Hunt for tiny, sap-sucking tree-killer expands to MDI

Posted Jan. 31, 2012, at 6:41 p.m.
Last modified Jan. 31, 2012, at 7:18 p.m.

Staff from the Maine Forest Service will be on Mount Desert Island this week searching for additional infestations of a tiny, sap-sucking bug that is wiping out hemlock groves up and down the East Coast.

The hemlock woolly adelgid — an invasive insect from Asia — has expanded its presence in Maine over the past five years and is now approaching areas Down East where hemlock trees are a common and ecologically important species.

Tree care professionals found two incidents of the insect on MDI last year for the first time, roughly eight years after the bug first was documented in York County, according to the Maine Department of Conservation.

Forest service crews will be paying particular attention to roadside hemlock trees in the villages of Seal Harbor and Pretty Marsh in Mount Desert. Allison Kanoti, a forest entomologist with the state, said there also are plans to survey areas of Acadia National Park with the help of the U.S. Park Service as well as other parts of Hancock, Washington and Waldo counties.

“We have not surveyed these areas in several years,” Kanoti said in a statement issued Tuesday. “And they are vulnerable because of their somewhat more mild winter temperatures, exposure to migrating birds and also late winter-early spring storms can carry the adelgid along the coast.”

Hemlock woolly adelgids are aphidlike insects about the size of a pinhead that attack trees by sucking out sap at the base of the needle. The telltale sign of the adelgid is a white, woolly or cottony substance found on the underside of tree branches at the base of the needles that make the insects look like tiny cotton balls.

Weakened by the adelgid, severely infested trees will turn brown, drop their needles and eventually die. The insect has devastated entire hemlock groves throughout the South and is steadily expanding its range.

Unlike in its native Asia, the adelgid lacks natural predators in the United States and hemlock trees here do not have resistance to the insects. Instead, land and forest managers often treat infected trees with pesticides or release tiny, imported beetles that prey solely on the adelgid, both of which are costly options.

Infested hemlocks have been found in forests in 31 Maine towns, primarily in York, Cumberland, Sagadahoc and Lincoln counties. The two incidences on MDI were on ornamental trees that had been planted more than a decade ago, according to a release from the Maine Department of Conservation.

“The question is whether they were infested when they were planted — it’s hard to know,” Kanoti said in the release. “Or is there something in the forest around them? That’s what we’re trying to find out. That will determine our course of action.”

A new site was found in Alfred in January, representing the farthest inland the woolly adelgid has been located.

Kanoti said winter is a good time of year for landowners to survey for the insects because the egg masses are easier to see and woodland animals have dropped upper branch clippings onto the ground.

Residents who suspect they found hemlock woolly adelgid may contact the Maine Forest Service at 207-287-3147 or forestinfo@maine.gov.

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