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.

Forest health monitoring in transition: Evaluating insect-induced disturbances in forested landscapes at varying spatial scales

“…The early symptoms of HWA infestations are defoliation and reduction in shoot growth (Kohler et al 2008). Infested hemlocks often die in a span of four to 10 years (McClure et al 2001;Spaulding and Rieske 2010).…”

Circumventing regulatory safeguards:Laricobiusspp. and biocontrol of the hemlock woolly adelgid

“…Propagation difficulties and apparent differences in its interactions with HWA infesting different hemlock species prevented its use . Biocontrol efforts now focus on predators, but citations associated with assertions that biocontrol agents successfully control HWA in its native range (e.g., McClure, 1995aMcClure, ,b, 1996McClure, , 1997Cheah & McClure, 1996, 1998Sasaji & McClure, 1997;McClure et al, 2000;Kohler et al, 2008aKohler et al, ,b, 2016 refer to correlative studies that include few or no data about population-level effects in the field. The presence of a predator does not necessitate its interaction with and population impact on prey (Van Driesche & Hoddle, 2017).…”

A Little Bug with a Big Bite: Impact of Hemlock Woolly Adelgid Infestations on Forest Ecosystems in the Eastern USA and Potential Control Strategies

“…The ideal candidate predators for HWA should be found in the pest’s native range of Japan, eastern Asia or the pacific northwest of the USA. Up to 50 species of generalist and specialist predators of HWA have been identified in Japan or eastern Asia [119]. Several predators have been tested for biological control potential since 1992 [17,90,119,120,121,122,123,124,125,126,127,128,129,130].…”