Winter moths ascend on Vineyard once again

By Aubrey Gibavic - December 14, 2006

With one light snow dusting behind us, tiny white flakes floating down from above may not be much of a surprise. But if the flurries appear in the next few weeks, look closely, because they may not be what they seem.

Martha's Vineyard is in the midst of winter moth season, and Islanders have started to notice the cloudy white insects swarming around porch lights and holiday decorations, and at the base of various species of trees.

According to a report produced by University of Massachusetts Amherst Extension experts, (umassgreeninfo.org), "Massachusetts still appears to have the largest and most damaging populations of this pest."

Tree wardens in many Island towns acknowledge that the winter moth - and its spring caterpillar counterpart - is a problem, but say they have few resources to control the pests.

The winter moth is the adult form of the pesky green caterpillars that infest the Island in the spring and defoliate thousands of acres of land. The moth was first introduced to North America in 1949 via Nova Scotia, but was only detected in Massachusetts in 2003. No one is quite sure how the winter moths gained a foothold in Massachusetts, but the highest populations are found on Cape Cod and in Plymouth and Essex counties.

Male moths, which are light brown in color and appear hairy due to scales on their wings, are attracted to light and are often seen hovering around outdoor lamps or holiday decorations. Residents Island-wide have reported seeing clouds of them swarming even vehicle headlights.

The female moths are gray, nearly wingless, and cannot fly. Instead they cluster near the base of trees and emit a sex pheromone that attracts clouds of male moths.

After mating, which occurs around this time each year, the female moth deposits her egg clusters, usually in a crevice of a tree or other hidden, protected place. But last year, Islanders even spotted the dark green eggs - which look like small mud splatters - on decks, windows and glass doors.

The adult moths then die, and the eggs stay put until a string of temperate days, usually in March or April on Martha's Vineyard, when the one-inch caterpillars hatch. They feed voraciously until late June, defoliating shade and fruit trees, and shrubs, and then drop into the ground to pupate. The process starts all over again when the moths emerge from the soil around Thanksgiving.

Winter moth caterpillars defoliated approximately 21,000 acres of land in Massachusetts last year, according to UMass Extension experts. In addition, almost 250,000 acres of land was defoliated by gypsy moths working in concert with forest tent caterpillars.

Researchers from UMass and the Massachusetts Department of Conservation and Recreation are in their second year of tracking the winter moth, by way of "trunk banding." The data collected shows that there were between 1,000-2,000 female moths per tree. Each female produces up to 150 eggs, which translates to at least 150,000 eggs per tree.

Controlling the outbreak

The UMass Extension report outlines various techniques for controlling the winter moth population. Since a natural predator does not exist, various forms of natural controls, such as parasites like flies and wasps, have been introduced in other areas.

"However, two years of research in Massachusetts has shown that our naturally occurring predators are not yet, at least, having much of an impact on winter moth populations," the report states.

In May of 2005, an initial release of cyzenis - a fly that attacks winter moths - was performed in Plymouth County. With previous success on the west coast, Dr. Joseph Elkinton and his lab group at UMass are performing the trials in other parts of Massachusetts. Several thousand cyzenis are expected to be released this year.

"Tree banding" is the name given to the method of attaching sticky paper or plastic to the base of a tree, in order to trap the female moths. The study states that in peak population years, the bands have been known to fill up with moths in one hour.

"In some cases, it has been witnessed that female moths, upon approaching the barriers, lay their eggs on the tree trunks just below or above the barriers," the report reads. Researchers are also concerned about the toxic sticky substance, and worry that if it is installed improperly, the tree could be harmed.

Dormant oil sprays, insecticidal soap, and chemical insecticides are just a few of the other methods introduced to control the winter moth infestation, along with a variety of name brand insecticides.

Tisbury Department of Public Works director Fred LaPiana said his department drafted a warrant article for the special town meeting that was scheduled for December, which would allot funding to spray town trees in response to the winter moth infestation. Tisbury postponed the special town meeting until Feb. 28, when Mr. LaPiana said voters will be asked to approve the moth article.

Tisbury would use Conserve SC, an insecticide whose active ingredient is derived from the fermentation of a naturally occurring organism, on shade trees along the road, and heavily forested areas. Mr. LaPiana said there does not seem to be a pattern to the moth's location, but Holmes Hole Road and other isolated spots seem to be hit the hardest this year.

"We are not doing anything at this point," Mr. LaPiana said. "And it's not really something we're planning on until we get the funding."

Oak Bluffs highway superintendent and parks commissioner Richard Combra Jr. said the town does not have an insect control program, and they do not plan to do anything about the winter moth population. Despite seeing clusters of moths throughout the town, Mr. Combra said it would be tricky to spray along town roads to control the infestation.

"There are always a few people who don't want the chemicals on their property," Mr. Combra said. "So we're not really doing anything about it right now."