Dispersal of the Filth Fly Parasitoid Muscidifurax raptorellus (Hymenoptera: Pteromalidae) Following Mass Releases in Cattle Confinements

Pupae of house fly, Musca domestica L. (Diptera: Muscidae), reared in the laboratory were used to assess the movement of Muscidifurax raptorellus Kogan & Legner (Hymenoptera: Pteromalidae) following mass releases of this filth fly parasitoid in cattle confinements. Parasitism of sentinel pupae was 34%, averaged for three mass releases (≈220,000 individuals/release) at each of two sites. Parasitism declined only slightly with the distance (1 to 100 cm) of pupae from the point of parasitoid release (for data combined from all releases, P < 0.001, r2 = 0.032). Wind direction had no consistent effect on parasitism for six releases (P > 0.05). Twenty-nine specimens of M. raptorellus were recovered in 1998, following release of more than 1.3 million individuals in previous years. Because the winter of 1997–1998 was unusually warm, further studies are required to determine whether the parasitoid can survive winters more typical of southern Alberta. These results suggest that (1) mass releases of M. raptorellus can be used to help manage populations of stable fly and house fly in cattle confinements, (2) mass releases at intervals of 200 m should achieve fairly uniform coverage of the confinement facility with parasitoids, and (3) mass releases will be required each year. Eight additional species of parasitoids (Hymenoptera) were recovered from pupae during the study. Each of these species previously has been reported from house fly pupae in Alberta, with the exception of Eupelmus (Macroneura) vesicularis (Retzius) (Eupelmidae).