Department of Natural Resources
June 21, 2021
This is a joint release issued by the Department of Natural Resources and the Michigan Department of Agriculture and Rural Development.
Gypsy moth caterpillars have been busy this spring in areas across Michigan. As these now large caterpillars near the pupal or cocoon stage, tree defoliation is at its peak.
In highly infested areas, the caterpillars' munching is audible, and round pellets of frass, or waste, rain down throughout the day and night. Oaks, aspens, willows and other host trees may be nearly leafless, or defoliated, by their feeding.
|The hairy, yellow-faced caterpillars with pairs of red and blue spots down their backs can be found on buildings, vehicles, equipment or anything that's been outside for a while.
NPV and the fungal disease have important benefits - they are specific to gypsy moth populations and do not affect people, pets or beneficial insects like pollinators or insect predators. In addition, they remain in the environment, continuing to help control gypsy moth populations every year. The fungal disease spreads best in moist springs, so this year's drought conditions may have slowed its activity.
These suppression efforts have continued to keep gypsy moth populations largely in check since the 1990s, naturalizing gypsy moth infestations into Michigan's forests. Today, gypsy moth outbreaks are cyclical, peaking approximately every seven to 10 years. In these years, the virus and the fungal disease are spread more easily through dense populations, eventually causing a crash.
|After six to eight weeks of feeding, caterpillars build cocoons. This inactive stage should be beginning now in the southern Lower Peninsula and in one to two weeks in the northern Lower Peninsula, providing a natural end to the nuisance.
Remember, some decline is natural. Removing old or stressed trees from the ecosystem is critical to allow for more vigorous regeneration to take their place.
The window for effective pesticide application has passed, but if caterpillars remain a nuisance on your property, there are a few inexpensive but effective things you can do to protect individual trees.
|Approximately two weeks after cocooning, adult gypsy moths will emerge for a short mating cycle. Females are white with brown to black markings and do not fly. Males are gray to brown with dark markings and will fly to locate females. Females produce a single, fuzzy, tan to brown egg mass that can hold over 200 eggs.
Michigan's Invasive Species Program is cooperatively implemented by the Department of Environment, Great Lakes, and Energy, the Department of Natural Resources and the Department of Agriculture and Rural Development.
/Note to editors: Accompanying photos are available below for download. Suggested caption information follows.
Caterpillar: Gypsy moth caterpillars have paired blue and red dots down their backs and tufts of hair on their sides. Photo courtesy of Karla Salp, Washington State Department of Agriculture, Bugwood.org.
Pupae: By late June, caterpillars are reaching their pupal or cocoon stage, seen here. Photo courtesy of Karla Salp, Washington State Department of Agriculture, Bugwood.org.
Egg masses: Gypsy moths' brown, fuzzy egg masses should be removed from trees, structures and equipment and properly destroyed. Photo courtesy of USDA APHIS PPQ./