For at least a decade, the eastern hemlock trees in and around Nature Camp have been infested by the hemlock woolly adelgid (Aldeges tsugae), a true bug introduced into the eastern United States from Asia more than half a century ago. The telltale cottony white egg sacs along twigs are the adelgid’s unmistakable calling card—the insects themselves are extremely small and much less conspicuous—and are now familiar to an entire generation of Nature Campers. Adelgids feed on the sap of young hemlock shoots, and prolonged infestation often results in defoliation and leads to mortality. Although we have been fortunate to have lost very few trees within Nature Camp, the iconic hemlock near the Boys’ Bunkhouse has been in decline for several years, and the dense hemlock stands within the Big Mary’s Creek valley have been largely reduced to skeletal ghosts.
A number of treatment options have been employed to control hemlock woolly adelgid. The most commonly used chemical agent is imidacloprid, a systemic insecticide which is typically injected into the soil around the base of an infected tree. Other options include horticultural oils or insecticidal soaps. Last spring we developed tentative plans to treat a few trees in front of the Staff House with horticultural oil. If that treatment appeared effective, we would then expand the program by inviting members of the Nature Camp family to “sponsor” individual hemlock trees around Camp by donating funds to pay for the cost of treatment.
On the first day of Fourth Session last summer, the parent of a new camper approached me with the offer of his assistance in treating the hemlocks in Camp. Scott Salem is a professor of entomology at Virginia Tech who leads a research team investigating biological control of hemlock woolly adelgid. Over two days this winter Dr. Salem and lab specialist Tom McEvoy systematically treated several dozen hemlock trees around Nature Camp with imidacloprid, all of which had been donated by the manufacturer. They also released about 200 predatory beetles (Laricobius nigrinus), which feed on hemlock woolly adelgid in the western U.S. and which are related to a specialist predator in the adelgid’s native range in Japan. Raised in the lab from stock collected in the field, these beetles have been released on public lands throughout the East. Beetle larvae hatch in late winter and feed on adelgids throughout the spring, then burrow into the soil to pupate during the summer. Hence we won’t be able to observe any activity while Nature Camp is in session, but it will be interesting to monitor the health of our resident hemlock trees over the next several years. Thanks to Scott and Tom for their generous efforts to save such an important component of the forest around Camp.
For more information about this biological control program, see http://www.research.vt.edu/resmag/2007summer/bugs.html