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GYPSY MOTH

* The summer of 2004 marks the first documented appearance of gypsy moth caterpillars in Shorewood Hills.  

  History: Since its introduction into the United States in 1869, the gypsy moth (Lymantria dispar), a pest of trees, has defoliated thousands of acres of hardwood forests across the northeast United States. Originally introduced into Massachusetts, the gypsy moth has spread north to Maine, West to Wisconsin, and South to North Carolina, infesting 19 states and Washington DC. Despite numerous state and local control efforts, the infestation continues to move South and West.
(Wisconsin Department of Natural Resources, 2004)

Caterpillars typically hatch in May and are very small (~ 1/8").  When they first hatch, the larvae produce silk threads with which they can travel long distances in the wind (ballooning).  As the caterpillars feed and become larger (1 to 2"), they typically will stay in the same tree throughout the summer.  Most of the damage to plants (primarily trees) occurs later in the summer as the full grown caterpillar consumes more and more food.  Oak trees are a favorite and when caterpillar populations are high enough the result can be near complete defoliation.  Several years of defoliation can lead to death of a tree (one year of defoliation can lead to death if the tree is already stressed).  Other favorite foods of the gypsy moth caterpillar include:  aspen, cottonwood, willow, basswood or linden, elm, birch, hawthorn, crabapple, apple, and other fruit trees (they are not fussy eaters).  If their favorite foods are gone, they will begin to target other types of plants.  The caterpillars will finally begin to stop feeding and pupate in late summer (end of July and August, depending on weather and other environmental factors).

LATE APRIL: Place barrier bands on tree trunks.

Barrier bands will prevent caterpillars from climbing back into trees after ballooning or when they have fallen. Barrier bands can be purchased or made using duct tape or other nonporous material that can be wrapped around a tree trunk and coated with a commercially available sticky material such as TangleFoot®. NEVER put sticky material directly on the tree trunk. On thin-barked trees, tie butcher paper or paper bags around the trunk before using the duct tape. The sticky material may need to be re-applied periodically due to rain and other environmental conditions as well as when the bands are covered with caterpillars.
(Wisconsin Department of Natural Resources, 2004)

MAY–JUNE: Apply insecticides. If you choose to use pesticides to control the caterpillars, they must be applied at this time. There are two options: biological and chemical pesticides. For assistance in applying insecticides, consider contacting a certified arborist or pesticide applicator. Biological pesticides. The most common treatment used against gypsy moth is a spray of Bacillus thuringiensis, commonly called Bt. This bacterial insecticide kills caterpillars that eat it within a week of its application. Bt causes the cells of the caterpillar’s stomach lining to rupture. Bt is found naturally in soil and degrades within a week when exposed to sunlight. The variety of Bt used against the gypsy moth only affects caterpillars of moths and butterflies. Bt has no affect on animals, birds, people, or even other insects. It is sold under various labels (Bactur, Dipel, Foray, and Thuricide, to name a few). Bt must be applied to trees in May when caterpillars are less than 1/2-inch long. Timing is critical as Bt is significantly less effective on older caterpillars. Chemical insecticides. Numerous insecticides are registered against gypsy moth in Wisconsin. Many products are available at your local garden center or nursery. Check the label to make sure gypsy moths are listed. Acephate, carbaryl, and malathion are the most common active ingredients and are available in several formulations. If you elect to use a chemical insecticide, consider the potential impact on beneficial insects and natural enemies such as predators, parasites, and honeybees. ALWAYS read and precisely follow the label directions.

EARLY JUNE: Replace barrier bands with collection bands. Collection bands can be made from medium-weight dark cloth or burlap approximately 12–18 inches wide and long enough to completely wrap around a tree. Using a piece of cord or twine, fasten the middle of the cloth band to the trunk at chest height. Fold the top half of the cloth down to cover the bottom half. Older caterpillars are attracted to these “skirts” when looking for a place to hide during the day. Remove and destroy the caterpillars each day by scraping them into a bucket of soapy water.

(Wisconsin Department of Natural Resources, 2004)

Moths will begin to hatch from their pupa in late summer (usually in August).  The male moths will immediately begin to fly around in search of female moths to mate with.  The females will lay their egg masses as soon as a male finds her.  See the moths below:

Female moth:  larger than male and cannot fly (lays egg masses)	Male moth: smaller and can fly

The egg masses are the most important stage to find and destroy.  Each egg mass can contain several hundred to a thousand or more eggs.  They will hatch in late spring (late April, early May).

Egg masses:  see the white female moth laying eggs.	Egg masses:  see the 2 moths laying eggs on the tree.

MID-OCTOBER—MID-APRIL: Destroy egg masses.

Destroy egg masses by spraying them with Golden Pest Spray Oil (formerly Golden Natur’l Oil) or by scraping off egg masses and killing them. Treating egg masses with Golden Pest Spray Oil is preferred if you plan on participating in a suppression spray as it leaves the egg masses in place to be counted by the programs surveyors. Golden Pest Spray Oil should be mixed 50/50 with water and then spritzed onto the egg mass until it is soaked. If you scrape off egg masses, use a knife to scrape all of the eggs into a jar. Eggs can be killed by microwaving 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.
(Wisconsin Department of Natural Resources, 2004)