After more than 350 years, what native parasitoids attack an introduced gall wasp on an introduced plant?

Abstract Introduced phytophagous insects that use native host plants tend to recruit native parasitoids either from among those attacking native insect hosts closely related to the introduced insect or from among those attacking other insects feeding on the adopted host plant of the introduced herbivore. The introduced North American cynipid gall wasp Liposthenes glechomae Linnaeus 1758 (Hymenoptera: Cynipidae: Aulacideini) is peculiar in that neither the wasp nor its host plant, the ground ivy Glechoma hederacea, has congeners in North America. Consequently, there would appear to be few opportunities for parasite recruitment. We studied the origins of the parasitoid wasp community of L. glechomae in North America by collecting in Iowa and Pennsylvania, dissecting and rearing insects from galls and sequencing larvae and adults. We found 3 parasitoid species. Two of these, Phaenocytus glechomae Förster, 1841 (Hymenoptera: Pteromalidae) and Torymus cingulatus Nees von Esenbeck, 1834 (Hymenoptera: Torymidae), were not new recruits but rather parasitoids of L. glechomae in its native range that have followed their host gall wasp and its host plant to North America. Of the 3 parasitoid species recorded, only 1 is native to North America, Torymus advenus Osten-Sacken, 1870 (Hymenoptera: Torymidae), a generalist that also attacks many different cynipid gall wasps and gall midges associated with a variety of Nearctic plants. After more than 3 centuries in North America, L. glechomae has recruited just 1 new parasitoid in the studied region.