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Invasive Species Spotlight: Gypsy Moth (Lymantria dispar)

June 24, 2008

Gypsy moths were brought into New Bedford, Massachusetts, from Asia and Europe in 1868. They were originally intended to be used for increasing disease resistance in hybridized silk-spinning caterpillars. Eventually the gypsy moth escaped the industry and became established in natural areas. From there, it has slowly spread throughout the northeastern states south to Virginia and west to the Great Lakes Region; it is beginning to establish itself in Illinois. (http://pest.ceris.purdue.edu/searchmap.php?selectName=ITAXAIA).

Gypsy moth larvae. Photo courtesy of www.invasive.org <http://www.invasive.org/>

Like many other insects, the gypsy moth has four life stages. Egg masses are laid in mid- to late summer; they are beige and about 3/4 of an inch in diameter. Larvae emerge from the mass in the following spring (hatching generally occurs when most hardwood trees are starting to bud). Each larva can be from 1 to 2 inches long, with hairs running down its entire body. They are grayish, with five pairs of blue spots and six pairs of red spots on their body and yellow markings on their heads. They transform into the pupa stage in midsummer from which they emerge into the adults in midsummer. Male moths are light tan to dark brown, with wavy bands, and have a wingspan of about an inch. Females are almost all white, with faint darker wavy bands on the forewings, and have a wingspan up to 2 inches. Female gypsy moths do not fly and typically lay their eggs near areas where they were feeding (including picnic tables, firewood, grills, and even cars). When these items are moved, these “hitchhikers” move with them!

Gypsy moth adults. Photo courtesy of www.invasive.org <http://www.invasive.org/>

Gypsy moth larvae are known as severe tree defoliators and can be a tremendous problem for forest land owners and managers. Oaks (Quercus spp.) are their preferred meal, but they will feed on over 500 shrubs and trees. If populations are relative small, 1 egg mass per hectare (~2.47 acres), a few trees can become infested, but damage can be limited. When large populations build up, 1,000 egg masses per hectare, the damage can become quite extensive. This could lead to entire forests being stripped of their foliage. Healthy trees can usually withstand the loss of one flush of leaves but if it happens continuously throughout the year in consecutive years it will almost mean certain failure; especially when coupled with other insect, disease, and environmental conditions.

Forest defoliation. Photo courtesy of www.invasive.org <http://www.invasive.org/>

Illinois participates in the Slow the Spread (http://www.gmsts.org/operations/) program. STS is one of the largest monitoring and action programs in the nation targeting the gypsy moth. Largely funded and managed by the USDA, this program monitors populations by employing pheromone traps for detecting the spread of the insects, to notify interested parties and establish action plans. Scientists have begun to capitalize upon natural enemies of the gypsy moth as a way to help keep their populations under control. Several of these natural enemies include the bacteria Bacillus thuringiensis (Bt), viruses Gypchek, and predatory insects such as parasitic wasps.

For more information, stop by the Illinois CAPS blog (http://www.illinoiscapsprogram.blogspot.com) for all the latest news on invasive pests in Illinois.

(Mike Garrett and Kelly Estes)

Author: Phil Nixon


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