Biology and host specificity of Rhinusa pilosa,a recommended biological control agent of Linaria vulgaris

Linaria vulgaris Mill. (Plantaginaceae), common or yellow toadflax, is a Eurasian short-lived perennial forb invasive throughout temperate North America. Rhinusa pilosa (Gyllenhal) (Coleoptera, Curculionidae) is a univoltine shoot-galling weevil found exclusively on L. vulgaris in Europe. Under no-choice test conditions, 13 non-native Linaria species exposed to R. pilosa were accepted for oviposition and most were found to be suitable, to varying degrees, for gall and larval development. Adult feeding and survival was minimal on native North American species in the plant tribe Antirrhineae which includes the target plant. In no-choice tests with 63 native North American species and 24 other non-target species outside Linaria, oviposition was limited to four native North American species. Only three larvae developed to the adult stage on Sairocarpus virga (A. Gray) D.A. Sutton, with no negative impact on plant growth. Risks to native flora from the release of R. pilosa are therefore expected to be minimal. The Technical Advisory Group for the Biological Control of Weeds (TAG—BCW) has recommended release of R. pilosa in September 2013.