Gypsy Moth

Where did all of those Gypsy Moth caterpillars go? In accordance with the Wisconsin Department of Natural Resources Gypsy Moth Program the Park & Forestry staff have coordinated three aerial spray application of chemical (Btk) to control the ever growing population of gypsy Moth caterpillars. Chemical applications occurred in different areas of the city during the past three years, totaling 592 acres. After the spring 2004 application West Bend received an extended period of cool wet weather which allowed a natural occurring fungal pathogen to also help in controlling this pest. This pathogen was prevalent throughout the State of Wisconsin and we are happy to inform the residents that West Bend will not require a chemical application in 2006. We will continue to monitor this pest during 2006 for possible infestations. If you have any questions call 335-5080.

What’s all this about gypsy moths?
The gypsy moth was accidentally imported from Europe and Asia more than 130 years ago. This insect feeds on the leaves of more than 500 species of trees. Unfortunately, many of its favorite trees are those here in Wisconsin and your backyard. Among the favorite trees are oaks, basswoods, birches, willows, crabapples, aspens, pines, and spruces.

Gypsy moth caterpillars are the only feeding stage of the insect and can be found feeding on the leaves of these and other trees any time from the beginning of May until early July. These caterpillars can be hard to identify in May and early June when they are very small, but by mid-June they are large enough to see their distinctive features. The gypsy moth caterpillars have distinct red and blue spots on their back which separates them from other hairy caterpillars. They do not make tents, and after feeding as caterpillars, they enter the pupal (or cocoon) stage for about two weeks (early to mid-July). The adults emerge from the pupal cases in mid to late July. Males are browning gray with large antennae and are agile fliers, while the females are white with black markings and cannot fly. Adults are seen from the middle of July until early August.

Gypsy moths spend approximately 9 months in the egg stage, from late July or August until the following May. Fortunately, gypsy moth egg masses are very recognizable. They can be up to 1 ½ inches long and 1 inch wide (though smaller ones are common), and are often drop-shaped. The egg masses are hairy and look like tan or yellow felt. Egg masses can contain up to 1000 eggs, and each female deposits one egg mass. Egg masses can be found in many locations. In forests, they are found primarily on the trunk and the underside of tree branches. In residential areas, egg masses are found on almost everything – houses, gutters, firewood piles, birdbaths, lawn furniture, and vehicles.

Trees can withstand up to 50% loss of leaves without negative effects, but 75% or more loss makes trees susceptible to pesky insects and disease.

What can I do?
Late April: Place barrier bands on tree trunks. Barrier bands can be made with duct tape (sticky side out) or other non-porous material that can be wrapped around a tree trunk. If you are not using duct tape, you can coat the material with commercially available sticky material. Due to rain and other weather conditions the sticky material may need to be re-applied.

Early June: Replace barrier bands with cloth collection bands. Using a medium weight fabric such as burlap, cut the cloth 12 to 18 inches wide and long enough to wrap completely around the tree trunk about chest high. Tie the cloth band with string or twine, then fold the upper portion down to form a "skirt" abound the tree.

Caterpillars collect under the cloth during the morning hours as the day begins to warm up. Sweep the gypsy moth caterpillars from underneath the cloth into a bucket of soapy water every day. The soapy water kills the caterpillar immediately. Use a small brush, or gloved hands to remove the caterpillars from the cloth because some people experience an allergic reaction to the "hairs" on the gypsy moth caterpillar.

Winter (mid-October until mid-April): Destroy egg masses. Since a single egg mass contains 600-1000 eggs, each egg mass destroyed can prevent the hatching of several hundred caterpillars. Did you know that a single caterpillar can consume nearly a square yard of foliage in its lifetime? Destroying one egg mass can save a lot of leaves.

You can destroy egg masses by spraying them with Golden Pest Spray Oil (formerly Golden Natur’l Oil) or by carefully scraping off egg masses and killing them. Golden Pest Spray Oil should be mixed 50/50 with water (follow the label directions) and then sprayed onto the egg mass (with a spray bottle) until it is soaked. Add food coloring to the mixture so that you can identify which ones you have treated (bright blue egg masses really stand out). If you scrape off egg masses, use a knife to scrape all of the eggs into a bag or a jar. Eggs can be killed by micro waving them on high for 2 minutes or by soaking in soapy water for 2 days before discarding them in the trash. Don’t just scrape egg masses onto the ground or try to crush them with your shoe, as they will survive to hatch next spring.

What is the City of West Bend doing about this problem?
At this time, the City has completed the egg mass counts and has provided the DNR with all pertinent grant information. The City anticipates a decision from the DNR in late December. If areas are infested with over 500 egg masses/acre and this amount is

maintained over a 20 acre area, only then (no exceptions) will this area be eligible for an aerial application the following spring. Aerial applications do not remove all caterpillars; it controls the number of caterpillars within that particular area.

For more information on gypsy moths check out:

UWEX and DNR website at:

USDA Gypsy Moth Manual at:

1115 S. Main Street
West Bend, WI 53095
(262) 335-5100


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