A close up of hemlock woolly adelgid Infestation. GETTY IMAGES PHOTO

Tree-killing insects found at Cobblestone Bridge

MOUNT DESERT — Hemlock woolly adelgid (HWA), a nasty little aphid-like insect, has been found by Land & Garden Preserve staff near the Cobblestone Bridge, a carriage road bridge south of Jordan Pond on the Preserve’s boundary with Acadia National Park. 

White and furry in appearance, the HWA was recently seen coating the branches of large eastern hemlock trees in the area. 

“HWA has been spreading for decades through the southern Appalachian and mid-Atlantic states and more recently into New England,” Tate Bushell, director of natural lands at the Land & Garden Preserve, wrote in the Preserve’s online newsletter. “In 2003 HWA showed up in southern Maine and has been slowly spreading along the Maine coast. 

“WHA is capable of killing its host hemlock tree, and once infestation levels in an area reach a certain threshold, widespread hemlock dieback is common, especially without intervention.” 

HWA kills hemlock trees by attaching themselves to the base of the needles and sucking the sap out of them. 

“Management options include treating individual trees with pesticides, spraying trees with horticultural oil that suffocates the adelgids and…releasing beneficial 

insects that feed on HWA,” Bushell said. “It is too early to know which management strategy the Preserve will pursue, but we are researching all options.” 

He said most of the trees that can be seen from the Cobblestone Bridge are hemlock. 

“Hemlock that live along streams cast deep shade on the water, which has been shown to moderate stream temperature in the summer to the benefit of fish and other aquatic animals,” he said. “If we lose our hemlock, it will certainly impact the ecosystem around the Cobblestone Bridge and will act as a stressor on the forest.” 

If HWA isn’t already in Acadia, it is probably just a matter of time, especially with an infestation now on its doorstep. 

Acadia staff wrote in a 2021 article that shade cast by hemlocks creates an ideal environment for small freshwater invertebrates. 

These invertebrates are the major food source for the many different species of freshwater fish that we have here at Acadia, such as brook trout,” they wrote.  

“So, when the hemlocks eventually die from an HWA infestation, the invertebrates can no longer thrive there, and we see a decrease in freshwater fish populations. This, of course, causes even more issues going up the food chain, so that one tiny insect is affecting an entire ecosystem.” 

Vehicles, horses or anything else that comes into contact with infested branches can pick up the adelgids and move them to new areas. To try to prevent that, Land & Garden Preserve staff have been pruning back hemlock branches that were hanging over carriage roads. 

Bushell recommends that people keep a close eye on the hemlocks on their property for signs HWA, especially if new trees have been trucked in from points south. 

But are monitoring and prevention efforts just delaying the inevitable? 

All the way back in 2010, scientists with the Rocky Mountain Climate Organization and the Natural Resources Defense Council wrote a 42-page report titled “Acadia National Park in Peril: The Threats of Climate Disruption.” 

“Warmer winters…are promoting the spread of a tree-killing insect from Asia, the hemlock wooly adelgid, believed to be on its way to eliminate eastern hemlocks from the Northeast,” they wrote. 

“The loss of the hemlocks from global warming’s combined effects on habitat availability and HWA infestation threatens to destroy the entire ecosystem, leading to an irreversible loss of North American biodiversity.” 

The Maine Forest Service website has information about identifying invasive species including HWA and what to do if you find them. 

Dick Broom

Dick Broom

Reporter at Mount Desert Islander
Dick Broom covers the towns of Mount Desert and Southwest Harbor, Mount Desert Island High School and the school system board and superintendent's office. He enjoys hiking with his golden retriever and finding new places for her to swim. [email protected]
Dick Broom

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