Host location by house fly (Diptera: Muscidae) parasitoids in poultry manure at different moisture levels and host densities

Manure moisture varies widely under field conditions, but little is known about the impact of this environmental factor on natural enemies of house flies. Five species of parasitoids [Muscidifurax raptor Girault & Sanders, Spalangia cameroni Perkins, Spalangia endius Walker, Spalangia gemina Boucek, and Dirhinus himalayanus (Masi)] were evaluated for their ability to locate house fly, Musca domestica L., pupae in manure containing 45, 55, 65, 75, or 85% moisture at low (2.5:1) and high (50:1) host:parasitoid ratios. M. raptor preferred manure with 75% or less moisture, and responded most strongly to manure containing 45% moisture, with little change in search patterns caused by host density. The 3 Spalangia spp. showed a strong preference for manure containing 45-65% moisture, but attacked pupae in wetter manure when hosts were in short supply. S. endius showed the strongest preference among the Spalangia spp. for dry manure, attacking twice as many hosts in the 45% moisture treatments as in the 55 or 65% treatments. D. himalayanus was similar to M. raptor and preferred dry manure, although this species had low overall rates of host attacks and reproduction compared with the other species. The results suggest that releases of combinations of species with different manure moisture preferences may be more effective than single-species releases in poultry houses that are heterogeneous with respect to moisture conditions.