none Laboratory studies were conducted to ascertain some aspects of the biology of Microplitis mediator Hal. Out of 4 lepidopterous hosts tested, oviposition was attempted by M. mediator in two of them, although only Mamestra brassicae L. was suitable host for parasitoid development, which was observed to be a solitary larval endoparasitoid. When left by parasitoid, the host larvae were in the third, fourth or fifth instars. They did not feed more and continued to live for a limited period of time. Females of wasp exhibited arrhenotokous parthenogenecity. Parasitoid development time from egg to adult emergence averaged from 29.1 days at 19 degree C to 15 days at 26 degree C. Longevity of adults ranged from 32.4 days at 17 degree C to 10.2 days at 23.5 degree C.