DCNR Management of Gypsy Moth

PA DCNR uses integrated pest management (IPM) principles to manage gypsy moth. IPM relies on survey and monitoring of the insect and its host. It involves using a variety of management techniques, such as biological, chemical, cultural, and silvicultural control to reduce the populations to less damaging levels. The choice of control method will vary depending on the site and other circumstances of each situation. Unfortunately, eradication is not the objective, because gypsy moth is already firmly established in our state.

Survey and Monitoring PA DCNR conducts egg mass surveys to determine if a spray program is needed the following season. Surveys are conducted on 1/40th acre plots in late summer. If more than 250 egg masses / acre are found, studies have shown that noticeable defoliation is likely to occur the following season. If more than 500 egg masses / acre are found, gypsy moth defoliation will likely significantly impact tree health. These thresholds are used to determine if controls are needed.

Biological control is the release of natural enemies that attack the pest. Biological controls include predators, disease organisms (fungi, bacteria, and viruses), and parasites (predators eat their prey, and parasites reproduce in their victims). Unlike chemical control, biological control is a long-term, permanent strategy to managing gypsy moth.

The DCNR reared and released 30 species of fly and wasp parasites to control gypsy moth eggs and larvae from 1964 - 2000, representing over 34 million individual insects. This included over 27 million tiny Ooencyrtus kuvanae wasps, which parasitize gypsy moth eggs, and over 200,000 Compsilura conncinata flies, which parasitize gypsy moth larvae. However, most of the other species did not establish due to a lack of alternate hosts or unsuitable habitat. The DCNR no longer conducts biological control releases due to recent increases in effectiveness of natural pathogens and the availability of more specific, less toxic chemical controls.

Chemical control The DCNR uses the bacterial insecticide, Bacillus thuringiensis var. kurstaki, or BT, to control young gypsy moth caterpillars. It works by interfering with the caterpillar's digestive system. DCNR hires contractors to spray the material on forested areas using an airplane during gypsy moth outbreaks. BT will only affect caterpillars of moths and butterflies that feed on it by consuming foliage. It is not toxic to other insects, mammals, birds, or fish. It only remains on the leaves for about ten days after application.

Gypchek is an insecticidal form of the gypsy moth nucleopolyhedrosis virus (NPV) manufactured by the US Forest Service for use by government agencies. It is in limited supply, as it requires between 500 and 1000 ground-up, infected gypsy moth caterpillars to produce enough gypchek to treat one acre. About 75% of caterpillars who encounter gypchek will die within fourteen days. Gypchek is most effective against young gypsy moth caterpillars. The DCNR plans to apply gypchek on a limited basis in future gypsy moth suppression programs. Because gypchek will only kill gypsy moth, this chemical is particularly useful in treating areas where threatened or endangered butterflies and moths occur.

Silvicultural control The DCNR can manage for gypsy moth be decreasing the percentage of preferred host trees in forest stands, although this may be challenging due to the wide variety of foods this insect will eat. Thinning stands also benefits forests by reducing competition.

Gypsy Moth Home

Forest Pest Management Home