none. The range of host instar-age categories accepted by Microplitis croceipes (Cresson), Microplitis demolitor Wilkinson, Cotesia kazak (Telenga), and Hyposoter didymator (Thunberg) was investigated. Heliothis virescens (F.) was the host used. To study host instar-age acceptance, females of each species were exposed in the laboratory to 1st instar larvae, 24 and 48 h old, 2nd instar larvae, 72 and 96 h old, 3rd instar larvae, 120 and 144 h old, 4th instar larvae, 168 and 192 h old, and 5th instar larvae, 216 and 240 h old. A host larva was considered to be accepted by a female if she laid an egg in the larva. The full range of host instar-age acceptance was 1st instar-24 h old to 5th instar-240 h old for M. croceipes , 1st instar-24 h old to 5th instar-216 h old for M. demolitor , 1st instar-24 h old to 4th instar-192 h old for C. kazak , and 1st instar-24 h old to 4th instar-192 h old for H. didymator . Mean development times for male and female progeny and the mean percent mortality were also determined for each parasitoid species for each instar-age category.