Gypsy Moth

GM caterpillar pic

Gypsy moth (Lymantria dispar) is a serious forest pest and is responsible for killing millions of oak and other species of trees across the state. Although oak species are preferred, gypsy moth caterpillars feed on hundreds of other tree and shrub species, including:

  • Apple
  • Alder
  • Aspens
  • Basswood
  • Birches
  • Hawthorn
  • Hemlock
  • Tamarack (larch)
  • Pines
  • Spruces
  • Willows
  • Witch hazel

It usually takes more than one year of defoliation before trees die, however, conifers that are defoliated may be killed after a single season of defoliation.

Although the boom and bust cycles of the gypsy moth are less severe than during the past, they still require control during years their populations are high.


Perhaps the longest-standing effort to manage forest pests on Pennsylvania’s forest lands has been the DCNR’s Bureau of Forestry’s gypsy moth program.

The gypsy moth has been causing significant forest damage in Pennsylvania since the 1970s. The most recent outbreak occurred between 2013 to 2017, and this pest has been the principal agent of tree mortality on state forest land since the 1970s.

The DCNR Bureau of Forestry uses an integrated pest management approach to monitor and treat gypsy moth populations to lessen tree mortality and prevent significant defoliation.

The bureau and cooperating counties conduct annual egg mass surveys to monitor gypsy moth populations, and plans a suppression program when populations exceed threshold levels.

The bureau uses applications of Bacillus thuringiensis subspecies kurstaki (Btk), a natural biological insecticide, and tebufenozide, an insect growth regulator, to control gypsy moth populations via aerial application using airplanes and helicopters on state land and on private lands when requested by counties.


Survey your property for egg masses in the summer and fall. The gypsy moth has one generation per year in Pennsylvania.

Females lay their eggs as light tan egg masses (100-1,500 eggs/mass) on trees, stones, and other substrates during June and July. Eggs hatch from mid-April to early May the following spring.


Tactics for mechanical removal of gypsy moth egg masses can be effective for individual yard trees but are not effective as a forest-wide control method. Methods include removal of egg masses before they hatch and removal of unnecessary yard objects where egg masses can be hidden by females, such as:

  • Piles of old wood
  • Building materials
  • Dead branches, firewood, and other refuse

Egg masses should be scraped into a sealed container or bag and disposed.

Another control tactic is wrapping burlap around the trunks of trees where gypsy moth larvae can hide during the day.

The larvae hiding under the burlap are then scraped into a can of soapy water, killing the larvae.

Sticky tape around the trees can also be used to entrap larvae as they move down the trees to hide during the day.


Using insecticides to reduce defoliation during high gypsy moth densities is an effective option; however, they do not eliminate the gypsy moth entirely or shorten the infestation period.

Homeowners must assess the risks and benefits of insecticide use. Insecticides are not necessary unless the population of gypsy moth egg masses or larvae indicate a threat to your trees.

There are several insecticides registered for use for gypsy moth; however, only some of them are available for homeowner use. Always read the label instructions before using an insecticide.


DCNR conducts an aerial gypsy moth suppression program for private landowners on a request basis. This is conducted through a request for treatment by the county government.

Each participating county has a Gypsy Moth County Coordinator, who is responsible for handling all the private landowner requests in the county.

The program is conducted and cost shared in cooperation with participating counties or other local municipalities, and receives partial funding from the USDA Forest Service. Each participating county contributes a minimum of 50 percent of the total program cost.

Treatments are only conducted at the request of a landowner in a participating county, and if the area meets the program requirements. Treatments begin when 50 percent of the caterpillars are in their second instar during the spring so timing is critical.

If you believe that you have a need for a gypsy moth suppression treatment, you should contact your gypsy moth county coordinator by calling your county commissioner’s office during July or early August.

Additional information about DCNR’s private residential gypsy moth spraying program, including property requirements and landowner responsibilities is available in an informational bulletin.

If your county does not participate in the DCNR gypsy moth program, a landowner can contact one of the licensed aerial applicators to have their property treated.


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