An invasive insect is killing Pennsylvania’s state tree, the eastern hemlock, and the Western Pennsylvania Conservancy is trying a ‘biological solution’ to prevent its spread.
Charles Bier, the Conservancy’s director of conservation science, is leading the charge to create an “insectary” at the Bear Run Nature Reserve in the Laurel Highlands.
“An insectary is basically a nursery habitat where you grow insects,” he explains.
LISTEN: Could These Tiny Beetles Save PA’s Hemlocks?
Bier points out why an insectary is needed here. A graceful, pyramid-shaped evergreen sits in one of the few green spots in the chilly spring forest. But some of soft, flat needles are looking a little sparse. Bier looks at the underside.
“You can see right there, that’s definitely hemlock woolly adelgid,” he says.
Hemlock wooly adelgid look like tiny white balls of cotton, clinging where the stem meets the base of the hemlock’s short needles. The aphid-like adelgids, native to Japan, were first found in the eastern U.S. around 1950, and have decimated hemlock trees in the southern Appalachians and Great Smoky Mountains. Once infested, a tree might only last a few years.
“You’ll start to see it with branches no longer holding needles, and eventually the tree is just a skeleton, and it dies,” Bier explains.
Eastern hemlocks grow near streams, and provide shade for brook trout. Many birds, like the blackburnian warbler and yellow bellied sapsucker, rely on hemlock habitat.
Adelgids have been in the eastern half of Pennsylvania for years, but now they are moving westward. Andy Zadnik is the director of land stewardship for the Western Pennsylvania Conservancy. He says around 2009, they were found here in the Laurel Highlands at historic Fallingwater and Ohiopyle State Park.
“When we heard it was in Ohiopyle, we knew it was just a matter of time until it make it here to Bear Run Reserve,” he says.
There is an insecticide that helps control adelgids, but Zadnik says it’s been difficult to treat enough trees.
“You have to pick one tree vs. another tree, because it’s very labor intensive and very expensive to treat these individual trees with a chemical,” he says.
Enter the “Insectary”
Zadnik hikes across a parking lot, up through tall dry grass, and finds a few small shrubs protected by a small orange deer fence.
“Twelve little hemlocks,” he laughs.
This insectary might not look impressive, but the Conservancy is betting it will save native hemlocks at Bear Run. Working with state foresters, they will care for these nursery plants, preparing them to be purposely infected with adelgids. If the adelgids take hold in the nursery, the Conservancy will introduce a predatory beetle, the Laricobius nigrinus(Ln), to feed on them.
“We just need to get this predator here to stop the hemlocks from dying in large numbers”
The idea comes from Cornell University, where researchers have determined that this kind of beetle aggressively eats hemlock woolly adelgids. The Conservancy’s plan is to raise a population of Ln beetles and then release them more widely into Bear Run. The hope is that the beetles will spread, eating adelgids off the hemlocks.
Ln beetles are native to the Pacific Northwest and northern Rocky Mountains, and they already exist in eastern Pennsylvania, but they are not native to this region.
“We just need to get this predator here to stop the hemlocks from dying in large numbers,” Bier says.
Is it really a good idea to release a non-native beetle into the forests?
Mark Whitmore is the forest entomologist from Cornell University who has been working with the USDA on regulations for releasing Ln Beetles to prey on adelgids. He says researchers have already learned the hard way about unintended consequences of biological solutions. In an attempt to save oak trees from gypsy moths, scientists released a parasitic European fly into the wild to feed on gypsy moths, but it also killed wild giant silk moths in huge numbers.
“We’re certain, through testing, that they will only eat the intended prey item, they won’t switch to other prey,” he says of the Ln Beetle.
Charles Bier is banking on its success. Standing on a small bridge over the stream at Bear Run, Bier considers why the eastern hemlock is so important to him.
“In winter, when all of the other trees are barren, there’s that iconic, everlasting hemlock tree,” he says. “It’s a very classic tree for the Appalachian mountains.”
Researchers say they can’t be certain, but Ln beetles appear to be containing the woolly adelgid in some areas, and gives them hope for the eastern hemlock.