Hymenopterous parasitoids of filth fly (Diptera : Muscidae) pupae in cattle feedlots

Results of a 2-year survey in Alberta, Canada, identified a parasitoid faun a of filth flies distinct from that generally reported for cattle confineme nts in the United States. Twenty-two feedlots were surveyed using freeze-ki lled sentinel house fly pupae. Parasitism averaged 0.25%. Ten species of hy menopterous parasitoids were recovered. As a percentage of the total number of pupae parasitized, these species were Muscidifurax raptor Girault & Sau nders (37.4%), Trichomalopsis sarcophagae Gahan (23.9%), Urolepis rufipes ( Ashmead) (18.5%), Muscidifurax zaraptor Kogan & Legner (6.9%), Nasonia vitr ipennis Walker (6.5%), Trichomalopsis sp. (3.7%) (Pteromalidae), Phygadeuon sp. (2.9%) (Ichneumonidae), Dibrachys cavus (Walker) (0.1%) (Pteromalidae) , Synacra sp. (0.1%) (Diapriidae), and an unidentified Braconidae (0.1%). N o differences were detected among natural regions of the province. Three ca tegories of seasonal activity are identified which expand on previous group ings of species by their geographic distributions. The abundance of T. sarc ophagae and rarity of species of Spalangia Latreille, 1805 are in marked co ntrast to results of surveys conducted in the United States. This differenc e suggests that species used to manage populations of pestiferous flies ass ociated with livestock in the United States could be inappropriate for use in Canada.