none The reproductive biology of Microplitis brassicae Muesebeck was investigated at five different constant temperatures. This solitary internal parasite oviposits in first and second instars (0-6 days old) of its host Trichoplusia ni (Huebner). Duration of development from egg to adult ranged from 17.7 days at 21.1 degree C to 10.7 days at 32.2 degree C. Adult longevity ranged from 55.5 days at 15.5 degree C to 12.9 days at 32.2 degree C for males, and from 76.4 days at 15.5 degree C to 13.7 days at 32.2 degree C for females. Sexes were significantly different in their longevities only at 15.5 degree C. Total progeny production was significantly greatest at 21.1 degree C, averaging 73.2 progeny per female. Levels of progeny production were near zero at the low (15.5 degree C) and high ends (35.0 degree C) of the temperature range tested. Rearing methods, mating, searching, and ovipositional behaviors are described.