Winter moth outbreak 'not normal'


You'd have thought it was a warm summer evening instead of a 40-degree December night the way the moths mobbed the streetlights and plastered themselves around porches and front-door lights.


Drivers who cut through large flights of moths thought they were looking at a blizzard that would guarantee a white Christmas. Some may have even rejoiced at seeing abundant life in what is a generally lifeless season.


Those monitoring winter moths, whose caterpillars devastate tree and shrub foliage in the spring, knew differently.


''It's just not normal. We're seeing huge numbers. This is a massive outbreak and a big problem. There's almost nothing preventing massive defoliation (this spring and summer),'' said Joseph Elkinton, who works in the plant soil and


insect science department at UMass Amherst.


Elkinton was one of the scientists who helped originally identify that Massachusetts and New England had been invaded by the winter moth, a European import that devastated the forests of Canada's Maritime Provinces and British Columbia in the 1950s and '60s. The U.S. outbreak started three years ago and has become worse every year. Last year saw defoliation of the deciduous forests and fruit-bearing bushes and trees across much of the Outer Cape.


Elkinton, and others, predict that even larger, more extensive areas will look like fall this summer after the caterpillars produced from this winter's mating flights feast on trees throughout most of the Cape and New England.


Trapping moths


Male moths are light brown to tan, have four wings that are fringed and are awkward fliers. Females are wingless and are often found at the base of trees, emitting a sex pheromone that attracts flocks of male suitors. After mating, the females lay eggs on tree trunks and branches, in bark crevices or under lichen.


Elkinton estimates that female moths may lay as many as 250,000 eggs per tree. Tens of thousands per tree survive to become caterpillars. Eggs hatch when the temperature averages 55 degrees. The larvae then climb trees, and produce long silken threads that catch the wind and carry them away to other trees. They are about an inch long at maturity, green with a white stripe down the side, and ''loop'' or inch along, like an inchworm.


They feed voraciously until mid-June, then drop to the ground, where they will stay in the soil in a pupa stage until they emerge in late November as moths.


The USDA has set pheromone scented traps from Maine to Connecticut to lure male winter moths and capture them in an attempt to define the boundaries of the outbreak. The bad news this year, Elkinton said, is that they appear to be expanding west, out of coastal areas where they have been confined for three years. They may already be as far west as Worcester.


Winter moths prosper here because they have no known natural predators. It is a common moth across Europe, but exists at low population levels, much like the Bruce spanworm, our native winter moth. Because they mate at night in winter, much of the bird and bat population that would prey upon them have either migrated or bedded down for the night.


But there is hope. Elkinton's UMass team and scientists at the USDA Pest Survey Detection and Exclusion Laboratory at Otis Air National Guard Base are growing flies that prey upon the moths. They released around 250 of these flies in Hingham in May.


The flies, known as Cyzenis albicans, are about the size of an ordinary housefly. They lay their eggs on leaves in the spring. When the winter moth caterpillar eats the leaves, it also eats the eggs.


A single egg will grow inside the moth caterpillar as it matures. Come November, no full-fledged moth emerges. The fly larvae has already consumed it and formed its own pupa and will hatch in spring to lay eggs and start the predatory cycle again.


It's simple, but effective. In Canada, the Cyzenis albicans flies, also native to Europe, were raised by scientists and released in great numbers starting in 1954. By 1961, the winter moth population had collapsed and was found at very low density levels that persist to this day.


Costly work


But the history of importing a non-native species to deal with imported pests has often created worse problems. The Compsilura concinnata, another fly species, was released by scientists in the early 1900s to deal with the European gypsy moth. Unfortunately, the Compsilura also attacked native moth species, devastating some of our more beautiful large moths, like the Luna moth.


Elkinton and Vic Mastro at the Otis pest laboratory say the safeguard for biocontrols of non-native species is virtually foolproof. Scientists first observe the species in its native habitat to see what preys on it.


Then they look at the predators to see what other species they attack, hoping to find a predator that preys on only the one species. That predator is then put in a quarantine laboratory with organisms that exist in our local environment to see if there is any interaction.


With the Cyzenis, Canadian scientists had already done much of the work to certify that it only preyed upon winter moths. But Elkinton is hoping to pursue research showing whether it may also affect the native spanworm species.


Still, it's not as simple to grow the necessary numbers of Cyzenis as it is to raise houseflies. Leave garbage unattended and the housefly population will bloom on its own. Because Cyzenis only preys upon winter moth caterpillars, Elkinton's team has had to go out and collect caterpillars, put them individually in test tubes with fly eggs and wait for them to feed.


Then they hope the flies hatch at the right time to be released.


It took a lot of work, with two technicians and a graduate student to raise the 250 flies that were released in May. Elkinton hopes to release 10,000 to 20,000 a year, which he estimates will cost around $150,000 a year. His work is funded through the USDA and the U.S. Forest Service.


''Once the fly (population) takes off, it will solve the problem,'' said Elkinton. But with moth populations estimated at being in the trillions and growing each year, 20,000 flies a year doesn't seem to be enough.


Elkinton said it may take millions of dollars a year to raise enough flies to bring the winter moth population under control.


That money is well spent, said Elkinton, considering the potential devastation wrought by the winter moth.


Complete defoliation for four years leads to the tree dying. In parts of Nova Scotia, for instance, 40 percent of red oak trees died from winter-moth infestation. ''It costs a lot of money to cut down and replace full grown trees. We're not talking a small impact. We're talking a serious problem that can only be solved this way,'' Elkinton said.


The state Legislature is currently working on a bill that would fund Elkinton's work.


Doug Fraser can be reached at


(Published: January 8, 2006)


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