Sustain Our Nation's Forests and Grasslands

Predator beetles released to control serious pest of hemlock trees

MAINE — Forest entomologists from the Maine Forest Service and U.S. Department of Agriculture Forest Service along with staff

Map showing the spread of hemlock woolly adelgid in 2016. A large swath of red shows counties infested before 2016; a larger swath of green shows the native range of hemlock. A few spots of yellow show counties infested since 2016.
This Forest Service map shows hemlock woolly adelgid infestations as of 2016. Forest Service map.

biologists from the Rachel Carson National Wildlife Refuge met in Kittery, Maine, to release predators of an invasive insect pest. The hemlock woolly adelgid, Adelges tsugae, is a serious pest of eastern and Carolina hemlock in the eastern United States.

A total of 500 predatory beetles, Laricobius osakensis (Lo), were released on the Rachel Carson National Wildlife Refuge to manage hemlock woolly adelgid populations. One thousand Lo were also released earlier this fall on Frye Island in Sebago Lake near Portland, Maine, augmenting a release of the same predator at the same site last season. Forest health specialists expect that the predator will establish at both sites in Maine and in time will serve as field insectaries from which collections of the Lo beetles can be made and moved to new sites in Maine.

Through the Forest Service’s National Hemlock Woolly Adelgid Initiative, more than 13,000 predatory beetles have been released so far this season across 10 states in the Northeast and Mid-Atlantic regions. Another 10,000 or more HWA predatory beetles have also been released by the Forest Service and state forest health specialists in the southern Appalachians. The national HWA Initiative was implemented in 2003 by the Forest Service’s Forest Health Protection program at the request of state agriculture and forestry officials to address the rising damage and increased spread of the insect. The main focus of the national initiative has been to develop and implement a biological control program to rear and release predators across the range of HWA.

The initiative is implemented by Forest Health Protection staff, state and university partners, and research scientists across the Northeastern Area and Southern Region. HWA is now established in all or parts of 20 eastern states (see map). Earlier this year the insect was also found to be established in three counties in southern Nova Scotia, Canada. We are collaborating with our Canadian colleagues in responding to HWA there, especially with regard to developing a biological control program.

Photo: Close-up of infested hemlock branch with pink ribbon tied around it. Clothes pins hold a bag of laricobious osakensis, predator beetles.
Laricobius osakensis, a predator beetle, is released on a hemlock infested with hemlock woolly adelgid. Forest Service photo.
Photo: Close-up of hand holding a hemlock branch infested with hemlock woolly adelgid.
Hemlock branch with hemlock woolly adelgid attached. Forest Service photo.
Photo: Close-up of hand holding a vial. Inside the vial are tiny predator beetles.
Vial of Laricobius osakensis to be released for control of hemlock woolly adelgid. Forest Service photo.