Filth Flies Feel the Heat

Commercial insectaries that produce wasps as biocontrol agents will benefit from new Agricultural Research Service (ARS) findings showing that killing fly pupae—the food source for the wasp larvae—with heat shock is an affordable alternative to irradiation. The heat shock alternative will help insectaries meet fluctuating demand for two parasitic wasps used to control filth flies.

House flies and stable flies are nuisances on livestock and poultry farms, and they transport disease-causing organisms. Parasitic wasps released as biocontrols can reduce the need for insecticides on livestock and poultry farms.

Wasp species such as Muscidifurax raptor and Spalangia cameroni lay a single egg inside a fly puparium before it hatches, and the larva feeds on the fly pupa before emerging as an adult. But it takes one week to produce fly pupae for the parasitoids, and these live pupae only have a shelf life of two to three days. So insectaries turned to ARS for help.

Entomologist Christopher J. Geden of the ARS Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, Fla., studied fly pupae killed with gamma irradiation, cold and heat shock for their ability to produce parasitoids.

Researchers have reared parasitoids with irradiated pupae for years, but it's not practical for commercial insectaries. Previous results from freeze-killing pupae have been mixed. Heat shock killing in an oven had never been tried before.

The number of wasp progeny, male or female, emerging from pupae killed by heat shock or gamma irradiation was not significantly different from those produced on live hosts.

Geden found heat-killed, irradiated and freeze-killed pupae stored in refrigerated plastic bags remain as effective for production of M. raptor as live pupae for as long as four months.

Production of S. cameroni on heat-killed and irradiated pupae was equal to parasitoid production on live pupae for up to two months of storage. After that, production declined to 63 percent of live pupae. Production of S. cameroni on freeze-killed pupae was about 75 percent of production using live pupae for eight weeks of storage but declined rapidly afterward.

ARS is the U.S. Department of Agriculture's chief scientific research agency.