Hemlock Woolly Adelgid

Adelges tsugae, the hemlock woolly adelgid, is a serious pest of Eastern hemlock in the northeastern states. This insect was first reported in southeastern Pennsylvania in the late 1960s and has spread to both ornamental and forest hemlocks. Adelgids are small, soft-bodied insects that are closely related to aphids. The hemlock woolly adelgid sucks sap from the young branches which results in premature needle drop and branch dieback.

These insects display several different forms during their life cycle, including winged and wingless adults. The females are oval, blackish-gray, and about 1 mm in length. Newly hatched nymphs called "crawlers" are approximately the same size, reddish-brown, and produce white, waxy, cottony or wool-like tufts that cover their bodies throughout their life. The white-woolly masses are 3 mm or more in diameter. The presence of these woolly flecks on twigs and at the base of the hemlock needles is the most obvious indicator of an infestation.

For more background information download the booklet Biology and Control of Hemlock Woolly Adelgid published by the USFS-Forest Health Technology Enterprise Team. A shorter summary is available on our Forest Health Fact Sheet on Hemlock Woolly Adelgid or  the U.S.Forest Service Pest Alert for Hemlock Woolly Adelgid.

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