You are here: Home / Research Topics / Research Highlights / Individual Highlight

Research Highlights

Individual Highlight

First Release of a New Biological Control of Hemlock Woolly Adelgid

Photo of Vial of silver flies ready for field release. USDA Forest ServiceVial of silver flies ready for field release. USDA Forest ServiceSnapshot : Forest Service scientists and their research partners tested and released two species of silver flies from the western United States for biological control of hemlock woolly adelgid in Tennessee and New York.

Principal Investigators(s) :
Havill, Nathan P.  
Research Station : Northern Research Station (NRS)
Year : 2015
Highlight ID : 860


Hemlocks are important trees in watersheds and in the urban landscape. Since the 1980s the hemlock woolly adelgid (HWA) has been killing hemlock trees in the eastern United States. HWA was introduced to the eastern U.S. from Japan, but genetic research by Forest Service scientists discovered that a separate, native group of hemlock adelgids exists in the western U.S. and Canada. These western adelgids have a natural community of predators that are lacking in the East. Two species of silver fly that feed on western adelgids have undergone years of laboratory evaluation to determine if they would be safe to release in the East. This year, these western silver flies were released for the first time in New York and Tennessee by Forest Service scientists, with the help of state and university collaborators. Some of the flies were released into mesh bags enclosing hemlock branches, so they could be observed more closely. These were found to successfully feed and reproduce. Researchers will continue to monitor the release sites for fly establishment and impact on HWA in the hopes that they will help reduce HWA populations.

Forest Service Partners

External Partners

  • Albert Mayfield, SRS
  • Kimberly Wallin, NRS
  • Darrell Ross, Oregon State University
  • Mark Whitmore, Cornell University
  • Stephen Gaimari, California Department of Food and Agriculture

Program Areas