Microplitis croceipes is a solitary larval parasitoid of Helicoverpa/Heliothis species in North America. Laboratory experiments were conducted to determine suitability of the non-natural host, a Japanese strain of Helicoverpa armigera for parasitism by M. croceipes. Females oviposited in the third instar of H. armigera. When the parasitized hosts were reared with artificial diet at 15-30°C with 16L:8D, 67-92% of them produced parasitoid pupae. However, only 9% at 13°C and 53% at 33°C produced parasitoid pupae, and none of those parasitoid pupae developed to adults at these temperatures. Mean time taken from oviposition to adult emergence varied from 14.8 d at 30°C to 53.2 d at 15°C for males and from 15.5 d at 30°C to 60.7 d at 15°C for females. The proportions of females in the emerged adults were 0.45-0.56. Mean lengths of forewings varied from 4.4 mm at 30°C to 4.9 mm at 15°C for males and from 4.3 mm at 30°C to 4.7 mm at 15°C for females. H. armigera was as suitable for parasitism by M. croceipes as H. zea and H. virescens, natural hosts of this parasitoid. The optimal temperature range for development of M. croceipes was 20-28°C.