Gypsy Moths: Severe Threat to Winnetka’s Landscape

Gazette Article by: Chris Fullerton
Appeared in the Gazette: Spring 1998

White oaks, featured on Winnetka’s familiar brown and white village signs, are in jeopardy. These majestic trees, some centuries old, may soon fall prey to a tiny foe whose life lasts only one year: the gypsy moth.

One of the most notorious enemies of hardwood trees, a single gypsy moth caterpillar, Lymantria dispar Linnaeus, can eat a square foot of leaves every day. Although they prefer to feast on oak leaves, the caterpillars also attack hundreds of other tree species. In 1981 gypsy moths were responsible for defoliating almost 13 million acres of forest in the eastern United States, an area larger than Rhode Island, Massachusetts, and Connecticut combined.

The presence of the gypsy moth in this country can be traced back to a specific backyard in Medford, Massachusetts. There, in the 1860s an amateur scientist, E. Leopold Trouvelot, planted on the bark of a tree an egg mass he had gathered from his native France. He hoped to produce silk. Instead, his experiment exploded into a plague that has cost the government $162 million since 1980.

Once a problem only in the East, gypsy moths have migrated to the Midwest. Their spread has rapidly increased due to recent, unseasonably warm winters—it takes three consecutive days of sub-20° temperatures to kill the majority of the moths’ eggs.

The Illinois Department of Agriculture began trapping and monitoring gypsy moths in northeast Illinois more than 12 years ago. In 1997 alone, their number increased thirteenfold. According to Stan Smith, a scientist at the Illinois Department of Agriculture, the severe problems caused by gypsy moths in the East “will probably be happening here in two to three years.”

The life cycle of the gypsy moth begins in May when larvae hatch from an egg mass containing 100–1,000 eggs. For several weeks in May and June, the caterpillars are at their most destructive. At night they chew holes in leaves, then crawl down tree trunks and rest during daylight hours. From mid-June to July the caterpillars change into pupae and become moths in late summer. The females lay their egg masses on the trunks and branches of trees. If they are not detected and controlled, they hatch the following spring, starting the cycle over again.

When moth populations are large, whole trees may be barren of leaves in summer. A healthy tree can withstand one or two consecutive defoliations of 50 per cent or more. Trees weakened by drought, stress, other insects, or diseases are less capable of recovering from defoliation and often will die quickly.

Winnetka Village Forester, Jim Stier, compares the problem facing the white oak and other deciduous trees today to that of the elms in the village in the mid-1950s. Over the course of the next two decades, Winnetka lost 70–100 elms each year. Today elms make up only five to ten per cent of the village’s tree population. Oaks, on the other hand, comprise a larger percentage of Winnetka’s tree population. An invasion of gypsy moths here would greatly affect the appearance and charm of this community.

Although their goal never has been to eliminate gypsy moths, scientists hope to slow their westward spread. Winnetkans can help. Both Smith and Stier agree that newcomers moving here from other states and residents vacationing in Wisconsin, Michigan, Indiana, and the East are inadvertently bringing the moths to the village. Buff-colored masses, approximately one to two inches in diameter, may be attached to cars, boats, furniture, camping gear, firewood, and other outdoor items. Winnetkans are urged to look for and destroy the egg masses, scraping them off and soaking them in kerosene or soapy water.

Readers who think they have found egg masses should contact the Village Forester at 501-6051, ext. 130, or the Illinois Department Agriculture at (847) 294-4343.

The white oak, symbolic of Winnetka’s past, needs our help to survive into the future.

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