Effect of Habitat Depth on Host Location by Five Species of Parasitoids (Hymenoptera: Pteromalidae, Chalcididae) of House Flies (Diptera: Muscidae) in Three Types of Substrates

Four species of pteromalid parasitoids [Muscidifurax raptor Girault & Sanders, Spalangia cameroniPerkins, Spalangia endiusWalker, Spalangia geminaBoucek, and the chalcididDirhinus himalayanus (Masi)] were evaluated for their ability to locate house ßy pupae at various depths in poultry manure (41% moisture), ßy rearing medium (43% moisture), and sandy soil (4% moisture) from a dairy farm. Searching activity in manure was largely conÞned to the surface (M. raptor, D. himalayanus, and S. gemina) or to depths of up to 2 cm below the surface (S. endius, S. cameroni). S. cameroniwas themost effective species at locatingburiedpupae inmanure.All of the species searched over a wider range of habitat depths in ßy rearing medium, although M. raptor and S. gemina tended to concentrate their searching activity relatively close to the surface of the substrate. Host attacks by these species at 6 cm were 30Ð40% lower than on the surface of the medium. S. endius searched uniformly at all depths in rearing medium and S. cameroni had highest rates of host attacks 1Ð2 cm below the surface of this substrate. The parasitoids displayed considerable Þdelity to their search patterns regardless of whether or not they were given a choice of habitat depths in which they could Þnd pupae. None of the parasitoids were effective at attacking ßy pupae that were buried in sandy soil at any depth. The results suggest that ßy larvae that pupate in the sandy soils typical of FloridaÕs coastal plains are relatively impervious to attack by pupal parasitoids.