Hemlock woolly adelgid infestation on eastern hemlock.
Photographer: Connecticut Agricultural Research Station, Bugwood.orgThe hemlock woolly adelgid, Adelges tsugae (HWA), arrived by accident to the eastern United States in the mid-1900s. By the late 1980s, this little sap-sucking insect began killing entire forests of eastern hemlock trees. There are currently no practical and safe treatments for preventing infestation of large stands of eastern hemlock by HWA.

For more information: https://www.nrs.fs.fed.us/disturbance/invasive_species/hwa/