As caterpillars turn into gypsy moths, a respite for trees

DEC foresters assess outbreak damage that hit parts of the Adirondacks

By Megan Plete Postol

The statewide gypsy moth infestation has entered a new phase, as the caterpillars have become moths, and the females are now laying eggs.

The New York State Department of Environmental Conservation (DEC) has been tracking elevated populations of the gypsy moth, also known by its scientific name Lymantria dispar, that have caused noticeable damage across New York state this summer. The largest clusters of outbreaks have been in Clinton, Warren, Saratoga counties in the Adirondack region and Monroe, Livingston, Ontario, Seneca, Yates, and Orleans counties in the rest of the state.

A (vicious) cycle

Gypsy moth populations naturally spike every 10-15 years, in two to three year cycles. This year’s infestation is unusually extreme in its intensity.

“Gypsy moth outbreaks are cyclical and populations are generally controlled by natural enemies found in the environment,” DEC Forester Robert Cole said. “What allows an outbreak to start is not fully understood. New York state has experienced outbreaks of this severity in size in the past, however they are rare. Localized outbreaks are more common in areas such as the Finger Lakes and Long Island. This year, areas are experiencing tree defoliation they may not have seen in the past 40 to 50 years, such as in Clinton County.”

“This year, areas are experiencing tree defoliation they may not have seen in the past 40 to 50 years, such as in Clinton County.”

— DEC Forester Robert Cole

Throughout the spring and early summer, gypsy moth caterpillars — a native of France — showed up in clusters throughout the state, munching on the leaves of trees and leaving a path of devastation. Oak is the gypsy moths’ preferred sustenance, but they will also eat leaves from maple, apple, crabapple, hickory, basswood, aspen, willow, birch, pine, spruce, hemlock, and more, Cole said.

The gypsy moth feeding usually does not kill the tree, but can, and sometimes does. “Many trees can bounce back from being defoliated, but it does weaken the tree and can open it up to other pests,” Cole said. “After multiple years of tree defoliation, New York can expect to see pockets of mortality.”

How long will the outbreak last?

While there is little residents can do to get rid of these pests, this outbreak may not be as severe next year, due to a virus called nucleopolyhedrosis virus (NPV). 

According to DEC spokesperson Lori Severino, this virus is naturally occurring at low levels throughout gypsy moth caterpillar populations already.

“When there is a lot of competition for food and space after a population boom, the stress affects their immune response, and the virus can become lethal, she said.

It will take time to see what happens next.

“Predicting the future of gypsy moth is difficult,” Cole said. “On the positive side, we have seen caterpillar mortality caused by the virus and fungus in many areas across the state. This could lead to a significant population reduction in next spring’s caterpillars.”