Adelges tsugae, the hemlock woolly adelgid (/əˈdɛl.dʒɪd/) or HWA, is an insect of the order Hemiptera (true bugs) native to East Asia. It feeds by sucking sap from hemlock and spruce trees (Tsuga spp.; Picea spp.). In its native range, HWA is not a serious pest because populations are managed by natural predators and parasitoids and by host resistance. In eastern North America it is a destructive pest that threatens the eastern hemlock (Tsuga canadensis) and the Carolina hemlock (Tsuga caroliniana). HWA is also found in western North America, where it has likely been present for thousands of years. In western North America, it primarily attacks western hemlock (Tsuga heterophylla) and has only caused minor damage due to natural predators and host resistance. Accidentally introduced to North America from Japan, HWA was first found in the eastern United States near Richmond, Virginia, in 1951. The pest is now found from northern Georgia to coastal Maine and southwestern Nova Scotia as well as areas of western Michigan near the eastern Lake Michigan shoreline. As of 2015, HWA has affected 90% of the geographic range of eastern hemlock in North America.
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Hemlock woolly adelgid in the context of Thain Family Forest
The Thain Family Forest is a 50-acre (20 ha) section of old-growth forest along the Bronx River in the New York Botanical Garden, for a time known as the Native Forest and historically as the Hemlock Grove. Its heritage dates in part to pre-colonial Lenapehoking. New York City acquired 4,000 acres (~1620 ha) as parkland in 1888, and in 1895 the New York Botanical Garden site was chosen here primarily due to the presence of the forest, which covers about one-fifth of the garden grounds. Founding director Nathaniel Lord Britton described the site as "the most precious natural possession of the city of New York". The canopy is in various zones such as oak, hemlock, beech, sweet gum and mixed. The eastern hemlock, the forest's original namesake, declined in the early 20th century, due to the hemlock woolly adelgid and the elongate hemlock scale. Its 2011 redevelopment was supported by John Thain and Carmen Thain, and included the removal of non-native species as well as the expansion of native ones. Several walking trails traverse the forest. Appointed in 2021, Eliot Nagele serves as the director of the Thain Family Forest.
Hemlock woolly adelgid in the context of Tsuga canadensis
Tsuga canadensis, also known as eastern hemlock, eastern hemlock-spruce, or Canadian hemlock, and in the French-speaking regions of Canada as pruche du Canada, is a coniferous tree native to eastern North America. It is the state tree of Pennsylvania. Eastern hemlocks are widespread throughout much of the Great Lakes region, the Appalachian Mountains, the Northeastern United States, and Maritime Canada. They have been introduced in the United Kingdom and mainland Europe, where they are used as ornamental trees.
Eastern hemlock populations in North America are threatened in much of their range by the spread of the invasive Hemlock woolly adelgid, which infests and eventually kills trees. Declines in population from hemlock wooly adelgid infestation have led to Tsuga canadensis being listed as Near Threatened on the IUCN Red List.