Andy Close
WARREN, Pa. – The Forest Service announced the release of a new biological control on the Allegheny National Forest to help combat the non-native, invasive hemlock woolly adelgid.
The recent release of roughly 1,400 silver flies (L. piniperda) in the Tuttle Run and Willow Creek drainages on the Bradford Ranger District was conducted by USFS State, Private, and Tribal Forestry. Made possible with flies provided by Cornell University and Virginia Tech, the fly release is the first of its kind as part of the Allegheny National Forest’s expanded Integrated Pest Management and Hemlock Conservation strategy for the Allegheny Plateau.
Hemlock woolly adelgid (Adelges tsugae) is an invasive forest insect native to Japan and the Pacific Northwest. The adelgid poses a serious threat to eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana), which are at risk of fatal infestations since they lack natural resistance. Within its native range, hemlock woolly adelgid (HWA) populations are kept in check by natural predators, and hemlocks are adapted to the insect. In the eastern US, however, natural predators of HWA are absent and native hemlocks aren’t adapted to the pest.
Until now, HWA biological control has been confined to the release of Laricobius beetles, with roughly 2,500 predatory beetles (L. osakensis) released at various sites across the Forest since 2019.
Biological control (biocontrol) is the use of a natural predator, parasitoid, or pathogen to manage pest populations. Laricobius nigrinus is a predatory beetle species native to the Pacific Northwest where HWA is a natural pest of western and mountain hemlock. Another predatory beetle species, Laricobius osakensis, is native to Japan where HWA is a natural pest of local hemlocks. Additionally, there are two species of silver flies (Leucotaraxis argenticollis and L. piniperda), which are abundant HWA predators in the Pacific Northwest.
Adult Laricobius beetles are released as adults in the fall and feed exclusively on developing and adult HWA throughout the fall and winter seasons while the adelgid is in the first of two annual generations. Adult silver flies are released in the spring, with larvae preying on HWA eggs throughout the adelgid’s spring laying season. When present on the same site in sufficient numbers, the two biocontrols work in tandem for increased HWA predation across multiple lifecycle stages.
