Comparison of the Olfactory Preferences of Four of Filth Fly Pupal Parasitoid Species (Hymenoptera: Pteromalidae) for Hosts in Equine and Bovine Manure

House flies (Musca domestica L.) and stable flies (Stomoxys calcitrans (L.)) (Diptera: Muscidae) are common pests in equine and cattle facilities. Pupal parasitoids, primarily in the genera Spalangia and Muscidifurax (Hymenoptera: Pteromalidae), can be purchased for biological control of these flies. However, little is known about the host-habitat preferences associated with host-seeking by these parasitoids. The preferences of two Spalangia and two Muscidifurax species to odors associated with house fly hosts in equine and bovine manure were investigated in the laboratory using a Y-tube olfactometer. Odor stimuli from manure without developing flies, third-instar house flies in manure, and fly host puparia in manure were evaluated. In choice tests, S. cameroni and S. endius were strongly attracted to odor associated with equine manure against clean air. Although S. cameroni was attracted to all bovine manure-containing treatments against clean air, S. endius was only attracted to the bovine manure with third-instar flies. There were no significant differences between the Spalangia species in odor responses. Neither Muscidifurax species were attracted to equine manure treatments and were only attracted to the bovine manure with puparia over clean air. In manure comparison studies, bovine treatments with developing flies were more attractive than the equivalent equine treatments to both Muscidifurax species The data suggest that coexistence between the competing pteromalid parasitoids might be promoted by different host-seeking behaviors. Additionally, manure preferences may indicate parasitoid suitability for releases on different livestock and equine facilities.