Extension agents across much of the United States often get questions from homeowners and forest managers about the forest tent caterpillar (Malacosoma disstria), and their concerns are understandable. The native pest can cause significant defoliation of a variety of host trees, and they have a habit of forming their cocoons—in great abundance—on tree trunks and walls.
The good news is that M. disstria is not an economically impactful pest, and it can often be effectively managed with non-chemical controls. Insights on the forest tent caterpillar’s life cycle, behaviors, and management methods are profiled in a new guide in the open-access Journal of Integrated Pest Management.
Timothy D. Schowalter, Ph.D., author of the JIPM profile, has studied the forest tent caterpillar during time at Oregon State University and now with the Louisiana State University Agricultural Center. “It is relatively unique among forest-related insects in having a highly visible urban presence that makes it a nuisance among a larger human population than typical of forest ‘pests,'” he says.
M. disstria larvae emerge between April in the southern U.S. and July in the north, and they feed on host-tree foliage for four to seven weeks as they develop through five to eight instars. “Southern populations prefer water oak and sweetgum and do poorly on sugar maple and aspen, whereas northern populations prefer sugar maple and aspen and do poorly on water oak and sweetgum,” Schowalter says.
Forest tent caterpillars—which get their common name from the silk mats in which they rest amid feeding on foliage—can cause severe defoliation, but only rarely does that lead to tree death. Rather, their effects can be more indirect, such as altering forest dynamics; Schowalter notes one study that found overstory defoliation after a forest tent caterpillar outbreak promoted understory growth, shifting the a mainly aspen forest toward more conifer dominance. Where forest tent caterpillars intersect with human environments, they can become a nuisance pest, defoliating ornamental trees and forming cocoons on buildings, for instance.
Schowalter recommends mechanical methods for managing forest tent caterpillar, as well as some biopesticides, if necessary. Tactics include:
- Removing egg masses from trees (especially during winter when they’re easier to find).
- Sweeping larvae and pupae from walls and trees with a stiff broom or pressure washer.
- Adhesive bands on tree trunks to capture larvae crawling up or down trees.
- Microbial insecticides including Bacillus thuringiensis, spinosad, and baculovirus, all of which can be applied with minimal effect on nontarget insects.
Further research on M. disstria might explore glycosides, which several host trees produce as a defense mechanism. “Foliage glycosides are particularly effective feeding deterrents and reduce survival [of forest tent caterpillar],” Schowalter says. “Some of these phytochemicals might be added to a list of biorational control methods.”
Journal of Integrated Pest Management