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

Abstract

Four species of pteromalid parasitoids [Muscidifurax raptor Girault & Sanders, Spalangia cameroni Perkins, Spalangia endius Walker, Spalangia gemina Boucek, and the chalcidid Dirhinus himalayanus (Masi)] were evaluated for their ability to locate house fly pupae at various depths in poultry manure (41% moisture), fly rearing medium (43% moisture), and sandy soil (4% moisture) from a dairy farm. Searching activity in manure was largely confined 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. cameroni was the most effective species at locating buried pupae in manure. All of the species searched over a wider range of habitat depths in fly 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 30–40% 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 1–2 cm below the surface of this substrate. The parasitoids displayed considerable fidelity to their search patterns regardless of whether or not they were given a choice of habitat depths in which they could find pupae. None of the parasitoids were effective at attacking fly pupae that were buried in sandy soil at any depth. The results suggest that fly larvae that pupate in the sandy soils typical of Florida’s coastal plains are relatively impervious to attack by pupal parasitoids.