Tachinaephagus zealandicus Ashmead is a gregarious endoparasitoid that attacks third instars of muscoid flies in the Southern Hemisphere. The purpose of the current study was to evaluate the influence of six constant temperatures (16, 18, 20, 22, 25, and 27°C) on development time, the influence of emergence order on longevity, and the effects of temperature and food treatment on longevity. Emergence success was greatest at 22°C for both males and females; significantly fewer (24.1–30.4%) parasitoids emerged at 16 and 25°C compared with 22°C. Development time ranged from 24.0 to 56.9 d for both sexes. No emergence was observed at 27°C. Early-emerging parasitoids had greater longevity than parasitoids that emerged later from the same cohorts. The longevity of females given honey and water decreased with increasing temperature, and those reared at 16°C lived about three times longer than those kept at 27°C. Females given honey and water had similar longevities at 16–20°C, and females that were given only water lived for only 4.8–7.6 d at all temperatures. Females lived significantly longer overall than males at all temperatures except 16°C, but differences due to sex were small compared with the effects of temperature and nutrition. Further investigations will be necessary to determine the climatic zones in which T. zealandicus is most likely to be an effective biological control agent of muscoid flies.