Texas Invasive Species InstituteAdelges tsugae
Hemlock Woolly Adelgid
Class: Insecta
Order: Hemiptera
Family: Adelgidae
Source: http://na.fs.fed.us/ Source: http://northgeorgia.edu/EnvironmentalLeadership
Description
Adelges tsugae is an aphid-like insect that is oval and blackish in color. Newly hatched nymphs (above right) are about the same size but reddish brown. What makes this minuscule insect conspicuous is that it produces a covering of wax filaments to protect itself and its eggs from natural enemies (above left).
Host Plants: Eastern Hemlock (Tsuga canadensis), Carolina hemlock (T. caroliniana), Western Hemlock (T. heterophylla) and mountain hemlock (T. mertensia).
Ecological Threat: In the eastern United States, eastern hemlock (Tsuga canadensis) is the dominant conifer because it is shade tolerant and long-living. Called the "redwood of the east," eastern hemlocks can grow more than 150 feet tall on trunks measuring six feet in diameter and can grow for hundreds of years. Hemlocks play a unique role in forest ecosystems creating habitats with characteristic soil chemistry and other ecosystem dynamics. Adelges tsugae feeds on the sap at the base of hemlock needles, disrupting nutrient flow and causing the needles to change from deep green to a grayish green, and then fall off. The loss of needles starves the tree to death, usually within three to five years of the initial attack. With Adelges tsugae annihilating the hemlocks it completely ruins to forest’s carbon balance, soil respiration rates and other habitat alterations that impact the forest wildlife.
Biology: The hemlock woolly adelgid is unusual in that it enters a period of dormancy during the hot summer months. The nymphs during this time period have a wax-filament cover that looks like wool. Feeding begins once the temperatures get cooler, around October and the adelgids continue to feed over the winter months.
The ovi-sacs of the winter generation contain up to 300 eggs, while the spring generation ovi-sacs contain between 20 and 75 eggs. When hatched, the first instar nymphs, called crawlers, search for feeding sites on the twigs at the base of hemlock needles and begin feeding on the young twig tissue and remain at that location throughout the remainder of their development. Unlike closely related insects that feed on nutrients in sap, the hemlock woolly adelgid feeds on stored starches which are critical to the tree’s growth and long-term survival.
Dispersal occurs primarily during the first instar crawler stage as a result of wind and by birds, and mammals that come in contact with the sticky ovi-sacs and crawlers. Long-distance movement of hemlock woolly Adelgid usually is a result of people transporting infested nursery stock.
History: Adelges tsugae was first identified off of the West Coast in 1924 and first reported off of the East Coast in 1951 in Richmond, VA. It may have been accidentally imported on tree nursery stock from Japan; and continues to spread to ornamental hemlocks through the nursery trade. However, early-stage larvae and eggs can be transported by mammals and birds moving through hemlock forests. By 2002, it was found in the Great Smoky Mountains National Park and by 2007 it was spreading at a rates ranging from 5miles /year to 10 miles /year and is found all throughout the Appalachian mountain range.
U.S. Habitat: Although in their native range, certain spruces are hosts during the sexually reproducing stages of the lifecycle. In the eastern United States, this Adelgid infests both Eastern Hemlock and Carolina Hemlock. Called the "redwood of the east," eastern hemlocks (Tsuga canadensis) can grow more than 150 feet tall on trunks measuring six feet in diameter. In the West, it feeds on Western and Mountain Hemlock but both of those trees are more resistant than the eastern and Carolina species.
Distribution
Native Origin: East Asia
U.S. Present: CA, CT, DE, GA, KY, MD, ME, NC, NH, NY, OR, PA, RI, SC, TN, VA, VT and WV
Management
The best time to effectively manage this pest is late September through October. Registered insecticides applied according to label directions during this period target overwintering females. A mid- to late June spray may help reduce the number of developing nymphs. Moving bird feeders away from hemlocks and removing isolated infested trees from a woodlot can help prevent further infestations. State quarantines help prevent the movement of infested materials into non-infested areas.
There are several types of chemical control options that can be applied to the leaves directly (foliar), systemically by being injected as a solid or drenched as a liquid into the ground. The foliar application method is preferred by nursery owners and growers. Taking this preference into account, studies have performed insecticide application comparisons and have shown that foliar application of an insecticide provides season-long hemlock protection and actually kills off Adelges tsugae during their adult emergence. These studies have also shown that systemic insecticides can also be applied to the leaves of hemlocks and provide effective yearlong treatment. Chemical treatments offer a short-term solution, and applications may need to be repeated in subsequent years.
In 2011 the USDA created a control plan for Adelges tsugae. For more information, click here.
Text References
Internet Sources
http://www.saveourhemlocks.org/adelgid.shtml
http://www.nps.gov/grsm/naturescience/hemlock-woolly-adelgid.htm
http://ento.psu.edu/extension/factsheets/hemlock-woolly-adelgid
http://www.dontmovefirewood.org/gallery-of-pests/hemlock-woolly-adelgid.html
