This story was first published on April 20, 2018
12/18/20 Update: The Western Pennsylvania Conservancy has an insectary not only at Bear Run but also at Wolf Creek Narrows Natural Area in Butler County. The Conservancy is considering establishing one at its Bennett Branch Forest property in Elk and Clearfield counties.
At the Bear Run site, the Conservancy will check back this spring to see if the hemlock woolly adelgids introduced last year have spread. Once the adelgids have colonized there, the beetles can be released into the insectary. It could take up to 2 years.
“An insectary is basically a nursery habitat where you grow insects,” he explained.
LISTEN: Could These Tiny Beetles Save PA’s Hemlocks?
Bier pointed 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 look a little sparse.
“You can see right there, that’s definitely hemlock woolly adelgid,” he said, as he pointed to the underside of a branch.
Hemlock wooly adelgids 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 explained.
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, director of land stewardship for the Western Pennsylvania Conservancy, said around 2009, adelgids 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 made it here to Bear Run Reserve,” he said.
There is an insecticide that helps control adelgids, but Zadnik said it has 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 said.
Enter the “Insectary”
Across a parking lot, through tall dry grass stand small shrubs protected by an orange deer fence.
“Twelve little hemlocks,” Zadnik laughed.
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 said.
Is it really a good idea to release a non-native beetle into the forest?
Mark Whitmore, forest entomologist from Cornell University, has been working with the USDA on regulations for releasing Ln Beetles to prey on adelgids. He said 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 the fly 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 said of the Ln beetle.
Charles Bier is banking on the beetle’s success. As he stood on a small bridge over a stream at Bear Run, Bier considered 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 said. “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.