March 13, 2026

DEC, OPRHP, and New York State Hemlock Initiative Announce Major Milestone in Hemlock Woolly Adelgid Biological Control

The New York State Department of Environmental Conservation (DEC), the New York State Office of Parks, Recreation and Historic Preservation (OPRHP), and Cornell University’s New York State Hemlock Initiative (NYSHI) today announced confirmation that Laricobius nigrinus, a predator beetle being released to control the invasive hemlock woolly adelgid (HWA), is reproducing successfully in the lower Hudson Valley.

“Hemlocks are a foundation species in New York’s forests, providing critical habitat for wildlife, supporting water quality, and stabilizing soil on steep slopes,” said Justin Perry, DEC’s Invasive Species and Ecosystem Health Bureau Chief. “Their conservation is a priority for New York State, and successful biological control efforts like this collection strengthen ongoing, science-based work to manage HWA through integrated pest management strategies.”

Teams from New York, New Hampshire, and Vermont collected 12,676 of the sesame seed-sized beetles from Harriman State Park, where they had been released years earlier as part of a regional HWA biocontrol effort. The number collected exceeded expectations and marks significant progress towards establishing HWA population controls.

The effort to establish Laricobius nigrinus populations at Harriman State Park began with releasing approximately 2,000 beetles in 2018, 2019, and 2020. Beetle population growth must occur in the wild in order to successfully expand across landscapes without ongoing human assistance. This year’s record beetle collection has allowed for the redistribution of beetles to new sites across New York and neighboring states as part of a cooperative effort to establish new populations of HWA predators across the northeast. Partners from New Hampshire and Vermont collected 4,392 and 1,437 beetles, respectively, to release in their states. New York benefitted from a similar effort in North Carolina in 2013. Nearly 6,500 beetles were released at three New York sites: Long Point State Park, Thacher State Park, and DEC’s Five Rivers Environmental Education Center.

OPRHP Assistant Division Director for Environmental Stewardship Lynn Bogan said, “Through the hard work and dedication of our State Parks team, our partners at the DEC and Hemlock Initiate, and the successful biocontrol, we continue to make great progress toward hemlock conservation. We are grateful for this and will continue to work with our partners across New York State and neighboring states. We encourage the public to help protect hemlocks by identifying and reporting HWA sightings to https://www.nyimapinvasives.org.”

Forest Health Researcher at Cornell University's New York State Hemlock Initiative Nicholas J. Dietschler said, “The Harriman collection was remarkably productive, yielding thousands of beetles from about a 50-acre search area. Given that we’ve confirmed natural Laricobius spread up to 15 miles from the site, the total population on the landscape is hard to comprehend, which is a great sign for biological control of HWA.”

These established populations offer hope for hemlock forests in the Lower Hudson Valley and provide a local beetle resource for future collect-and-release operations to support hemlock conservation in more northern areas of New York and beyond.

HWA is an invasive insect that can attack healthy hemlock trees, often killing them in under a decade. It was discovered in the lower Hudson Valley and on Long Island in the 1980s and has since spread north to the Adirondacks and west to the Finger Lakes Region. Efforts to control HWA largely involved early detection and chemical control, but these are not long-term solutions.

Establishing specialist predators, like Laricobius nigrinus, will help keep HWA populations in check naturally, allowing hemlocks to survive. Public involvement remains essential to protecting hemlocks and anyone can help by learning to identify and report HWA using resources from the New York State Hemlock Initiative or DEC.

For questions or resources on hemlock conservation, visit the New York State Hemlock Initiative (NYSHI) website or email [email protected].

Image Credit Photo Courtesy NYSDEC

DEC Forester Erica Culbert collecting the predators.

Image Credit Photo Courtesy NYSDEC

HWA Infestation Closeup

Image Credit Photo Courtesy NYSDEC

HWA at Willow Point

Image Credit Photo Courtesy NYSDEC

HWA Wool

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