Öz The effects of some antibiotics and antifungal agents in different levels and combinations on the survival and development of the hymenopterous endoparasitoid, Pimpla turionellae \\erc investigated by rearing the larvae aseptically on chemically defined synthetic diets. These effects varied with the kinds and levels of the antimicrobial agents in the combinations. The effects of antimicrobial agents tested were mostly exerted during the post-larval developmental stages. Some of the combinations also exerted their effects on the larval survival and development. In general, except a combination of nystatin with methyl p-hydroxybenzoate, the other tested combinations of two antimicrobial agents had negative effects on the post-larval survival of the insect.The diet with 45mg of nystatin and 2.5 mg of methyl p-hydroxybenzoate caused a significant increase in the number of survivors in the post-larval stages and shortened the developmental time for these stages. When added 30 mg of nystatin to the diet with a combination of penicillin and rifampicin (20:2.5 mg) the post-larval survival was significantly increased. The other tested combinations of three antimicrobial agents had no noticeable effects on the insect.