There is a serious outbreak of gypsy moth caterpillars this year in the Bristol Mountain area and several other locations within Ontario County.

Trees are being defoliated. This caterpillar in its later growth stage can eat up to a square foot of leaf surface in a single day. Stand near a tree and it sounds like it is raining, but it is not. What you hear are the fecal pellets from the caterpillars falling down through the tree leaves. Cornell Cooperative Extension has been receiving numerous calls and emails from home owners wanting to know what they can do? How long will it last? Will their tree die?

Trees and shrubs in the home landscape can be chemically treated with an insecticide, but time is running out. If you are going to take this action you need to do it now, within the next 7-10 days. In some cases it may be too late to be cost effective. For others the cost is just too much to have them treated. They are going to wait it out and hope for the best. Hardwood trees (oaks, maples, hickories, etc.) may be able to survive two or more years of defoliation, if they are in good health to begin with. Evergreens on the other hand are likely to die after one year of defoliation.

This caterpillar usually hatches in April and May, but with this year’s cold spring many didn’t hatch until mid-May with some not until early June. When they first hatch they are a quarter inch in size, black and fuzzy. They will hang from a silken thread and be windblown to the next branch or another tree nearby. They go through five or six growth stages depending on the sex of the caterpillar. At about one inch in size five pairs of blue dots and six pairs of red dots begin to appear on the back of the caterpillar and the hairs get longer. When full grown they are two to two and a quarter inches long and about as big around as a pencil. The caterpillar stage last about seven weeks from the time of hatch to time of pupation (cocoon stage).

Moths emerge in July and August. The male is brown with black markings and flies in a zig zag fashion. The female is white with dark markings and does not fly.

Mating and egg laying occurs during this same time period. Each egg mass contains several hundred eggs. These eggs overwinter and hatch the following spring starting the cycle over again.

The question, will next year be as bad? Often these caterpillars will be in high numbers for two or three years depending on food availability and disease pressure.

When caterpillars get stressed from lack of food and/or disease sets in we see a collapse in the population. So it is a good bet that we can expect next year to be similar to this year.

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