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Gypsy Moth Information
Gypsy Moth ProgramEgg Masses

Gypsy Moth Egg Masses: How to count egg masses, telling apart old and new masses, 2008 egg mass characteristics, and more.

Gypsy Moth Links

  • The USDA Forest Service has a comprehensive web site on the gypsy moth that deals with many different aspects of the gypsy moth.
  • Penn State has a fact sheet which is in the form of a web page or a PDF fact sheet.

Gypsy Moth FAQs

Q: Why were the gypsy moths so bad in 2007?

A: We experienced a dry spring, and the strong winds compounded the problem. Let me explain:

Although an introduced species, gypsy moth has achieved somewhat of a balance in the areas that it colonized a few decades ago. A fungal disease, Entomophaga maimaiga, which only kills gypsy moths, has been effective in preventing the populations from soaring to the high levels experienced in the 1980s. However, as with most fungi, maimaiga needs moisture to spread and a dry spring interfered with its action.

Some observers think that strong northwesterly winds also served to carry the early stage larvae (which blow in on long silken threads) many miles to areas which had few egg masses.

Q: How effective is B.t. at controlling gypsy moth populations?

A: Because B.t. is a protein-based biological insecticide, it has a short residual life in the forest canopy. Ultra violet rays from the sun reduce the activity of the material to less than half after 48 hours.

If the application coincides with warm weather, when the caterpillars are actively feeding, a large part of a population can receive a lethal dose and will die. However, if the weather is cold for several days, the caterpillars will not be feeding. By the time the weather warms up, much of the B.t. deposit could be gone, resulting in reduced control.

Massive populations can overwhelm a biological insecticide like B.t. especially if the conditions aren't ideal. The result would be some degree of foliage protection (The DCNR states that typically not more than 30% of the highly favored trees in a forest canopy will be defoliated), but limited population control.

Q: Why is Pennsylvania' DCNR only spraying B.t.? I hear that other insecticides can be more effective against gypsy moth?

A: The DCNR is using some funds from the federal government to provide cost-sharing for landowners. The USDA Forest Service produced an Environmental Impact Statement (EIS) in 1994 which reviewed all of the scientific studies of the control agents used in gypsy moth suppression programs. Insecticides appearing subsequent to this date were not included in the EIS and therefore cannot be used, even if they have been approved for gypsy moth control in broad-leafed forests by the EPA. A supplement to the EIS is expected in the future.

Newer insecticides (such as the insect growth regulator Confirm 2F) which have an EPA label for spraying against gypsy moth can be sprayed in suppression programs which are wholly funded by landowners.

Note: This FAQ will grow over time as new questions are asked.