MADISON, Wis. – The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) caught 99,647 gypsy moths (Lymantria dispar, the scientific name for gypsy moth) in 10,787 traps in Wisconsin this summer as part of the federal Slow the Spread Gypsy Moth Program. The following graph shows the number of moths trapped for the past five years:

Number of L dispar Trapped

“Wisconsin experienced far less rainfall than usual during the spring and early summer,” said Michael Falk, DATCP’s trapping coordinator. “These dry conditions limited the spread of diseases known to kill L. dispar caterpillars. As a result, more caterpillars survived to adulthood and populations increased for a second consecutive year.”

DATCP uses trapping to help track the size and location of moth populations. Trapping data helps determine potential sites for next year’s aerial spray treatments. For 2021, DATCP treated about 88,977 acres across 14 counties. Information about next year’s treatment sites will be available in the spring.

How to Help Lower Populations

From now until next spring, anyone can help reduce the population of caterpillars next year by treating or removing L. dispar egg masses. An egg mass is tan, oval or bulb-shaped, and a little bigger than a quarter. It has a velvety texture and can hold 500 to 1,000 eggs. These can be found on trees, vehicles, fences, playground equipment, buildings, or any outdoor item.

To remove an egg mass, use a putty knife, stiff brush, or similar hand tool and place the mass into warm, soapy water. Soak for a few days and then discard in the trash. You can also spray horticultural oil onto egg masses. Simply crushing an egg mass will not destroy it.

More Information

L. dispar is an invasive pest that has been spreading westward since its introduction to North America in 1869. Caterpillars feed on the leaves of many species of trees and shrubs, especially oaks, and can cause severe leaf loss when feeding in large numbers. For more information, call 1-800-642-MOTH (6684), email [email protected], or visit www.gypsymoth.wi.gov.

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