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The hemlock woolly adelgid is an aphid-like invasive species from Asia that kills hemlock trees over a period of years by feasting on starch reserves crucial to the trees’ survival. The adelgids were first spotted in Richmond, Virginia, in 1951, and by 2005 had infested half of all hemlock groves between Maine and Georgia.
Hemlocks in the Northeast are now under threat.
UVM research assistant professor Kimberly Wallin and Oregon State’s Darrell Ross have identified two species of silver flies that prey on the adelgids. The scientists hope to determine whether the flies will be an effective predator for the pests.
“This is the first time this has been done with these flies; it’s a brand-new idea. We’re hopeful,” Wallin said in a news release.
Wallin and Ross have successfully bred and released test groups of the West Coast silver flies into forests in New York and Tennessee. Those flies have been breeding, laying eggs and hunting adelgids successfully.
“These flies are the most promising lead in a long time,” Wallin said.
The invasive adelgids have few natural predators to check their population growth. According to the release, the East Coast has its own native species of silver fly that preys on adelgids in pine trees, but not those infesting hemlocks.
“Populations of flies in the West search for hemlock trees, and that’s where they find their hosts,” Ross said. “The same species in the East has evolved to look for pine trees. They probably use chemical cues from those trees to find their habitat and their hosts. That’s why it’s useful to take the flies from out here, because they’ll look for hemlock trees and feed on the hemlock woolly adelgid in the East.”
Ross said it will take time to determine whether the silver fly will affect the numbers of adelgid. Wallin said they hoped that the flies could at least check the adelgids’ population growth long enough to give the hemlock trees time to recover.
“Once hemlock is removed, the soil type changes, the stream dynamics change, the forest type changes — and it’s hard to recover,” Wallin said. “We need to try to do something to protect these trees.”