“Winter? Moth”

Contact: Bob Tatman, Maryland Department of Agriculture | TatmanRL@mda.state.md.us

“Winter? Moth”
Photo: USDA Forest Service

ANNAPOLIS, MD (October 4, 2010) – Winter moth (Operophtera brumata), an exotic pest from Europe, has the potential to be a very serious problem in deciduous forests throughout the eastern United States. It already is well established in Nova Scotia, eastern Massachusetts, British Columbia, Oregon and Washington states. Winter moth is a more general feeder than the gypsy moth, which prefers to feed on oaks and hickories. Winter moth does not experience population collapses outside its native range, so several consecutive years of defoliation do occur. Because of its ability to feed on a large range of hosts and potential to have many consecutive years of defoliation, MISC has declared winter moth to be the October Invader of the Month.

Adult female winter moths are gray and wingless. The adult males are light brown and small. Females are flightless and attract males with a pheromone. Adult males are also attracted to lights. The adults emerge in late November and December in Massachusetts. Larvae are light green loopers that measure one inch when fully grown. The adults mate in winter, females lay their eggs on tree bark crevices, branches, etc. Eggs hatch in the spring when temperatures average 55 degrees Fahrenheit. After hatching, the larvae crawl up tree trunks and produce silken threads that catch the wind and carry the larvae to new hosts. This natural dispersal method is called ballooning. Young larvae feed within buds and on expanding foliage, while older larvae consume leaves. Feeding is completed by mid-June when larvae pupate in the soil. Pupae remain in the soil until the adults emerge the following winter.

Winter moth is found in deciduous forests and on residential deciduous trees. They feed on oaks, maples, basswood, ash, crabapple, apple, blueberry, and certain spruces. They apparently cannot survive in winter hardiness zone 5a (-20 to -15 degrees Fahrenheit). Maryland's hardiness zones are 6a, 6b and 7a.

Winter moth was introduced to North America from Europe and was first reported in Nova Scotia in the early 1930s. Winter moth has the potential to be a multi-year, early spring defoliator of a broad list of deciduous trees and shrubs. This could result in large areas of tree mortality. They may even cause tree mortality where gypsy moth has already reduced the oak population. Winter moth was discovered in eastern Massachusetts in 2002. Significant defoliation has occurred each year since then. Initially, winter moth spread slowly, but in 2009 it spread very quickly (approx. 30+ miles) and now exists as far west as western New Hampshire; Gardiner, Massachusetts; and Staten Island, New York. It is this recent rapid expansion that is causing increased concern. Also, surveys indicate that in the infested areas, populations have increased considerably.

Since winter moth is very similar to the native spring and fall cankerworm, it will be difficult to determine its presence/absence from Maryland. There is a pheromone that can be used to monitor for winter moth but Bruce spanworm (Operophtera bruceata) is very similar and can only be distinguished by sophisticated analysis. If winter moth should become established in Maryland, the best hope is to release and establish Cyzenis albicans, a parasitic fly that specializes on winter moth and is thought to be the agent primarily responsible for the decline of winter moth densities in Canada. If effective biological control does not exist and defoliation occurs, an application of a registered pesticide may be warranted.

For more information, please visit:

UMass Extension Fact Sheet
Massachusetts DCR Pest Alert
For more information about Invasive Species of Concern in Maryland, visit www.mdinvasives.org

photos available electronically on request.