The fight to save hemlocks

Predator beetles released on Lake George to eat woolly adelgids

By Gwendolyn Craig

On a sunny October day along the shores of Lake George, scientists opened a cooler full of hungry beetles. These black bugs, slightly bigger than a poppy seed, mingled about in noodle-shaped wood shavings inside clear vials. The scientists released them, about 2,000 in all, on the boughs of hemlock trees, hopeful this would be a beetle paradise on Paradise Bay.

Laricobius nigrinus are beetles that eat the invasive hemlock woolly adelgid. Hemlock trees on the eastern shores of Lake George are infested with these aphid insects which kill their hosts over the course of several years. The trees responsible for keeping waters cool for fish and preventing stream bank erosion are found more in the Adirondacks than anywhere else in the state. The state Department of Environmental Conservation is hoping a holy trinity of sorts—insecticide, predator flies and predator beetles—will save the hemlocks from destruction. 

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Hemlock woolly adelgid, native to Japan and brought via ornamental plants to the U.S. in the early 1900s, were first spotted in the Adirondacks in 2017 on the village of Lake George’s Prospect Mountain. The DEC treated the trees with insecticides and thought the population had potentially been eradicated.

 In 2020, a camper at Glen Island on the eastern shores of Lake George, discovered a number of sick hemlock trees. Surveys have now shown the adelgid all along the eastern shore of Lake George north to Black Mountain Point, on The Nature Conservancy’s Dome Island, three of the state’s islands including Turtle, Long and Mohican islands and on the lake’s western shores at DEC’s Hearthstone Campground and private lands.

“We’re not going to stamp out hemlock woolly adelgid,” said Jason Denham, forester with DEC’s Bureau of Invasive Species and Ecosystem Health. “Our goal really is to buy time for the biological controls to take hold, and keep hemlocks on the landscape.”

The New York State Hemlock Initiative, a Cornell University program that receives state funding, is rearing these biological controls that entomologist Mark Whitmore collects from their native habitats in the Pacific Northwest. From a Cornell lab in Ithaca, the team distributes two species of silver fly and the laricobius beetle across the state to hemlock stands infested with woolly adelgid.

On Oct. 27, Whitmore and his team completed their second release of beetles at Paradise Bay, north of Shelving Rock in Washington County. The first release was in the fall of 2020. 

The stand on Lake George was already dotted with dead hemlocks. Denham told the Explorer it is difficult to know the exact cause of a tree’s death, but the combination of adelgids, this summer’s drought and in some cases, spongy moth infestations, has not helped the area’s hemlocks. Whitmore suspected the dead trees at Paradise Bay, some just a few feet off the ground and others growing into the canopy, were victims of woolly adelgid.

“If you can imagine the number of adelgids out here feeding on the trees, the word bazillion comes to mind,” Whitmore said. “We’re just releasing 2,000 of the beetles right now today, so it takes a long time for the population to build up to the point that they’ll be able to control the adelgids.”

Whitmore and Denham are seeing positive signs that hemlocks treated with insecticide are doing far better than those that were not. The DEC has treated trees at the Buck Mountain trailhead and along the eastern shore of Lake George from Paradise Bay to Black Mountain Point. The DEC also treated trees in the Shelving Rock area and on Mohican and Turtle islands. Denham said the treatments should protect the hemlocks for at least five years and up to seven.

Nick Diestschler, research support specialist with the hemlock initiative, said the predatory beetles have already established populations in multiple places in New York. They’re still monitoring how the silver flies are doing. Cornell staff will come back to Paradise Bay in the spring to see if there are signs of their predator bugs.

“I have faith we’ll establish them here given time,” Whitmore said.