Northeast forest insects
| Authors: | Bradley P. Onken, Allison M. Kanoti, Dave Struble |
| Year: | 2012 |
| Type: | Book Chapter |
| Station: | Washington Office |
| Source: | Bechtold, William A.; Bohne, Michael J.; Conkling, Barbara L.; Friedman, Dana L.; Tkacz, Borys M., eds. 2012. A synthesis of evaluation monitoring projects by the forest health monitoring program (1998–2007). Gen. Tech. Rep. SRS-159. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 140 p. |
Abstract
The hemlock woolly adelgid (Adelges tsugae) ( HWA) is a serious nonnative pest of eastern (Tsuga canadensis) and Carolina hemlocks (T. caroliniana). The insect is currently found in 17 eastern States from southern Maine to northeastern Georgia and west to eastern Kentucky and Tennessee. On average, HWA spreads about 12.5 km per year, HWA dispersing naturally by wind and birds, and artificially on hemlock nursery stock. Infested nursery stock has resulted in isolated infestations in Michigan, Ohio, Vermont, New Hampshire, and Maine. Such isolated infestations are eradicated when possible. HWA feeds on stored nutrients in the ray parenchyma cells of the xylem by inserting its stylet bundle through the leaf cushion where needles attach to the twig. Abundant adelgids soon deplete nutrients vital to shoot growth the next growing season. Damage occurs over 4 to 10 years, and includes stunted shoot growth or no growth at all, graying needles, branch dieback, and eventually tree mortality. All ages of hemlock are susceptible from seedlings to mature trees. Other biotic and abiotic stress agents like the elongate hemlock scale (Fiorinia externa) and drought hasten tree decline. Extensive tree mortality has been reported throughout the infested region of the Eastern United States.