Lymantria dispar caterpillars are out and about

Oaks and many other trees are likely to be defoliated by Lymantria dispar, formerly gypsy moth, this summer in many areas of Lower Michigan.

Gypsy moth larva
Lymantria dispar larva. Photo by Karla Salp, Washington State Department of Agriculture, Bugwood.org

Lymantria dispar, formerly gypsy moth, caterpillars feed on the leaves of oaks, aspen, crabapple and 300 other species trees from late May to early or mid-July. When outbreaks occur in oak or aspen forests, more than one million caterpillars per acre can be feeding on tree leaves. Furthermore, each caterpillar can consume up to 9 square feet of leaf area during the six to seven weeks of feeding. This means trees in landscapes as well as forests can be entirely defoliated by late June. Fortunately, most hardwood trees are able to produce new leaves two to three weeks later, after the caterpillars have finished their feeding.

Outbreaks of Lymantria dispar are not frequent, but when they occur, it can be unpleasant to live, work or recreate in a neighborhood, campground or other affected areas. Several locations in Lower Michigan experienced Lymantria dispar outbreaks during the past year and populations may be high in some areas again this summer.

Lymantria dispar eggs hatch between mid- to late May across much of Lower Michigan. Young, small caterpillars are rarely noticed and cause little defoliation. As they feed, however, the caterpillars grow and consume more and more leaf tissue (see the Lymantria dispar life cycle.)

Information to help you recognize and know what to expect from Lymantria dispar, along with options to protect trees on your property, can be found at the new Lymantria dispar page at Michigan State University’s Integrated Pest Management website.

You can also use the MSU Enviroweather Lymantria Dispar Treatment Map and the MSU Enviroweather Lymantria Dispar Egg Hatch Prediction to help track and manage Lymantria dispar populations.

This insect, which is native to Europe and parts of Asia, arrived in the northeastern U.S. in the mid-1860s and has been spreading ever since. Populations of Lymantria dispar have been in Michigan since the 1980s and the first big outbreaks occurred across much of Lower Michigan in the 1990s. During the past 20 years, Lymantria dispar populations have occasionally reached high levels in some locations in Michigan, but it can be anywhere from five to 15 years between outbreaks. Lymantria dispar density usually stays high for two to three years in an area before disease and other natural enemies drive the population back to low levels. Read more about that at A Virus and a Fungal Disease Cause Lymantria Dispar Outbreaks to Collapse from MSU.

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