The US Department of Agriculture, Forest Service announced the release of additional beneficial insects in the Allegheny National Forest to combat the non-native, invasive hemlock woolly adelgid.
Hemlock woolly adelgid (HWA) is an invasive insect native to Japan and the Pacific Northwest. The adelgid poses a serious threat to eastern and Carolina hemlock, which are at risk of fatal infestations since they lack natural resistance. Within its native range, HWA populations are kept under control by natural predators and hemlocks have adapted to the insect. However, in the eastern United States, natural predators of HWA are absent and native hemlocks are not adapted to the pest.
Biological control (biocontrol) is the use of a natural predator to manage pest populations. Four insect species are known to be effective biocontrols for HWA; predatory beetles (Laricobius nigrinus and L. osakensis) and silver flies (Leucotaraxis argenticollis and L. piniperda). These species are native to the Pacific Northwest and Japan, where HWA is a common pest of local hemlocks.
Laricobius beetles are released as adults in the fall and feed exclusively on developing and adult HWA throughout the fall and winter while the adelgid is in the first of two annual generations. Leucotaraxis flies are released as adults in the spring, with larvae preying on HWA eggs throughout the adelgid’s laying season. When present on the same site in sufficient numbers, the two biocontrols work in tandem for increased predation across multiple HWA life cycle stages.
During October and November, more than 2,000 predatory beetles were released at several sites across the Bradford Ranger District of Allegheny National Forest.
In early October, roughly 1,000 L. nigrinus beetles were released at two sites near Yellow Hammer and Muzette.
In early November, roughly 1,000 L. osakensis beetles were released at two sites near Hector Falls.
Previous HWA biocontrols were used in the Allegheny National Forest as part of the Integrated Pest Management and Hemlock Conservation strategy for the Allegheny Plateau. Since 2020, approximately 5,600 predatory beetles and 7,300 predatory flies have been released at more than a dozen sites across the forest. All flies and beetles were provided by Cornell University and Virginia Tech, with technical support from US Forest Service State, Private, and Tribal Forestry.
