Researchers release bugs in strategy to save Adirondack hemlocks
By Gwendolyn Craig
Hemlocks are dying near Paradise Bay. The Lake George cove is lined with their lacy branches dangling dark green above the water. Steps from the shore and into the forest, the canopy thins. Brown needles have fallen from branches leaving behind brittle skeletons. Nibs of lime green, the sign of new growth, cannot be found.
Mark Whitmore looks up.
Then he looks down to forage mushrooms, disappearing for a while. There must be some good news in a place called Paradise. Alas, on this October day, he comes back mushroom-less. Instead, the entomologist is holding a hemlock limb dotted with white puffs. These are the tree killers.
Whitmore is the principal investigator of Cornell University’s New York State Hemlock Initiative. He has studied tree-eating insects for over three decades. The hemlock woolly adelgid has become his specialty. The bug is native to the Pacific Northwest, China and Japan. Scientists believe woolly adelgid was brought to the eastern U.S. on Japanese ornamental plants in the early 1900s.
The invasive insect, so tiny it spreads on the wind, was first spotted in the Adirondacks in 2017 on Prospect Mountain in Lake George. Insecticides tamped them down, but in 2020, a camper found a sample on the eastern lakeshore at Glen Island Campground. Jason Denham, forester with the state Department of Environmental Conservation’s Bureau of Invasive Species and Ecosystem Health, said surveys now show adelgids are on hundreds of acres. The discovery was particularly alarming to state and local researchers because hemlocks are one of the most prevalent trees in the watershed and make up about 10% of the trees in the Adirondacks.
Woolly adelgids are formidable. They are all females that lay eggs without fertilization. Only one is needed to start an infestation.
“It’s impossible to keep it out of a forest in my opinion,” said David Orwig, an ecologist overseeing woolly adelgid research at Harvard Forest in Petersham, Mass. and around southern New England.
At Lake George, researchers have detected adelgids along most of the southeastern shore and as far north as Black Mountain point. On the western shore, the bugs have settled on private property and at the DEC’s Hearthstone Campground. The insects have infested trees on Long Island, Turtle Island, Mohican Island and The Nature Conservancy’s Dome Island.
“We’re just beginning to see mortality here at Paradise Bay, and I expect it to mount as the population of the adelgid grows,” Whitmore said.
In this sick ward of trees, Whitmore, Denham and other scientists are throwing everything they’ve got at the adelgids to save their patients. It’s a recipe of treatments still under trial—a short-term shot with insecticide to save some hemlocks, mixed with a long-term prescription of two adelgid predators, biological controls in the form of flies and beetles from the Pacific Northwest. The management trifecta is endorsed by the U.S. Department of Agriculture.
In a perhaps unusual twist, climate change could also play a role in hemlock survival, though it’s not a particularly welcome solution to scientists, nor is it reliable. Adding to the uncertainty is a pending bill in the state Legislature banning some insecticides that could shorten one leg of this treatment stool.
“We’re not going to stamp out hemlock woolly adelgid,” Denham said. “Our goal really is to buy time for the biological controls to take hold and keep hemlocks in the landscape.”
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Carrie Jubb understands why some shudder at the thought of introducing a new species to control another. Jubb is the insect quarantine officer at Virginia Tech’s Beneficial Insects Containment Facility.
Biological controls have sometimes backfired—for example, the cane toad. The poisonous toad, native to South and Central America, was introduced in the 1930s to Australia with the idea that it would eat beetles decimating sugar cane fields. But cane toads feed on the ground at night, and the beetles visits tall stalks of sugar cane during the day. Not only were they an ineffective biological control, but the toads also became a nuisance, eating native species and free of predators.
In the U.S., the multicolored Asian lady beetle was introduced to eat agricultural pests with mixed results. While a successful predator, the beetles upset homeowners when they swarmed in and on residences in the fall.
With bolstered U.S. biological control regulations, came better results. A fungus used against the booming populations of spongy moth helped destroy the defoliating caterpillar. Insects released to snuff out purple loosestrife have kept the invasive plant’s numbers down. Now, preliminary evidence is showing that a predator beetle of the hemlock woolly adelgid may join the list of successes.
How does one get permission to release a biological control?
Jubb said researchers first visit the native homes of the invasive species, look for natural enemies and get permission to collect and study them in a lab.
Beginning in the 1990s Virginia Tech studied the woolly adelgid’s predator beetle, Laricobius nigrinis, examining its lifecycle and habitat and experimenting with its feeding preferences. The researchers found the beetles exclusively ate the woolly adelgids and did not impact other species, leading them to get the USDA’s Animal and Plant Health Inspection Service’s permission to release the bugs.
From 1985 to 2015, according to the U.S. Forest Service and USDA, 50% of the 75 projects against invasive insects were effective.
At the Virginia Tech lab, Jubb said, “we’ve been housing a weevil in our facility for over 15 years that is being evaluated as a biological control of tree-of-heaven.” Yet, the weevil has not been authorized for release because it can feed on other plants found in southern states.
“With the recent introduction of the invasive and highly destructive spotted lanternfly, whose primary host is tree-of-heaven, there may be more motivation to have this weevil released to help control this invasive tree species,” Jubb said.
How to report sightings
Send photos and location of suspected invasions to NYS DEC at email@example.com or call the Forest Health Information Line at 1-866-640-0652. Or use iMapInvasives, a partnership between state agencies and the SUNY College of Environmental Science and Forestry: www.nyimapinvasives.org
Lake George releases
Whitmore’s lab at Cornell is rearing its own biological controls—Laricobius beetles, and two species of leucotaraxis silver flies, which Whitmore collects from hemlocks in the Pacific Northwest.
The two predators attack different generations of the adelgids (there are two annually). Laricobius beetles feed on the first generation and lay their eggs in the second, overwintering generation, Whitmore said. The flies will also feed on the overwintering generation’s eggs. Most importantly, Whitmore said, the flies feed on the nymphs and eggs of the second generation, something the Laricobius beetles do not do.
The silver flies are more experimental and have yet to establish populations in New York. The beetles have had more time to show promise.
On the eastern shores of Lake George, the hemlock initiative released 620 Laricobius beetles in 2020 and 1,999 in 2022. For silver flies, it released 1,418 Leucotaraxis argenticollis in 2021 and 974 Leucotaraxis piniperda in 2022. Nick Dietschler, a research support specialist with the initiative, said the region has received one of the largest release totals of predator bugs in the state and is one of a few sites where all three predator species were released.
On Oct. 27 at Paradise Bay, the hemlock initiative team, including Whitmore, Dietschler and Jasmine Schmidt, took out vials of predator beetles from a cooler. These hungry black bugs, held within noodle-shaped wood shavings, were placed on the boughs of adelgid-infested hemlocks in hopes that they will eat, mate and lay eggs.
“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.”
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Time is no strange ingredient when bolstering biological control populations. The release of a fungus to control spongy moth, for example, was first tried in the early 1900s. It wasn’t until 1989 that the fungus was found killing the caterpillars in Connecticut, according to Cornell University.
Laricobius beetles are establishing populations in New York much more quickly, though Whitmore said releasing 500 to 1,000 “visitors into the forest” is hardly “storming a castle.” The hemlock initiative crew started releasing the beetles in New York in the fall of 2008 and spring of 2009. Whitmore said he found evidence that the Laricobius beetles were reproducing by the fall of 2009.
The initiative has confirmed beetle establishment at 13 locations in New York, Dietschler said, including in the Finger Lakes, Lake Ontario, Lower Hudson Valley and on the Shawangunk Ridge southeast of the Catskills.
Jubb has found the beetles are even more successful in warmer climes. About 82% of Virginia’s release sites have established beetle populations.
“It may take a little longer for populations to build in northeastern states,” Jubb said. “Climate change may speed that up.”
Insecticide and policy concerns
In hopes of buying the beetles and flies time, the DEC has treated 6,369 hemlock trees with insecticides called imidacloprid and dinotefuran in the Lake George area since 2020. Denham said some trees are sprayed on their bark. Others closer to the water get a direct injection. The insecticide travels up into the trees’ limbs, where eventually adelgids will feed and be poisoned. The treatments should last at least five years.
Denham and Whitmore said treated trees from 2020 look much healthier than the untreated trees.
State legislation could hinder this stopgap.
State Sen. Brad Hoylman, a Manhattan Democrat, is the sponsor of the Birds and Bees Protection Act. The bill would prohibit the sale, use and distribution of certain pesticides, including imidacloprid and dinotefuran. The bill’s justification cites a Cornell University state-funded report showing that the pesticides are toxic to pollinators.
Denham said the way DEC applies the chemicals to hemlock presents “extremely little chance of drift” to impact pollinators. Without the insecticides, there’s no other chemical tool, Denham added.
“It would really handcuff us, and we’re concerned about that,” Denham said.
At the Adirondack Park Invasive Plant Program summit in Blue Mountain Lake in October, Whitmore also expressed his concerns about the bill and the importance of the chemical treatments. They’re “really keeping some of our most cherished hemlock stands alive right now,” he told attendees.
The legislation does contain a clause that says the DEC could use chemicals in emergencies to control or prevent invasive species, though it outlined a consultation process and deadline for its use. The Explorer asked Hoylman’s spokesperson if the hemlock treatments would be considered emergency use. The spokesperson declined to comment.
The Explorer asked Whitmore and the DEC about the emergency clause. The DEC said it does not comment on pending legislation. Whitmore also declined to comment but noted legislation could be amended.
Orwig said he’d hate to see New York ban the chemicals and didn’t see how the hemlock treatments could impact pollinators since the trees are not pollinated by insects. He recommended a specific exemption in the bill for woolly adelgid treatment.
Chemicals are the most accessible tool for private landowners with sick hemlocks. Tammara Van Ryn, program manager of the Adirondack Park Invasive Plant Program and Monica Dore, conservation project manager for the Lake George Land Conservancy, said there is a shortage of pesticide applicators and few programs for financial assistance.
“We can always use more of everything,” Denham said. “We have a lot of staff that are trained, then licensed as pesticide applicators from other programs that lend their time to hemlock woolly adelgid during the right window to treat that pest.”
Denham said some trees were treated at Hearthstone Campground this year, but more needed to be done. Van Ryn noted that the DEC did not have the staff to treat hemlocks at Hearthstone when woolly adelgid was first discovered there in 2021.
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The role of climate change
The impacts of climate change could also play a part in this drama. Adelgids typically don’t survive well in the cold and neither do their predators. As the planet warms, however, woolly adelgid populations are marching further north.
The Adirondacks’ colder temperatures could be a blessing, especially in areas that reach minus 30 degrees. Whitmore has witnessed adelgid mortalities in cold snaps. But that could also mean the Adirondacks is a laboratory for a superbug. Those adelgids that do survive pass on their resistance to the next generation, creating a heartier population.
“Wild swings” in temperature, Orwig said, could negatively influence the adelgids. He predicts the invader will spread in the Adirondacks, “but the impact on hemlock will be much slower than what we’ve seen further to the south.”
In another unlikely hero situation, heavy rain caused by climate change could also produce an adelgid predator—fungus. “High rainfall facilitates fungal infection” of adelgid nymphs, a 2021 paper by Orwig with researchers from the University of Massachusetts Amherst stated. Orwig said the naturally occurring fungus could be another form of biocontrol.
Though interested in preserving and protecting hemlocks, Orwig is focused on watching the transformation of hemlock stands impacted by woolly adelgids. Using monitors of carbon fluxes in tree canopies, Orwig and his colleagues are measuring how the demise of hemlock trees could become sources of carbon emissions.
Gary Lovett, a forest ecologist at the Cary Institute of Ecosystem Studies, has modeled how hemlock stands may change from carbon sinks, storing the gas, to carbon emitters. But something will take the hemlocks’ place. Lovett’s models show increased carbon sequestration 100 and 200 years in the future, well beyond levels from when the hemlocks thrived.
“Timeframe matters,” Lovett said.
He worried more about nutrient impacts from dying hemlocks. Since hemlocks are known for preventing streambank erosion and for soaking up nitrogen, a die-off could lead to nutrient leaks into streams, a “nitrogen bomb,” Lovett said. With warming waters from climate change, the loss of shade from hemlocks and an increase of nutrients, more algal blooms could result.
It’s a concern for Dore at Lake George, whose waters recently rippled with cyanobacteria blooms, also called harmful algal blooms.
Unused nitrogen gets absorbed quickly by other plants, Orwig said. He wasn’t sure if there would be an increase in algal blooms, though he said it was possible.
In New England, Orwig saw black birch, sugar maple, red maple and red oak take the place of hemlocks. He thought beech trees could replace some hemlock stands in the Adirondacks were it not for beech leaf and bark disease (see page 16). Lovett warned that another looming invasive species threat—the Asian longhorn beetle—is killing maple trees. It has not yet been reported in the Adirondacks. Its arrival would be “our nightmare scenario,” he said.
In a visit to the High Peaks, Orwig identified a 448-year-old hemlock in Keene, perhaps the oldest known member of its species in the Adirondacks. It appeared untouched by the adelgid.
“They live for centuries,” Orwig said, “and now, they may be potentially wiped out.”
But if some hungry beetles and flies have success at Paradise Bay, maybe not.