Predators Associated with the Hemlock Woolly Adelgid (Hemiptera: Adelgidae) in the Pacific Northwest

Abstract

The hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is causing widespread mortality of eastern hemlock, Tsuga canadensis L. Carrière, in the eastern United States. In western North America, feeding by A. tsugae results in negligible damage to western hemlock, Tsuga heterophylla (Raf.) Sargent. Host tolerance and presence of endemic predators may be contributing to the relatively low levels of injury to T. heterophylla caused by A. tsugae. Field surveys of the predator community associated with A. tsugae infestations on 116 T. heterophylla at 16 sites in Oregon and Washington were conducted every 4-6 wk from March 2005 through November 2006. Fourteen uninfested T. heterophylla were also surveyed across 5 of the 16 sites. Each sample tree was assigned an A. tsugae population score ranging from 0 to 3. 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 Fender (Coleoptera: Derodontidae), Leucopis argenticollis Zetterstedt (Diptera: Chamaemyiidae), and Leucopis atrifacies (Aldrich) (Chamaemyiidae) were the most abundant predators; together comprising 59% of predator specimens recovered. Relationships among predators and A. tsugae were determined through community structure analysis. The abundances of Laricobius spp. larvae, L. nigrinus adults, Leucopis spp. larvae, and L. argenticollis adults were found to be positively correlated to A. tsugae population score. Predators were most abundant when the two generations of A. tsugae eggs were present. L. argenticollis and L. atrifacies were reared on A. tsugae in the laboratory, and host records show them to feed exclusively on Adelgidae.

Potential feeding deterrents found in hemlock woolly adelgid, Adelges tsugae

“…Many generalist and several exotic predators feed on HWA (Cheah et al 2004;Kohler et al 2008). Chrysarobin and chrysophanol are known to function in some coleopteran and hemipteran families as feeding deterrents against generalist predators (Kayser 1985;Hilker and Schulz 1991).…”

Comparisons of arthropod and avian assemblages in insecticide-treated and untreated eastern hemlock (Tsuga canadensis [L.] Carr) stands in Great Smoky Mountains National Park, USA

“…Hemlock woolly adelgids were excluded from arthropod diversity and food availability analyses because their size (0.4-1.4 mm in length [Kohler, 2007]) is smaller than typical insectivorous bird prey (Jansson and von Brömssen, 1981, as cited in Pettersson et al, 1995), and there is no documentation in the literature of insectivorous birds preying on hemlock woolly adelgid. Ovisacs and winged forms of hemlock woolly adelgids were analyzed separately from one another because of their different life strategies in hemlocks.…”

Parasitoids Reared From Predators of Hemlock Woolly Adelgid (Hemiptera: Adelgidae), and the Hymenopterous Parasitoid Community on Western Hemlock in the Pacific Northwest

“…In a concurrent study, we surveyed predators associated with A. tsugaeÐinfested western hemlock in western Oregon and Washington for 2 yr to identify potential candidates for A. tsugae biological control in the eastern United States (Kohler et al 2008). Two species of Chamaemyiidae (Diptera) that are specialist predators of adelgids, Leucopis argenticollis (Zetterstedt: Chamaemyiidae) and L. atrifacies (Aldrich), were abundant and seemed to be synchronized with the A. tsugae life cycle (McAlpine and Tanasijtshuk 1972, Greathead 1995, Tanasijtshuk 2002, Kohler et al 2008).…”

“…Two species of Chamaemyiidae (Diptera) that are specialist predators of adelgids, Leucopis argenticollis (Zetterstedt: Chamaemyiidae) and L. atrifacies (Aldrich), were abundant and seemed to be synchronized with the A. tsugae life cycle (McAlpine and Tanasijtshuk 1972, Greathead 1995, Tanasijtshuk 2002, Kohler et al 2008). However, several species of Chamaemyiidae that feed on adelgids, including Leucopis spp., have been shown to be susceptible to parasitism by Þgitid and pteromalid (Hymenoptera) pupal parasitoids, which could limit their effectiveness as biological control agents (Wilson 1938, Brown and Clark 1956, Mitchell 1962, Rao and Ghani 1972.…”

“…In the process of rearing immature A. tsugae predators in the laboratory for our predator study, we observed several parasitoid species emerging from the puparia and cocoons of dipteran and neuropteran predators, including Leucopis spp. (Kohler 2007). Additionally, all hymenopterous parasitoids collected from T. heterophylla in beat samples were identiÞed and counted (Kohler 2007).…”