Five species of house fly pupal parasitoids,Nasonia vitripennisWalker,Muscidifurax raptorGirault and Sanders,Pachycrepoideus vindemiae(Rondani),Spalangiasp., andApanteles carpatus(Say), were recovered from house fly pupae exposed in controlled-environment, caged-layer poultry facilities during a 17-mo New York statewide survey. Overall, rates of parasitism were low, ranging from 0.2% in early spring to 14.0% in the fall. The number of fly pupae attacked byN. vitripenniswas significantly higher than those killed by the other parasitoid species. Of all parasitized pupae collected in 1981, 76.9% were killed byN. vitripennis. In 1982,N. vitripenniswas responsible for killing nearly 94.8% of all parasitized pupae.N. vitripenniswas also the most abundant parasitoid, accounting for 95.5 and 99.2% of all parasitoids emerging from sentinel pupae during 1981 and 1982, respectively. In addition,N. vitripenniswas the only parasitoid species observed to actively parasitize fly pupae in these facilities during cold winter months when temperatures in the first-floor manure pits ranged from 12 to 16°C. All the other parasitoid species generally were active only during warm summer months.