Merry Chris-moths emerge

By Janet Hefler - December 29, 2005

It was not exactly the kind of white Christmas everyone hoped for last weekend, with thousands of fluttering winter moths mimicking the appearance of holiday snow flurries.

Probably few recognized them as the adult version of the tiny, pale green "inchworms" that infested the Island last summer, along with tent and gypsy moth caterpillars. The one-inch winter moth caterpillars (Latin name Operophtera brumata) fed voraciously until late June, defoliating shade and fruit trees, and shrubs, and then dropped into the ground to pupate.

They began to emerge as pesky, adult winter moths around Thanksgiving time, continuing through December. Recent mild weather helped hatch the bumper crop of uninvited holiday guests that swarmed into Vineyard houses every time a door opened.

About a week ago, the appearance of the small, gray, wingless female winter moths was a harbinger of things to come. Clinging to pretty much any available outdoor surface, they waited patiently for the arrival of their Prince Charmings holiday revel.

They were not disappointed, as evidenced by the swarms of eager, light brown, winged male suitors observed enjoying their company during the weekend's warm weather. Primarily attracted to lights and females, the male moths must have found the holiday especially merry, with this year's abundance of willing partners and bright Christmas lights.

Although the females usually deposit their egg clusters on trees, it appeared that any hard surface would do. Some homeowners found the dark green eggs, which look like small mud splatters, not only on decks, shingles and siding, but on windows and glass doors, as well.

The sheer volume of the female winter moths' job may have caused their indiscriminate deliveries, with each one laying up to 150 eggs. That number becomes significant

when looking at the results of a 2004 winter moth study conducted by Brenda Whited at the University of Massachusetts.

In studying population density, she and a team collected and counted female winter moths. On just one tree in West Bridgewater, 1,619 females were counted, and those represented only the ones that were caught. Multiply that number by 150 eggs, and the total comes to about 243,000 eggs on one tree. With several million trees known to be infected, the number of winter moths is estimated to be in the trillions.

Although the adult winter moths will soon die off, their eggs will hatch in the spring or whenever temperatures average around 55 degrees, which could be as early as March. Then the cycle begins again, with the tiny winter moth caterpillars feasting on budding leaves in virtually any tree or shrub.

Some of their favorites include maples, oaks, apple and cherry trees, blueberry bushes and Rhododendrons. State officials estimate the moths defoliated more than 20,000 acres in eastern Massachusetts last year.

Many Vineyarders may remember how annoying the tiny, newly hatched inchworms were last summer, dangling on invisible silken threads from tree branches and dropping on heads or hitting faces. The caterpillars were waiting for the wind to carry them to other trees, a process known as "ballooning."

According to University of Massachusetts Extension specialists and other experts, the winter moth is an invasive species native to Europe and has no natural predators here. The first winter moth infestations in North America were confirmed in Nova Scotia in the 1950's, and in the Pacific Northwest, on the other side of the continent, in the 1970's.

No one is quite sure how the winter moths gained a foothold in Massachusetts, first detected in 2003. The highest populations are found on Cape Cod and in Plymouth and Essex counties.

Trying to kill the winter moths in their adult stage is futile, according to Charles Burnham of the Massachusetts department of conservation and recreation, because they do not feed at this time.

UMass Extension experts suggest that a dormant oil spray applied to the trunks and branches of trees in very late winter or early spring may be helpful in killing the over-wintering eggs before they hatch.

The oil sprays should be applied when the outdoor temperature is above 45 degrees and should not be applied when temperatures may dip below freezing for 24-48 hours after application. However, the spray may achieve only limited results, as the oil must cover the eggs and may not reach the countless numbers hidden in tree bark crevices and under lichen.

Using sticky tree bands to capture the adult moths and/or caterpillars has not proven effective either. The adult moth population is too high for their capture to make a difference, and the caterpillars can avoid the bands by ballooning to untreated trees.

The caterpillars may be managed in the very early stages with products labeled as containing Bacillus thuringiensis kurstaki (B.t.k.).

Two other products suggested for use by homeowners against caterpillars of all ages are "Bulls Eye BioInsecticide" and "Monterey Garden Spray," which contain a bacterium that affects the insects' nervous systems. Commercially licensed pesticide applicators use a stronger variety, "Conserve," and usually charge a per-tree spraying fee.

A promising method for controlling the winter moth population is under development by Joseph Elkinton, a forest entomologist and professor at UMass-Amherst. He is breeding the winter moth's only known predator, Cyzenis albicans, a parasitic fly that lays its eggs on the foliage of plants the winter moth caterpillars are likely to eat. They ingest the fly eggs, which hatch inside them and kill them.

It will likely take several years for the flies to make a dent in Massachusetts' winter moth population. The fly was introduced in Nova Scotia in 1954, effectively bringing the winter moth population under control in about six years. Mr. Elkinton has collected the flies in Nova Scotia and bred them in cages at Otis Air Base for release in several locations across Massachusetts in the spring of 2006.