Native to Asia, it was first reported in western North America in 1924 and in eastern North America in 1951. Populations found in the eastern United States originated from southern Japan. In their native range they cause little damaged to the hemlock trees they feed on, most likely due to natural enemies and host plant resistance.
Hemlock Wooly Adelgids are related to aphids and are in the family Adelgidae. They are less than 1/16-inch (1.5-mm) long. Hemlock Wooly Adelgid vary from dark reddish-brown to purplish-black in color but as they mature they produce a covering of wool-like wax filaments to protect themselves and their eggs from natural enemies and prevent themselves from drying out. Their wool is most obvious when the adelgid is mature and laying eggs. Hemlock Wooly Adelgid are female and produce young through asexual reproduction. They go through a period of dormancy in the summer.
In North America they feed on all types of hemlock but eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana) are the most vulnerable. They use their long mouthparts to feed on the sap from the hemlock foliage. This causes the Hemlock’s needles to discolor and drop prematurely, reducing the tree’s growth while the loss of new shoots and needles impairs the tree’s health. Infestations can be fatal to the tree three to ten years, depending on climate and other factors such as stress and disease.
Hemlock Wooly Adelgid is moved by wind, birds, wildlife and through humans moving infected materials such as nursery stock. Moving bird feeders away from hemlocks and removing isolated infested trees from a woodlot can help prevent further infestations. Systemic insecticides can be effective on large trees when applied to the soil around the base of the tree or injected directly into the stem, but this is not possible when large amounts of trees are infected or in sensitive areas and is only a short-term solution. Biological control using predators of the Hemlock Wooly Adelgid from its native range are being researched.
It is found from Georgia to Maine and Westward to kentucky and Tennessee. It is established in sixteen states.
Photo of Hemlock Woolly Adelgid on hemlock: Conneticut Agricultural Experiment Station Archives, Conn. AES.
(From: http://na.fs.fed.us/spfo/pubs/pest_al/hemlock/hwa05.htm and http://www.dec.ny.gov/animals/6986.html and http://www.saveourhemlocks.org/)
