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Goal: Deliver Benefits to the Public Managing hemlock woolly adelgids

Forest resource manager Jesse Webster (National Park Service) uses a beat sheet to sample for predators of the hemlock woolly adelgid (HWA). This sampling technique is highlighted in a new Forest Service guide that provides a strategy for integrating biological and chemical control of HWA. (Forest Service photo by Albert Mayfield)


Land managers aiming to protect hemlock trees and control hemlock woolly adelgids (HWA) have a new resource from the USDA Forest Service: a technology transfer publication with guidelines on integrating chemical and biological control of the invasive hemlock woolly adelgid.

The strategy for prolonging hemlock health includes limited use of insecticides combined with establishing HWA predators on untreated or previously-treated trees. Guidelines are provided for implementing, monitoring, and assessing the strategy.

Researchers are also evaluating the effectiveness of silvicultural treatments as well as biocontrol—insects that eat hemlock woolly adelgids.


A nonnative invasive insect, the hemlock woolly adelgid (HWA), threatens the ability of natural resource managers to maintain eastern and Carolina hemlocks as critical components of unique forest ecosystems in eastern North America. Although substantial progress has been made in both chemical and biological control of HWA, neither of these tactics applied alone is expected to provide adequate control of HWA throughout its introduced range.

A new USDA Forest Service resource manager’s guide titled “Integrating Chemical and Biological Control of the Hemlock Woolly Adelgid” presents a strategy for using biological and chemical control together in the same forest stands. The goal of the strategy is to prolong hemlock health on certain hemlock trees through temporary insecticide protection, while simultaneously establishing predators on nearby untreated trees.

Temporarily-protected hemlocks are expected to eventually support predators after their chemical treatment wears off. A separate research project showed that Laricobius nigrinus, a predatory beetle, significantly reduced populations of the winter generation of the hemlock woolly adelgid. However, this beetle inactive in the spring, suggesting the need for additional predators and control measures.

Another research project confirms that silvicultural treatments that allow more sunlight to shine on eastern hemlock trees can make them healthier, even if they are infested with hemlock woolly adelgids. Researchers are working to develop management recommendations, and plan to update the manager’s guide.

Webinar on the manager’s guide presented through Emerald Ash Borer University

Related article: To save the hemlock, scientists turn to genetics and natural predators - The Washington Post

Principal Investigators
Albert E. Mayfield III, Research Entomologist
Chelcy F. Miniat, Project Leader
4552 - Insects, Diseases, and Invasive Plants
4353 - Center for Forest Watershed Research
Strategic Program Area
Invasive Species
Integrating chemical and biological control of the hemlock woolly adelgid: a resource manager’s guide
Physiological responses of eastern hemlock (Tsuga canadensis) to light, adelgid infestation, and biological control: Implications for hemlock restoration
Impact of the introduced predator, Laricobius nigrinus, on ovisacs of the overwintering generation of hemlock woolly adelgid in the eastern United States
Rebound of Adelges tsugae spring generation following predation on overwintering generation ovisacs by the introduced predator Laricobius nigrinus in the eastern United States
CompassLive Articles
New Manager’s Guide for Controlling Hemlock Woolly Adelgids
Hemlock Woolly Adelgids & Their Predator Beetle, Laricobius nigrinus
Hemlock Seedlings Released from Shade
Research Partners
Noel F. Schneeberger - Forest Health and Economics, Eastern Region
Rusty Rhea - Forest Health Protection, Southern Region
David R. Zeitlow - NRS
Cindi Brown - Coweeta Hydrologic Laboratory, NRS
External Partners
Scott M. Salom - Virginia Tech, Department of Entomology
Kenton Sumpter - West Virginia Department of Environmental Protection
Tom McAvoy - Virginia Tech, Department of Entomology
Steven T. Brantley - Jones Center at Ichauway
Robert M. Jetton - North Carolina State University, Department of Forestry and Environmental Resources, Camcore