Gypsy moths

Gypsy moth caterpillar identification and control

By: Sandy Feather ©2008
Penn State Extension

Q. I was thinking that gypsy moths were no longer a problem near Pittsburgh, but they just killed two pine trees in my yard. I didn’t realize that was happening until a few days ago. The gypsy moth caterpillars are crawling all over my house like summers in the late 1980’s. Are gypsy moths back? What can I do to control these large caterpillars?

A. While gypsy moths (Lymantria dispar) have been pretty much under control in our area for the last 15 years or so, they will never be completely eradicated. They were introduced into Massachusetts in 1869 by Leopold Trouvelot for his silkworm-breeding program. A number of the insects escaped, and by the early 1900’s were responsible for major defoliation of forests in New England. Gypsy moths arrived in western Pennsylvania in the late 1980’s and have continued their westward movement as far as Minnesota.

Origins of the name Gypsy Moth

The common name “gypsy moth” comes from the way they move from area to area: on the wind. Their progress across the country has been slowed by our prevailing winds from the west; had they been introduced on the west coast, they would have covered the United States long ago.

White Oak leaves are easily recognized by their 'lobed' edges
White Oak is one of the favorite foods of Gypsy Moth caterpillars

When an introduced pest like the gypsy moth enters a new area, it takes a while for natural predators such as parasitic and predatory insects to kick-in. A combination of well-timed insecticidal sprays, introduced pathogens, predators and parasites worked to bring gypsy moths under control here after their initial plague-like arrival. Their populations build up to outbreak proportions every five to ten years, depending on weather conditions. A big factor in reducing the gypsy moth population to a tolerable level has been a fungus that infects and kills the pest, Entomophaga maimaiga. Years of plentiful rain help the fungus spread, while dry years cause the fungus to die out.


Appearance and Identification

If you have never had the dubious pleasure of seeing gypsy moths, young caterpillars are gray-brown and very hairy. Their hatch coincides with the leafing out of their favorite food, white oaks. Adult caterpillars are also hairy, and are characterized by five double rows of blue spots followed by six double rows of red spots on their backs.

gypsy moth caterpillar
Photo ©2008
Gypsy moth caterpillar?
5 double rows of blue spots followed by 6 double rows of red spots on its back.

While young caterpillars stay in the tree and feed day and night, older caterpillars feed only at night. They rest under leaf litter on the ground and in bark crevices near the base of host trees to avoid desiccating or being eaten by predators. Only mature gypsy moth caterpillars feed on conifers, like your two pine trees.

Mature Gypsy Moth Caterpillars

Mature caterpillars are beginning to pupate, so the window for controlling them is closing fast. You may get control with Sevin (carbaryl) or Bayer Advanced Power Force Multi-Insect Killer (cyfluthrin). If your pines are very large, you should contract a tree service with a certified arborist on staff to spray them. They have the proper equipment and training to do the job safely and thoroughly.

State foresters monitor gypsy moth populations on state and federal forestlands, and use their findings to target regions for aerial spraying. A total of 221,831 acres in 27 counties in northeastern and central Pennsylvania was treated in 2008.  The aerial sprays used by the State are biological controls, either Bt (Bacillus thuringiensis) or Gypchek (gypsy moth nucleopolyhedrosis virus). They are both very safe for people, pets, birds, wildlife, and even most other insects. Both are most effective on young caterpillars.

Forest Landowners

Private landowners in forested areas must contact their county gypsy moth program coordinators by July 15, 2008 to have their property evaluated to see if it qualifies for inclusion in the state’s 2009 gypsy moth suppression program. County gypsy moth program coordinators' contact information can be found on the Pennsylvania Department of Conservation and Natural Resources web site.

Residential property owners will have to contract with a commercial arborist to have their trees sprayed for gypsy moths.



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