Host specificity of Mogulones cruciger (Coleoptera: Curculionidae), a biocontrol agent for houndstongue (Cynoglossum officinale), with emphasis on testing of native North American Boraginaceae.
Recent concerns over the safety of native North American plant species in the family Boraginaceae, especially those of endangered status in the USA, prompted additional host specificity testing of the European root weevil Mogulones cruciger [Ceutorhynchus cruciger], a proposed agent for the biocontrol of houndstongue in the USA. M. cruciger can complete full development on species within closely-related genera in the Boraginaceae, but prefers houndstongue as a host. Of the 22 species of native North American Boraginaceae that were tested in this study, nine species from four genera within the tribe Eritrichieae (Cryptantha, Hackelia, Mertensia and Lappula) clearly supported development of M. cruciger. However, generally these non-target species experienced less attack by M. cruciger relative to houndstongue. There were differences in the incidence and degree of attack depending on the test type, which included the use of potted test plants in laboratory no-choice and open-field choice situations. The least non-target attack occurred on rangeland in British Columbia, Canada, where potted test plants were introduced into sites where the insect had been previously released on houndstongue. These results suggest that M. cruciger has a narrow ecological host range. Special emphasis was placed on testing species of Cryptantha because C. crassipes is listed as endangered in the USA. Six of 12 Cryptantha species tested supported full development, but generally, the incidence and intensity of attack were less for these species relative to houndstongue. There was no, or incomplete development, on tested species of Plagiobothrys, a genus that contains two species listed as endangered in the USA.