Foreign Bug Threatens American Forests

An insect from East Asia is threatening every hemlock tree in the eastern United States, and forestry experts that concerns not just the hemlock tree but the entire forest that the hemlocks help support. The invasive species is called the Hemlock Wooly Adelgid  and it feeds on the starch that hemlocks produce, inhibiting new growth.

“If Hemlock forests continue to decline, we face the loss of species that associate with that type of forests,” says John DiDiego, education director at The Great Smoky Mountains Institute at Tremont. DiDiego has seen much of the damage caused by the insect in Tennessee.

Hemlocks are very important ecologically, as they shade much of the forest, keeping it cool and habitable in the summertime. Loss of the trees has a ripple effect on the entire ecosystem.

“Hemlocks keep temperatures low and moisture high.  Without this effect, salamander and other shade and moisture loving species populations may decline,” adds DiDiego.

Rapidly spreading along the United States east coast, the hemlock woolly adelgid poses a threat to hemlock forests in Georgia.

Kayla Reeves, a natural resources recreation and tourism student in The Warnell School of Forestry, has studied the damage of the adelgid in our area.

“Hiking in the southeast, I’ve noticed several patches where the trees are completely barren. It’s obvious the ecosystem is struggling and it created a creepy scenery,” says Reeves.

A dead hemlock tree stands at the top of Clingmans Dome (North Carolina). The woolly adelgid’s white cotton-like appearance is noticeable on the hemlocks below. Photo by Elizabeth Chambers

The hemlock woolly adelgid covers itself with a white, waxy “wool”—thus infestations are easily recognizable by the appearance of tiny “cotton balls” at the base of hemlock needles.

According to the website of the country’s National Park Service,, the adelgid has infested hemlocks on the Blue Ridge Parkway for about 10 years and in Shenandoah National Park since the late 1980s. Nearly 80 percent of these hemlocks have since died.

The National Park Service is currently issuing three different types of treatments used to kill adelgids: foliar treatments, systematic treatments and predator beetles. Foliar treatments work by spraying the adelgid with insecticidal soap. Systematic treatments work by drenching the soil with insecticide or injecting it directly into the trunk. Predator beetles work by feeding on the adelgid; however, it will take years before beetle populations increase enough to naturally control infestations.

“On a drive up highway 441 through the park, you can see large swaths of dead hemlocks. In the Tremont area, on the hike to Spruce Flats falls, there are lots of dead trees on the hillside,” commented DiDiego. “As far as the spread, this species specializes on hemlock, so wherever there are hemlocks, the adlegid will spread.”

A view out the car window on a drive up highway 441. Photo by Elizabeth Chambers

By: Elizabeth Chambers

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