Biological Control Released At Martha Sundquist State Forest To Protect Hemlocks

Wednesday, December 5, 2012

Predatory beetles that feed on hemlock woolly adelgids (HWA), an invasive pest killing swaths of hemlock trees from eastern Tennessee to the Cumberland Mountains, were released Tuesday at Martha Sundquist State Forest in Cocke County. The release was an effort by the Tennessee Department of Agriculture Division of Forestry (TDF) to protect young eastern hemlock seedlings from the invasive exotic pest, which is responsible for killing many, if not most, of the mature hemlocks in the state forest.

“Martha Sundquist State Forest is a good site for these beetles to be released because there is a healthy population of HWA to sustain them,” said Douglas Godbee, TDF Forest Health Forester. “We will monitor these beetles over the next couple of years in hopes that they will reproduce, become an established population, and continue to prey on HWA in order to eventually control the HWA population.”

Native to Asia, the hemlock woolly adelgid (Adelges tsugae) is a small, aphid-like insect that threatens the health and sustainability of eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana) in the Eastern United States. It feeds at the base of the needles and can quickly populate all needles of a tree, sucking the sap and ultimately causing mortality within 3 to 10 years of infestation. The potential ecological impacts of this exotic pest are comparable to that of Dutch elm disease and chestnut blight. HWA was first reported in the U.S. in 1951 near Richmond, Va., and has since spread to 17 states, from Maine to Georgia. 

The predatory beetles, Laricobius nigrinus, are especially good at controlling HWA because its lifecycle syncs with HWA’s lifecycle, as the larvae feed exclusively on HWA eggs and can only complete their development on HWA eggs. They were reared by the University of Tennessee Institute of Agriculture at the Lindsay Young Beneficial Insects Laboratory.

Since its detection in Tennessee in 2002, HWA has spread to 35 counties in East Tennessee and the Cumberland Plateau. On average, HWA has been spreading from east to west at roughly 15 to 20 miles per year. It is estimated to have been in Martha Sundquist State Forest since 2005.

“Martha Sundquist State Forest has a healthy population of younger hemlock trees but if left untreated, these trees will eventually become infested and die,” said Mr. Godbee.

HWA is spreading rapidly by storm winds and migratory birds, as well as “hitchhiking” on mammals and humans. Infested nursery stock can also transport the insect into new areas. Hemlock is not a highly valued timber species but provides invaluable ecological benefits to the forest such as habitat, stream temperature regulation, and stream bank stability. Loss of these benefits not only disrupts the delicate natural systems in the forest but also affect aesthetic and recreational benefits.

Agencies across Tennessee have joined together in the fight against the hemlock woolly adelgid and formed The Tennessee Hemlock Conservation Partnership. The group works to track the rate of spread of HWA across the state, collaborate on HWA treatment projects on public land, and educate the public about HWA. More information can be found at or contact the Division of Forestry, Forest Health at 615 837-5432

For more information about other programs and services of the Tennessee Department of Agriculture visit

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