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 a bout the impact of this environmental factor on natural enemies of house fl ies. Five species of parasitoids [Muscidifurax raptor Girault & Sanders, Sp alangia cameroni Perkins, Spalangia endius Walker, Spalangia gemina Boucek, and Dirhinus himalayanus (Masi)] were evaluated for their ability to locat e 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 stron gly to manure containing 45% moisture, with little change in search pattern s caused by host density. The 3 Spalangia spp. showed a strong preference f or manure containing 45-65% moisture, but attacked pupae in wetter manure w hen hosts were in short supply. S. endius showed the strongest preference a mong the Spalangia spp. for dry manure, attacking twice as many hosts in th e 45% moisture treatments as in the 55 or 65% treatments. D. himalayanus wa s 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-spe cies releases in poultry houses that are heterogeneous with respect to mois ture conditions.