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The hemlock woolly adelgid, Adelges tsugae, is causing widespread mortality of eastern hemlock, Tsuga canadensis, in the eastern United States. In the West, A. tsugae causes negligible damage to western hemlock, Tsuga heterophylla. Host tolerance traits and presence of endemic predators may be contributing to the relative tolerance of western hemlock to A. tsugae. Field surveys of the predator community associated with A. tsugae infestations on 116 T. heterophylla at 16 locations in Oregon and Washington were conducted every four to six weeks from March 2005 through November 2006. Predators collected from A. tsugae infested T. heterophylla represent 55 species in 14 families, listed in order of abundance: Derodontidae, Chamaemyiidae, Hemerobiidae, Coccinellidae, Cantharidae, Reduviidae, Miridae, Syrphidae, Chrysopidae, Coniopterygidae, Staphylinidae, Anthocoridae, Nabidae, and Raphidiidae. Laricobius nigrinus (Derodontidae), Leucopis argenticollis, and Leucopis atrifacies (Chamaemyiidae) are the most abundant predators; together comprising 59% of predator specimens recovered. The abundance of derodontid larvae, L. nigrinus adults, chamaemyiid larvae, and L. argenticollis adults was found to be positively correlated to A. tsugae density. The remaining 52 species represent a diverse complex of predators potentially attacking A. tsugae. However, many are known to feed on non-adelgid prey. Predators were most abundant when the two generations of A. tsugae eggs were present. The phenology of immature and adult predators suggests temporal partitioning of prey across all seasons. Fifteen predator species were either reared from larvae to adult on a diet of A. tsugae in the laboratory or were observed feeding on A. tsugae. L. argenticollis and L. atrifacies were reared on A. tsugae in the laboratory and host records show them to feed exclusively on Adelgidae. Both species should be investigated as candidates for A. tsugae biological control in eastern North America. |
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