A key is provided to twenty-four western Palaearctic species of Robineau-Desvoidy. The hosts of twenty-three species which attack Asteraceae are listed, including those being used or investigated as possible weed biocontrol agents. The species are divided into four species groups and the differing host relationships and types of galls induced by these groups are discussed. sp.n. and ssp. ssp.n., associated with spp. and spp. respectively, are described. (Hering) and (Rohdendorf) are both treated as subspecies of (Meigen). is given full specific status and is removed from synonymy. The following new synonymies are made (junior synonyms in parentheses): (Hering) (= Hering); (Linnaeus) (= Robineau-Desvoidy, lectotype designated); (Hering) (= Hering); (Frauenfeld) (= Hering); Macquart (= Rondani, Loew); (Linnaeus) (= Hering, ); (Fabricius) (= Hering, Rondani); (Loew) (= Hering, Loew, Hendel). The possibility that is a species complex is discussed; it is also suggested that and represent the morphological extremes of a complex. The misuse of the name Fabricius in the genus Blot is noted.
