Winter Moths (and caterpillars) are quickly spreading in Massachusetts!

The Winter Moth (Operophtera brumata  (L.))

Insect Order: Lepidoptera

Family: Geometridae

Origin: Winter moth is an insect pest that was introduced to North America from

Europe. Its introduction has been known for years in various regions of eastern Canada,

including: Nova Scotia, Prince Edward Island, and parts of New Brunswick. It has also

been a pest in the northwestern region of North America, namely Vancouver, British

Columbia. Winter Moth was introduced into the United States and has warranted control

measures in Washington and Oregon. It is also a problem in the United Kingdom

(England and Scotland).

This pest is now in Massachusetts in  coastal areas from the North Shore, down

around Boston, through Plymouth County, South Shore and out onto Cape Cod as far as

Chatham (approximately mid-Cape).  It is the first known occurrence of it in outbreak

proportions in New England.

Injury and Host Plants: Many different deciduous plants are susceptible. These include:

oaks, maples, basswood, ash, crabapples, apple, blueberry, and certain spruces such as

Sitka spruce (Scotland).  Young larvae (caterpillars) are tiny inchworms and they tunnel

into buds where they feed. They especially seem to prefer fruit trees such as apple,

blueberry, and cherry, and crabapple.  However, they also tunnel into the buds of maples.

These caterpillars move from bud to bud as they feed. Delayed bud opening due to cool

weather conditions can lead to bud death as  the caterpillars have longer time to feed.

Older larvae feed in the expanding leaf clusters and are capable of creating defoliation in

high populations.  Research in Canada has shown that four consecutive years of partial

defoliation of deciduous hosts can lead to branch mortality while complete defoliation in

each of those years leads to tree mortality.  In certain regions of Nova Scotia, this pest is

responsible for a 40% red oak mortality in forested stands.

Life Cycle:  Moths (the adult stage) of the winter moth emerge from the soil usually in

late November and can be active into January. The adults are strongly attracted to lights

and can often be found flying around outside lamps or holiday lights. The male moths are

small, light brown to tan in color and have four wings that are fringed with small elongate

scales that give the hind margins a hairy or fringed appearance.  The female is gray,

wingless and, therefore, cannot fly.  She emits a sex pheromone or scent that often

attracts clouds of male moths.  Females are usually found at the base of trees but can be

found almost anywhere.  After mating, the female deposits an egg cluster on tree trunks

and branches, in bark crevices, under bark scales, under loose lichen, or elsewhere. The

adult moths then die and the eggs over-winter.  Eggs hatch when temperatures average

around 55

It is believed that egg hatch in Massachusetts occurs when 20 – 50

Growing Degree Days (base 50) have accumulated.  This means that egg-hatch usually

occurs in the spring, before bud break of most of its host plants. Newly hatched larvae

often crawl up tree trunks and produce a long silken strand of silk which makes them air

buoyant.  This larval dispersal method is known as “ballooning”. In certain situations,

winter moth caterpillars can arrive in areas where they are not expected to be a problem,

given topography and wind patterns.