Drosophila ambigua; Drosophila subobscura; HYMENOPTERAN-PARASITES; Asobara tabida; Host immunity related to successful invasion; DISPERSAL-; NEARCTIC-REGION; West; Successful invasion, possible influencing factor Asobara tabida; DIPTERAN-HOSTS; Drosophila ambigua & D. subobscura; Host immunity related to successful invasion; NEARCTIC-REGION; West; Immunity related to successful invasion. The palearctic Drosophila subobscura Collin and D. ambigua Pomini recently invaded western North America. One possible explanation for their success is that they have a competitive edge over the native species by being immune to local parasitoids. The braconid Asobara tabida Nees, the dominant parasitoid of larvae of the obscura-group in western North America, is used to test this hypothesis. Survival of the parasitoid is as high in D. subobscura and D. ambigua as in two native species, D. pseudoobscura Frolova and D. athabasca Sturtevant & Dobzhansky. Neither of the four species can substantially survive a parasitoid attack. Parasitoids emerging from the palearctic species do not differ in body mass and development time from parasitoids emerging from the nearctic species. It is concluded that the success of the two palearctic Drosophila species in North America is not caused by immunity to local parasitoids. none