D.W. Watson

Seasonal Activity of Entomophthora muscae (Zygomycetes: Entomophthorales) in Musca domestica L (Diptera: Muscidae) with Reference to Temperature and Relative Humidity

Abstract The fungus, Entomophthora muscae (Cohn) Fresenius, commonly infects house flies, Musca domestica L., on feedlots and dairies in southeastern Nebraska. During two fly breeding seasons, disease prevalence increased from

Comparison of sentinel and naturally occurring fly pupae to measure field parasitism by pteromalid parasitoids (Hymenoptera)

Abstract In a series of studies over a 4-year period, the effectiveness of releases of pteromalid wasps for the control of house flies, Musca domestica L., and stable flies, Stomoxys calcitrans (L.), on beef cattle confinements was evaluated using sentinel house fly pupae (artificially reared and placed in the environment) and naturally occurring house fly and stable fly pupae. The two methods were compared using percentage parasitoid emergence and species composition. At confinements where no parasitoid releases occurred, parasitoid emergence was significantly higher from naturally occurring hosts. Muscidifurax zaraptor Kogan and Legner comprised 97 and 76% of the parasitoids recovered from sentinel and naturally occurring hosts, respectively. Spalangia spp. made up 16% of the parasitoids from naturally occurring hosts. Few Spalangia spp. were recovered from sentinel hosts. Similar results were obtained from locations where M. zaraptor was released except that M. zaraptor comprised a greater proportion of the parasitoids recovered by both methods. At locations where Spalangia cameroni Perkins was released, 76% of the parasitoids recovered from sentinel hosts were M. zaraptor, and 21% were S. cameroni, compared with 62% M. zaraptor and 34% S. cameroni from naturally occurring hosts. At locations where Pachycrepoideus vindemiae (Rondani) was released, this species was recovered significantly more often from sentinel hosts. Naturally occurring pupal method appears to be more reliable and sensitive to the entire parasitoid species complex. However, because of the difficulty in obtaining adequate samples, it is recommended that both methods be employed.

Parasitoid-induced mortality of house fly pupae by pteromalid wasps in the laboratory

Abstract House fly, Musca domestica L., pupae were exposed to six species of pteromalid parasitoids, Muscidifurax zaraptor Kogan and Legner, M. raptor Girault and Sanders, M. raptorellus Kogan and Legner, Pachycrepoideus vindemiae (Rondani), Spalangia nigroaenea Curtis, and Urolepis rufipes Ashmead. Exposures were made for 48 h at six parasitoid-to-host ratios to measure the effect of parasitoid density on parasitoid-induced mortality (PIM) of hosts (excluding mortality as measured by parasitoid emergence). PIM was evident at all parasitoid-to-host ratios for all six species. Fly eclosion declined with a corresponding increase in the parasitoid-to-host ratio; the reverse was generally true for PIM. Parasitoid emergence increased initially with a corresponding increase in the parasitoid-to-host ratio to a point (depending on the parasitoid species), but then declined. The three Muscidifurax spp. and P. vindemiae exhibited similar behavior and generally avoided previously stung hosts until ovipositional restraints broke down at the higher parasitoid-to-host ratios. S. nigroaenea and U. rufipes exhibited little ovipositional restraint, resulting in a high proportion of PIM of hosts. Understanding factors that influence PIM will provide better evaluations of field releases of parasitoids to control flies and will aid in the development of the most economic procedures for large scale rearing of pteromalid parasitoids.

Evaluation of Muscidifurax zaraptor and Pachycrepoideus vindemiae (Hymenoptera: Pteromalidae) for controlling flies associated with confined beef cattle

Abstract Releases of Muscidifurax zaraptor Kogan and Legner and Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae) were made at four beef cattle feedlots in eastern Nebraska. The ability of the parasites to parasitize house fly (Musca domestica L.) and stable fly [Stomoxys calcitrans (L.)] pupae under ambient environmental conditions was measured. The two species were released seven times at 2-week intervals from a central location within each of the four feedlots. Both species were recovered significantly more often from sentinel pupae placed around the perimeter of each feedlot than from sentinel pupae at untreated feedlots. Mean mortality of sentinel pupae for the four release feedlots ranged from 28 to 42% compared with 4.8% for two untreated feedlots. Parasites recovered from sentinel pupae comprised 87% M. zaraptor and 12% P. vindemiae. Correlations between the percentage mortality of sentinel pupae and the number of parasites released were poor. However, when the interaction of weekly mean air temperature was considered, a significant correlation between reduction of sentinel pupae and the number of parasites released was evident. Differences in parasitism between release and control sites were not as apparent when parasite emergence from naturally occurring house fly and stable fly puparia was determined. The indigenous M. zaraptor was clearly superior to the introduced P. vindemiae and readily parasitized house fly pupae placed around the perimeter of the release feedlots. The results also suggested that periods of mean weekly temperature exceeding 27°C appeared to adversely affect both parasite species.