AbstractDiplolepis ogawaiAbe and Ide sp. nov. (Hymenoptera: Cynipidae) induces galls onRosa hirtula(Regel) Nakai (Rosales: Rosaceae), which is endemic to a restricted area of Honshu, the main island of Japan. The gall is induced mainly on the leaf ofR.hirtulain spring and the mature gall falls to the ground in early summer. The gall-inducing wasp emerges from the gall on the ground in the following spring, suggesting thatD.ogawaiis univoltine. From spring to summer, the braconidSyntomernus flavusSamartsev and Ku and the eulophidAprostocetussp. are parasitic on the larva ofD.ogawaiin the gall, and the adult wasp of both parasitoid species emerges from the gall on the ground in summer. ForS.flavus, this is the first distribution record in Japan and the first host record. SinceR.hirtulais threatened with extinction by succession and deforestation,D.ogawaiand its two parasitoid wasp species are considered to be at risk of coextinction with the threatened rose. In the event that the population size of this rose species is further reduced,D.ogawaiand its parasitoids may ­become extinct prior to the extinction ofR.hirtula. To conserve these three wasp species associated withR.hirtula, protection of remnant vegetation where individuals of this threatened rose species grow is necessary.