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(WBIR - Great Smoky Mountains) If you are able to tolerate the cold temperatures, winter can be an incredible time of year to take a hike in the Great Smoky Mountains National Park. Visibility soars in the crystal clear air and there are hardly any bugs. That is, except the invasive hemlock woolly adelgid insect that has infested and killed millions of the mightiest trees in the eastern United States.

"This time of year, the hemlock woolly adelgids are awake. They are feeding on the Hemlock needles during the winter time. They actually hibernate during the summer," said Jesse Webster, a forester who coordinates the GSMNP program to control the hemlock woolly adelgid. "You see what looks like snow on the underside of the hemlock branches on the needles. Each one of those little cotton balls is a female in that woolly mass sucking the carbohydrates out of the tree."

Hemlock woolly adelgids (HWA) have devastated some of the mightiest trees in the forest since it was first identified in the national park in 2002. The invasive insect from Japan has not only benefited from the absence of natural predators, but also thrived in the relatively mild winters during the last decade.

"When we really saw the adelgid spread so fast across the Southeast was in 2007 and 2008 when we had extreme drought and warm temperatures," said Webster. "There is a reason these insects have not thrived in places farther north than Vermont and Maine. They cannot withstand prolonged periods of extremely cold temperatures."

The recent stretch of frigid conditions is finally punching back at the insect that has threatened the very existence of the hemlock.

"The HWA starts to see real mortality at a threshold of around 5 degrees Fahrenheit. We saw this morning, Mt. LeConte register temperatures at -10 degrees and a few weeks back it was down to -17 degrees," said Webster. "In a lot of the higher elevations, we are seeing mortality rates on the adelgids from 50 up to 100 percent. They have that white woolly mass that they are named for to protect them from the cold, but it is difficult for them to survive when it gets that cold for a long duration of time."

Webster refers to the recent cold snap as a "reset button" for a pest that has mostly run roughshod through millions of hemlock trees during the last decade. The national park has treated some trees with pesticides to stem the tide of adelgids.

Biologists have also released beetles from Japan and the Pacific Northwest that serve as natural predators to feed on the hemlock woolly adelgid. Webster said those insects should be able to survive the recent extreme weather.

"The beetles are larger and hardy enough that they can live through these frigid conditions better than adelgids," said Webster.

Webster examined the branches of a hemlocks using a microscope attached to a large television monitor. As he went down each needle of one branch, he had to search for survivors.

"Almost all of these are dead. They have frozen to death. If you look here, there is one individual that actually made it through the cold snap. But again, on this one branch you could be looking at up to 80 percent mortality."

While Webster says nothing will get rid of the adelgids completely, this winter is the first time the invader has dealt with Mother Nature's icy grip of death.

"This is encouraging we've had this real big cold snap. And the winter's not over. We're probably looking at a pretty good setback on adelgid numbers."

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