Non-target effects of biocontrol agents at the individual plant and population level have put the practice of weed biocontrol under scrutiny. Divergence in environmental safety assessment policies between Canada and the U.S. exist, due in part, to the generally greater diversity of non-target species in the U.S. In 1997, the root-mining weevil Mogulones cruciger (Hbst.) was released in Canada to control houndstongue (Cynoglossum officinale L.). Permission for field release in the U.S. has not been granted due to concerns of the U.S. Fish and Wildlife Service regarding potential non-target effects of M. cruciger on rare and endangered Boraginaceae. To assess the risk associated with the release of the weevil in the U.S., we tested whether eight rare or federally-listed endangered species could support weevil development. All species tested were accepted in choice oviposition tests and five species supported full development of M. cruciger. Monitoring co-occurring confamilial Boraginaceae species at six M. cruciger release sites in Alberta and British Columbia over a two-year period showed that all four co-occurring species were attacked by the weevil; although, to a lesser degree than houndstongue. Our data suggests that the release of M. cruciger in the U.S. may pose risks to native Boraginaceae including rare and endangered species.