The solitary pupal parasiteUrolepis rufipes(Ashmead), a recent isolate from house fly and stable fly puparia in eastern Nebraska, was studied to evaluate its potential as a biological control agent for these fly species. Parasitism was highest at 25°C for two age classes of host pupae. Parasite-induced mortality attributed to host stinging, excluding emerged parasites, increased with temperature, and generally was significantly higher than parasitism. The number of emerging male to female parasites was about equal and males generally began emerging 1 d before females. Development was more rapid than for most other pteromalid parasites of filth flies requiring 10–15 d for first male emergence at 25°C. Apparent diapause was evident with this species and was activated by the temperature at which the developing progeny were subjected.