Host location by Spalangia cameroni (Hymenoptera: Pteromalidae) in equine associated substrates

House flies, (Musca domestica L.) and stable flies (Stomoxys calcitrans L.) are common pests on equine facilities. Biological control of these flies with pupal parasitoids has become increasingly popular with horse owners but has not been evaluated on equine facilities. Little is known of the substrate preferences of filth fly parasitoids on equine facilities, but the success of release programs may be affected by microhabitat preferences. Spalangia cameroni Perkins was evaluated for location preferences for parasitization of house fly and stable fly puparia in six substrates commonly found on equine farms in Florida. Substrates were evaluated at 20:1 and 5:1 H:P ratios and during the experiment parasitoids had access to all substrates simultaneously. No differences were observed between filth fly host species in any of the measured parameters: total host mortality, parasitoid progeny production and residual host mortality. Significant effects of H:P ratio on host mortality and residual mortality were found but not on progeny production. While there were significantly more hosts killed in the aged shavings than the fresh shavings at the 20:1 ratio, no differences were observed at the 5:1 ratio. Additionally, no differences were found in progeny production across substrates at the 20:1 ratio, but higher reproductive success was observed in several substrates at the 5:1 ratio. These results demonstrate that S. cameroni had substrate preferences but that these preferences were absent with reduced host density. This parasitoid species appears to be effective at parasitizing hosts in the common equine substrates of Florida.

Highlights► Substrate influenced host seeking of Spalangia cameroni at low host densities. ► With fewer hosts, Spalangia cameroni had greater flexibility for host seeking in substrates. ► Species of host did not have any effect on host seeking of Spalangia cameroni. ► Increased host:parasitoid ratio did not increase parasitoid progeny production. ► Spalangia cameroni appears to be a suitable candidate for release.