The Alloxystinae (Hymenoptera, Insecta) are a major group of aphid hype parasitoids of potential economic importance in restricting the efficiency of the primary natural enemies of aphids. The taxonomy and systematics of these insects are very poorly understood, and little is known about their host range 2nd ecology. The project will study the twelve species of alloxystines found in a well- characterized aphid-hyperparasitoid community in southern England. Species boundaries will be established by a joint behavioural, morphological and molecular programme. The information obtained will be used to design experiments to test the theory of apparent competition between primary parasitoids, mediated by hyperparasitoids.