Saving Hemlocks from Extinction

Jan 16, 2014

A tiny, invasive bug is bringing down hemlock trees from Appalachia to southern Canada. And scientists fear another treasured native tree may be going the way of the American chestnut, forever changing forest ecosystems.

Researchers at Virginia Tech are hoping to beat the invaders at their own game. They’re using a new invasive species to keep an old one in check, and save the American hemlock tree.


The bright green needles of evergreen trees shine this time of year unfazed by the cold, even as most of the forest is down for its winter nap. But a life and death battle between titans of the insect world is underway ---and the prize will be the country’s hemlock trees.

But while Hemlocks are not an economically important tree, Virginia Tech Entomologist,Tom McAvoy says they’re extremely ecologically important.  “Hemlocks in the east provide a unique habitat, and no other plant species can replace it. They shade streams in the mountains that keep the temperature cool in the water. It affects trout populations. It affects a lot of breeding birds that require hemlocks to nest in.”

But for decades an invasive insect, originally from southern Japan, has been sucking the sap out of the trees in eastern North America.  The pest is known as the Woolly Adelgid, for the telltale white puffs it leaves on the base of the needles.

“The Adelgid was first noticed in the early 1950s around the area of Richmond," says Entomology Professor, Scott Salom,  Virginia Tech’s lead researcher on the project to save the Hemlocks. He says it took about 30 years for the foreign invaders to gain a foothold here.  “And all of a sudden the spread was on, it made it to Connecticut, devastating trees in Connecticut, it started devastating trees in Virginia like the Shenandoah National Park lost of lot of old growth Hemlock and it became a visible pest.”

But now the Woolly Adelgid’s old nemesis from her home turf back on her trail. And After careful selection, testing and 7 years of quarantine a predator beetle from Japan has been released in a test forest at Virginia Tech.  It’s mission; under controlled conditions, bring down the Adelgid that’s killing the Hemlocks in this 1 acre test area. And it’s this time of year when the battle heats up.

“When everything shuts down, the leaves are off the trees everything is going dormant, the adelgids wake up, are starting to grow and they’re going to continue to grow through winter. And here’s a predator that sleeps in the summer and wakes up when its prey wakes up, and becomes active when host is available," says Salom.

And this is key when it comes to fighting one invasive species by using another. Timing is everything.  And rather than a winner, a state of balance between the competitors is the goal.

“But it’s a long term project. And this is really our only solution for forest environments, is to bring that predator complex from its native environment, and allow the insects to control the adelgids and keep it under control," says McAvoy.

Come spring, the question will be, have the newcomers taken a seat at the table, joining the local insect food chain and giving the Eastern hemlock a chance at survival.