WARREN, Pa. – The US Department of Agriculture, 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 (HWA).
Hemlock woolly adelgid (Adelges tsugae) is native to Japan and the Pacific Northwest. The adelgid poses a serious threat to eastern hemlock (Tsuga canadensis), which are at risk of fatal infestations since they lack natural resistance.
The release of approximately 1000 Laricobius nigrinus beetles occurred at a single site in the Bradford Ranger District near Baughman Run. The release, made possible with beetles provided by Virginia Tech University, was conducted by the USFS State, Private, and Tribal Forestry organization alongside staff from Allegheny National Forest (ANF).
Within its native range, 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 are not adapted to the pest.
To combat HWA, biological controls can be utilized. A biological control (biocontrol) is the use of a natural predator, parasitoid, or pathogen to manage pest populations. Two species of beetles (Laricobius nigrinus and Laricobius osakensis) also native to Japan and the Pacific Northwest, are known for being abundant predators of HWA. These biocontrol beetles prey on the first generation of HWA each year, both HWA adults and eggs.
The four species of insects that are effective biological controls for HWA are Laricobius nigrinus, Laricobius osakensis, and silver flies (Leucotaraxis argenticollis and Leucotaraxis piniperda). Laricobius nigrinus is the third biocontrol species released on ANF as part of an Integrated Pest Management and Hemlock Conservation strategy for the Allegheny Plateau.
Collaborative efforts in 2019 led to the successful establishment of Laricobius osakensis beetles on ANF. Those beetles are now being relocated in small numbers to other prioritized areas of the forest for establishment. Additionally, adult silver flies (L. piniperda) were released this spring, their larvae prey on HWA eggs throughout the adelgid’s laying season.
When present on the same site in sufficient numbers, the three biological controls work in tandem for increased HWA predation across multiple lifecycle stages.