In the late 1860’s a misguided French artist and scientist named Etienne Leopold Trouvelot returned from France to his American home in Medford Massachusetts with egg masses of the gypsy moth. The reasons for transporting the alien insect remain shrouded in history, but the wily gypsy moth managed to escape the confines of Trouvelot’s laboratory and infested oak trees behind his home. Trouvelot notified local officials of this accident, but to no avail. No early steps were taken to eliminate this pest and it established in the hardwood forests of New England. In the intervening 140 years gypsy moth has become the most significant pest of hardwood trees like oak, beech, and hickory in the eastern United States. During years of peak activity in the early 1980’s the gypsy moth was responsible for defoliating more than 12 million acres of forest and shade trees nationwide. The gypsies moved south and west from New England spreading their wave of destruction. By the early 1990’s, gypsy moth was well established in our area and more than 130 thousand acres of trees were defoliated in Maryland in 1990. The high water mark for spray programs to control gypsy moth in Maryland was 1990 when more than 200 thousand acres were treated. But the situation improved and in 2005 for the first time since 1979, not a single acre of forested land was treated by the state. Scientists with the US Forest Service have discovered an intriguing pattern of waxing and waning in gypsy moth populations in cycles or 5 to 10 years. What drives these cycles is a biological riddle yet to be definitively resolved. However, in the past three years, the gypsy has returned with a vengeance. This year the state of Maryland plans to treat roughly 100,000 acres of Maryland’s forests to control the gypsy moth. The counties included in the 2008 Gypsy Moth suppression program are: Allegheny, Anne Arundel, Baltimore, Carroll, Cecil, Frederick, Harford, Howard, Garrett, Montgomery, Talbot, Washington, and Worchester. One of the key factors holding the gypsy moth at bay is a fascinating fungal disease called Entomophaga maimaiga. This fungus is native to Asia and was released in New England. In 1989 an epizootic of Entomophaga decimated gypsy moth populations in seven Northeastern states. It spread throughout much of the range of gypsy moth where it maintained gypsy moth at innocuous levels in most years. Unfortunately, much of the country including Maryland has been wrapped in drought for several years and drought is the enemy of fungus. It appears that the tremendous increase in gypsy moth in our region may be linked to a weather-related decline in Entomophaga. If you had a problem with gypsy moth last year, a few actions may be taken at this time to help reduce damage to your trees later this spring. Gypsy moth eggs will hatch within the next several weeks around the state. Now is the last chance to remove egg masses from all infested trees, structures, and lawn items by scraping them into bags for disposal or into solutions such as soapy water. Be careful not to inhale the tiny brown hairs that cover the egg masses and do not handle the egg masses without gloves. Some people are allergic to the hairs. You may also consider using sticky barrier bands to prevent gypsy moth caterpillars from crawling up tree trunks and into tree canopies where they feed on the foliage. Sticky barrier bands can protect trees from defoliation by preventing primary and secondary invasions by caterpillars. Bands should be in place before the eggs hatch and must be maintained all season. Sticky barrier bands prevent the primary invasions of newly hatched caterpillars from egg masses found near the base of a banded tree, in surrounding leaf litter, in woodpiles, or on nearby lawn furniture. Sticky barrier bands also prevent three types of secondary invasions of gypsy moth caterpillars. First, many young caterpillars hang by silken threads from tree branches or foliage and are then dispersed by the wind. These “ballooning” caterpillars generally fall to the ground. Sticky barrier bands can prevent caterpillars from reentering the treetop. Second, older caterpillars that began life in the tree, above the band, and did not balloon out of the tree when very young, still periodically drop out of the tree’s canopy because of irritation by natural enemies, wind, or rain or for other unknown reasons. The larger the population, the more likely caterpillars are to move out of trees. The sticky barrier band can prevent infestation of the tree by these larger caterpillars. Finally, large caterpillars may swarm into your yard from neighboring properties where the trees have been completely defoliated. Well-maintained barrier bands help protect your trees from this late-season threat (typically occurring about mid-June). Alas, barrier bands have not proven to be effective under all conditions of gypsy moth infestations, but they still may be worth a try.

Our special thanks to Mary Ellen Setting for providing information on the status of gypsy moth in Maryland and to Howard Bernstein for providing the inspiration for this Bug of the Week. Fortunately, there are many fine sources of information regarding the biology and management of gypsy moth.

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