Imidacloprid is used to control the hemlock woolly adelgid in the eastern hemlock forests of the United States

The hemlock woolly adelgid (HWA), a native of Asia, a 1/32 inch long reddish purple insect that lives within its own protective coating, is a threat to eastern hemlock forests, and eastern and Carolina hemlock of all sizes are susceptible. The HWA came from Asia without any of the natural enemies that keep populations in check in its native range. HWA was first reported in the eastern US in Virginia in the mid 1950's. Since then, it has spread north to Connecticut and south through North Carolina. It reached eastern Tennessee in 2002, and was first reported in eastern Kentucky in spring 2006. Systemic insecticides containing the active ingredient imidacloprid can be used as soil drenches or injections to control the HWA.

Source:
Lee Townsend, Extension Entomologist and Lynne Rieske-Kinney, Associate Professor, Forest Entomologist
University of Kentucky College of Agriculture
http://www.ca.uky.edu/entomology/entfacts/ef452.asp