip webworm, is found throughout E North America not only on the introduced European hostplant Pastinaca sativa (wild parsnip) but also on the native confamilial host plant Heracleum lanatum (cowparsnip). Full-sib families of webworms founded by parents from both hostplants were raised on diets containing fruits of either parsnip or cowparsnip. Identity of the sire in each cross accounted for a significant amount of variance in pupal weight of progeny, indicating the presence of additive genetic variance for this trait. Overall survival is highest for invididuals on diets containing parsnip fruits; mortality of female offspring of adults collected from H. lanatum was markedly higher than mortality of male caterpillars from either host population. This sexual dimorphism in survivorship resulted in sex ratios as high as 3.4:1 in treatments consisting of offspring of H. lanatum adults on diets containing H. lanatum. Preference tests failed to demonstrate any preference for H. lanatum fruits; larvae from one locality exhibited a significant preference for wild parsnip. Larvae fed fruits of cowparsnip exhibited reduced consumption rates and growth rates compared with larvae fed fruits of wild parsnip. -from Authors