Hemlock Beetle Battle

UT’s Beneficial Insects lab steps up production to combat the adelgids killing hemlocks

UT's Beneficial Insects lab steps up production to combat the adelgids killing hemlocks.

Photo by E. Bernard, University of Tennessee

UT's Beneficial Insects lab steps up production to combat the adelgids killing hemlocks.

While the sap-sucking woolly adelgid is laying waste to eastern and Carolina hemlocks in the forests of Southern Appalachia at an alarming pace, scientists at the Lindsay Young Beneficial Insects Laboratory at the University of Tennessee are working just as furiously to produce predator bugs that can demolish the invaders.

At the urging of the U.S. Forest Service and under the direction of Dr. Pat Parkman, the four-laboratory complex produced 213,000 Sasajiscymnus tsugae and 20,000 Laricobius nigrinus, two beetles that devour the aphid-like adelgids, between November 2006 and June 2007. That’s more than twice the number of St beetles the lab had produced in a single year since opening in 2004, and almost 10 times more Lari beetles than the previous year.

“We’re using a living organism to control a pest organism—a biological control,” says Parkham, who joined the project in November 2006. “There’s evidence that when both beetles are established, especially the Lari beetle, and established when the infestation is just beginning, they can control the adelgid to the point where the trees don’t die. They won’t be the healthiest looking trees, but...”

Adult beetles are packed about 2,500 per plastic gallon container, along with hemlock foliage, to be released by the U.S. Park Service, Forest Service, and, sometimes, state wildlife organizations, and start devouring. “The beetles particularly like adelgid eggs, because they’re the most nutritious, which is good because the larval stage does the most damage to the hemlocks,” says Parkman. “And they also eat adelgids in the nymph and adult stages.”

Hemlocks can reach 165 feet and live more than 900 years, and adelgids first started interrupting that life cycle in northern U.S. trees. The tiny bugs advanced to this area with wind, migratory birds, and humans—and the trees in the South are failing much more quickly than expected, says Parkman. “The destruction is happening a lot faster because the predictions were based on what happened up north, where a tree might take seven to 14 years to die, and down here a tree can die in three years,” says Parkman. “We don’t have those long, cold winters that will kill the adelgids and prevent them from reproducing.”

Along with donors such as the lab’s namesake, Lindsay Young, the beetle-producing project has received support from organizations like the Friends of the Smokies, which gave the kick-start grant to get the lab producing.

And the beetles are just one facet of the fight to save the hemlocks. Where they’re able to drive to the trees, the National Park Service also employs pesticides. “If it’s a place like Cades Cove, where it’s convenient to drive up once a year, they can use insecticidal soap,” says Parkman. “A soil drench, which is taken up by the trees through the roots, will last three to four years.” But those are just for areas with easy motor access—the beetles have the advantage of being able to ride in a backpack.

Right now, Parkman’s team is working furiously to produce as many beetles as possible, but while they’re expending the same effort and hours they did in 2006-2007, the beetle yield is down some for this year. “I believe that is due to the drought,” says Parkman. “The food quality for our beetles is just not as good as it was the previous year—it’s tough to find lush, infected hemlock branches for them to feed on.”

The goal, for the lab and all the conservationists involved, is no longer to save all the trees—the destruction has gone too far for that. But saving even enough of the hemlocks to preserve the species would be a global triumph, and Parkman is hopeful hundreds of thousands of little bugs might be able to eat their way to victory. “We haven’t done much follow-up on results,” he says. “So far all our effort has gone into producing and releasing the beetles.”

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