ANF turns to silver flies to help thwart HWA

Photo provided by the U.S. Forest Service Danielle Kelley, U.S. Forest Service forest health technician, attaches a silver fly release tube to a hemlock bough in Allegheny National Forest.

The fight against an invasive insect now includes the introduction of another insect.

Talk about fighting fire with fire.

The Forest Service has released a new “biological control” in the fight against hemlock woolly adelgid — silver flies.

HWA is an invasive forest insect native to Japan and the Pacific Northwest.

“Within its native range, hemlock woolly adelgid populations are kept in check by natural predators, and hemlocks are adapted to the insect,” ANF Public Affairs Officer Chris Leeser said. “In the eastern US, however, natural predators of HWA are absent and native hemlocks aren’t adapted to the pest.”

Federal officials have released about 2,500 Laricobius beetles around the ANF since 2019 in an attempt to thwart the HWA.

This effort — about 1,400 silver flies at a couple sites on the Bradford Ranger District — was conducted by Forest service, state, private and tribal foresters.

“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,” Leeser said.

A biological control is exactly what it sounds like — using a natural predator or pathogen to manage pest populations, according to the ANF.

The beatles previously released are native to the Pacific Northwest, as are two species of silver flies.

“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,” Leeser explained. “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.”


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