In novel habitats, exotic herbivorous insects often colonize to coadapted exotic plants from the same native range. To examine the possibility of local adaptation of exotic herbivores, we investigated host specificity of two exotic herbivores: a specialist aphid and a generalist lace bug on an introduced tall goldenrod, Solidago altissima, in Japan.

We hypothesized that the specialist aphid can locally adapt to resistant traits of tall goldenrods, but the generalist lace bug can not adapt to local differences in resistant traits. To test this hypothesis, we conducted a reciprocal inoculation using these exotic herbivores and tall goldenrods from two sites. There was no significant difference in performance of lace bugs on plants from both sites, supporting our hypothesis. On the other hand, aphid inoculation partly supported our hypothesis, although the aphid performance was not the highest on plants from its same sites. Not only plant traits but also other factors, such as predators, parasitoids, and abiotic environments may be important for local adaptation of the aphid.