Effect of host decoys on the ability of the parasitoids Muscidifurax raptor and Spalangia cameroni to parasitize house fly (Diptera: Muscidae) puparia

Authors: Johnson, Dana; RIZZO, EMILY - University Of Florida; Taylor, Caitlin; Geden, Christopher - Chris

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2017
Publication Date: 7/10/2017
Citation: Johnson, D.M., Rizzo, E., Taylor, C.E., Geden, C.J. 2017. Effect of host decoys on the ability of the parasitoids Muscidifurax raptor and Spalangia cameroni to parasitize house fly (Diptera: Muscidae) puparia. Florida Entomologist. 100:444-448.

Interpretive Summary: House flies cost the US livestock industry an estimated $300 million per year and are important carriers of food-borne diseases. Fly control is becoming increasingly difficult because of insecticide resistance and public concerns about food safety. Parasitic wasps that kill the fly in the pupal stage can be an effective alternative tool for fly management. Farmers can buy the wasps from companies that ship them as young wasps that are still inside fly pupae. The parasitized pupae can then either be scattered over breeding areas or placed in sheltered release stations. Both methods have advantages. One of the concerns about the scatter method is that the hatched wasps might waste too much time examining and rejecting the empty pupal cases from which they emerged and therefore be less effective at finding and killing live fly pupae. In this study, conducted at the USDA’s Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, Florida, two species of wasps were tested to see how easily they could find live fly pupae when they were mixed with empty pupal cases that had already produced wasps (“duds”). One species was unaffected by the presence of dud pupae in their environment and the other species was only slightly affected. These results support the recommendation for using the scatter method when releasing the wasps for fly control.

Technical Abstract: The pteromalid pupal parasitoids Muscidifurax raptor Girault and Sanders and Spalangia cameroni Perkins (Hymenoptera: Pteromalidae) are commonly released on livestock farms for management of house flies (Diptera: Muscidae). To be effective, parasitoids must be able to locate live host puparia in complex environments that may include dead/formerly parasitized hosts as well as non-host physical objects. In this study, both species of parasitoids were examined for their ability to kill and parasitize live house fly puparia either alone or in mixtures with formerly parasitized (dead) hosts or acrylic beads that were similar in size and shape to the puparia. Muscidifurax raptor killed significantly fewer hosts and produced fewer progeny when they were provided with hosts that were mixed with formerly parasitized puparia. Spalangia cameroni was unaffected by the presence of formerly-parasitized puparia for any of the measured variables. When beads were used as a decoy instead of formerly-parasitized puparia, high bead to live host ratios (90% decoys) resulted in significantly lower numbers of hosts killed by M. raptor compared with the other treatments (50% and no decoys). Residual host mortality at the high bead to live host ratio (90% decoys) was lower (31.2%) than in ratios of 50:50 and with no decoys (51.6 and 59.3%, respectively), so that progeny production by M. raptor was unaffected by the presence of beads. Spalangia cameroni killed over twice as many hosts and produced twice as many progeny in the absence of bead decoys than when beads made up 90% of the decoy/host mixture.