Rhinocyllus  Rhinocyllus is a small genus of true weevil, with about 4 species described. This genus's host plant are thistles in the subtribe Carduinae. The genus's sister group is "Bangasternus". The genus's most infamous species is "R. conicus" which is a controversial agent of biological pest control which has been used against noxious thistles in the genera "Carduus", "Cirsium", "Onopordum", and "Silybum".