The hemlock woolly adelgid, an invasive aphid-like insect native to Japan was originally introduced to the Western United States in the 1920s. It was first discovered in the eastern United States in 1951 near Richmond, Virginia, and is now reported in 18 states including New York.
HWA is a sap feeder that inserts its mouth into the hemlock tree and remains there for the rest of its life feeding on the stored starches of the tree. Usually, the trees die within four to 10 years. Although all species of hemlock are vulnerable to attack, severe damage occurs in eastern hemlock trees.
Staff from the New York State Hemlock Initiative, in cooperation with DEC’s Invasive Species and Ecosystem Health program, recently released 856 little black beetles in a stand of hemlocks harboring HWA in Greene County. Over 10,000 Laricobius nigrinus beetles have been released across New York State this season. Laricobius beetles are specialist predators to HWA. The biological-control effort isn’t expected to eradicate the infestation, but it should reduce the HWA populations.
USDA Forest Service research entomologist Bud Mayfield, who conducted a study on the effect of beetles on the HWA population, said:
Every fall and winter, the Laricobius beetles chow down on the HWA egg clusters or ovisacs. They also eat adult adelgids. And the beetles lay their eggs in the adelgid egg sacks, so the beetle larvae also eat the adelgids. The beetles can destroy or disturb 80 percent of egg clusters, drastically diminishing the size of the winter sistens generation.
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