A species of silver fly, an instrument for controlling the invasive aphid-like insect hemlock wooly adelgid (HWA), has established itself in upstate New York, the Department of Environmental Conservation has announced.
The Cornell University-based New York State Hemlock Initiative (NYHI), which has been importing the bugs from the Pacific Northwest and raising them in its laboratory for nearly a decade, confirmed that a self-sustaining population has been documented in the Finger Lakes area.
Once established, a silver fly population will expand and spread beyond the original point of introduction, becoming part of a permanent, biological check on Hemlock Wooly Adelgid, which was first encountered on Lake George in 2017.
According to Dr. Mark Whitmore, the director of the NYHI, the discovery of a self-sustaining population of the species of silver fly, Leucotaraxis argenticollis “is huge news, offering hope for the effective biological control of HWA in the Lake George basin” and other parts of the Adirondacks where the invasive pest has been found, such as the Champlain Valley and Great Sacandaga Lake.
“Introducing a predator from another area, importing it to one where the targeted pest is enemy-free, is classic biological control,” said Whitmore. “Establishing a population of predators is one of the most difficult steps in the process, but also the most important.”
The discovery of an established silver fly population “marks an important step forward in HWA control and hemlock conservation,” the DEC stated.
If a population of silver flies has established itself in the Finger Lakes area, it is safe to say that others are now colonizing other areas of the state, where the NYHI and the DEC also released silver flies, said Whitmore.
“We just need to look for them, which is what we will be doing,” said Whitmore.
Whitmore said a recent experiment by a team of entomologists found that Leucotaraxis argenticollis, the species that established itself in the Finger Lakes, can survive winters in the coldest parts of New York State.
Researchers are focusing their attention not only on silver flies but on a beetle, also from the Pacific Northwest.
According to the DEC, beetles feed on adolescent and adult HWA during the fall and winter while the silver flies prey on the aphid’s eggs in the spring. According to the DEC, the unleashing of the silver flies “complements the release of the beetles.”
“The goal of these deployments of predatory insects is to establish stable populations in the area and provide long-term, year-round protection for the region’s hemlock forests,” the DEC stated.
According to the DEC, “beetles have been thriving, with established populations at 18 release sites and documented long-distance dispersal in the Finger Lakes, Lower Hudson, and Catskills regions. The success of the beetles suggests that silver flies may also be able to take hold and contribute to long-term biological control.”
Members of the Lake George Hemlock Coalition, established in 2024 to treat infected trees, prevent future infestations and identify priority stands, also welcomed reports that a silver fly population has established itself in New York State.
“A repopulating insect that will suppress the invasive is the holy grail of bio-controls,” said Dave Wick, executive director of the Lake George Park Commission. “Developing bio-controls has always been the goal.”
“Bio-controls offer long-term hope that we can maintain healthy hemlock forests here at Lake George, where they can continue deliver water quality for streams, habitat for birds and animals and scenic beauty,” said Mike Horn, executive director of the Lake George Land Conservancy. “These trees define our forests.”
According to Horn, HWA was discovered in 2023 at the LGLC’s Clark Hollow Bay Preserve on northern Lake George, where both beetles and silver flies have been released.
“We’re very excited,” said Horn. “We hope the natural predators establish themselves and create a long-term, cyclical, predator-prey balance.”
Over the past year, the Hemlock Institute has released more than 45,000 insects naturally engineered to prey on HWA and will continue to monitor their progress in establishing themselves throughout the state, the institute stated in a press release.
Until the natural predators establish themselves, the most effective method of controlling HWA remains insecticides, the Lake George Hemlock Coalition states. According to the DEC, two different insecticides, one fast-acting, killing the insect before it can reproduce, the other affording the tree long-term protection, are applied to bark near the base of the tree and absorbed through its tissue. When HWA attaches itself to the tree to feed, it receives a dose of the pesticide and is killed.
