Bradford Woods Borough News

Posted on: June 2, 2017

Be Aware: Hemlock Woolly Adelgid

Please contact a professional when suspicious of a woolly adelgid presence on your hemlocks for detection and treatment. Also, please contact neighbors or other residents about the adelgid to create awareness of the pest. Early detection is helpful in treatment. Please see below for more information or click here for multiple articles found online.


Hemlock woolly adelgid (Adelges tsugae), or HWA, is member of the Sternorrhyncha suborder of the Order Hemiptera and native to East Asia. It feeds by sucking sap from hemlock and spruce trees (Tsuga spp.; Picea spp.). In eastern North America, it is a destructive pest that gravely threatens the eastern hemlock (Tsuga canadensis) and the Carolina hemlock (Tsuga caroliniana). Though the range of eastern hemlock extends north of the current range of the adelgid, it could spread to infect these northern areas as well. Accidentally introduced to North America from Japan, HWA was first found in the eastern United States near Richmond, Virginia, in the early 1950s. The pest has now been established in eighteen eastern states from Georgia[1] to Massachusetts, causing widespread mortality of hemlock trees. As of 2015, 90% of the geographic range of eastern hemlock in North America has been impacted by HWA.


An adult individual averages a body length of 0.8 mm and is oval in shape.[3]  The tiny brown-colored insect has four thread-like stylets that are bundled together and function as a mouthpart.  Three times the length of its body, the stylet bundle pierces the host plant’s  parenchymatic ray tissue to derive nutrition from stored reserves.[4] It may also inject a toxin while feeding.[5] The resulting desiccation causes the tree to lose needles and not produce new growth. Hemlocks stricken by HWA frequently become grayish-green rather than a healthy dark green. In the northern portion of the hemlock’s range, death typically occurs four to ten years after infestation. Trees that survive the direct effects of the infection are usually weakened and may die from secondary causes.[6]

The presence of HWA can be identified by its egg sacs, which resemble small tufts of cotton clinging to the underside of hemlock branches. In North America, the hemlock woolly adelgid asexually reproduces and can have two generations per year. Both generations are parthenogenetic and exclusively female.[3] In its native Asian habitat is a third winged generation called Sexupera; this generation’s sexual reproduction requires a species of spruce that is not found in the Eastern United States and therefore dies. Between 100 and 300 eggs are laid by each individual in the woolly egg sacs beneath the branches. Larvae emerge in spring and can spread on their own or with the assistance of wind, birds and/or mammals. In the nymph stage, the adelgid is immobile and settles on a single tree

FIGURE 1.—Hemlock woolly adelgid ovisacs.FIGURE 2.—Hemlock woolly adelgid nymphs in dormancy.Image result for hemlock woolly adelgidImage result for hemlock woolly adelgid

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