In recent weeks billions of tiny gypsy moth larvae like these two hatched from egg masses. Each egg mass may contain more than a thousand eggs.
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 1990, gypsy moth was well established in our area and more than 130 thousand acres of trees were defoliated in Maryland and more than 100,000 acres were treated with insecticides. But the situation improved and in 2005, not a single acre of forested land was treated by regulatory agencies in Maryland. Scientists with the US Forest Service 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 four years, the gypsy moth has returned with a vengeance. This year the State of Maryland will participate in a cooperative suppression program to treat some 32,732 acres in 14 counties including Allegany, Anne Arundel, Baltimore, Carroll, Cecil, Charles, Frederick, Garrett, Harford, Howard, Montgomery, Talbot, Washington, and Worcester. Aerial spraying began last week and will continue several more. To learn if your community is part of the cooperative gypsy moth suppression program, please go to the following web site: http://www.mda.state.md.us/plants-pests/ forest_pest_mgmt/gypsy_moth/ cooperative_gypsy_moth_spray_program_2009.php
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 ofEntomophaga decimated gypsy moth populations in seven northeastern states and spread throughout much of the gypsy moth’s range. 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 recent increase in gypsy moth in our region may be linked to a weather-related decline in Entomophaga. With the return of wet weather this spring, we hope to see a return of our fungal friend which may translate into lower populations of gypsy moths. In the meantime, now is an excellent time to inspect your trees for gypsy moth caterpillars. Look for small irregular holes in the surface of the leaves. These “shot holes” are diagnostic for the presence of young gypsy moth caterpillars. Over the next several weeks, these tiny (<1”) hairy black caterpillars with a bit of brown on their back will grow into leaf-eating machines capable of consuming a square foot of foliage each day. Aficionados of the Fantastic Four will remember the battle cry of the Thing: “It’s clobbering time”. Now is an excellent time to clobber gypsy moths on your trees. But what insecticides should you use? One of the safest insecticides around is Bt. This microbial marvel is derived from soil dwelling bacteria and it is especially safe to humans, pets, and beneficial insects such as pollinators and natural enemies of pests. Bt will be used by the state of Maryland for much of its large-scale gypsy moth suppression. I treated pesky caterpillars we visited recently including euonymus leaf notcher (LINK TO APRIL 13, 2009) and eastern tent caterpillar (APRIL 6TH, 2009) and found Bt to be highly effective at killing caterpillars, especially small ones. Other insecticides in the “green” genre that brought an untimely end to my unfortunate test subjects include insecticidal soap, and products containing the active ingredients spinosad or pyrethrin. I purchased all of these products in a local garden supply store. Best results will be had if you thoroughly wet your plants and the offending caterpillars. As with any insecticide, always read the label and carefully follow all directions. A simple, green, and foolproof way to clobber a few gypsy moth caterpillars on a small tree or shrub is to simply put on a pair of gloves and crush the little rascals or knock them into a pail and destroy them. For trees too large to be safely treated by do-it-yourselfers, the best bet may be to hire a certified arborist. These professionals have the tools and talents for dealing with egregious pests of your trees. Other self-help methods for reducing gypsy moths on your trees are contained in the publications and at web sites listed below. Happy clobbering!
References
Bug of the Week thanks Dr. Paula Shrewsbury and Marvel Comics for inspiring this week’s episode.
Biology of gypsy moth: http://www.fs.fed.us/ne/morgantown/4557/gmoth/
Gypsy moth and the homeowner: http://extension.umd.edu/publications/PDFs/FS242.pdf
Controlling gypsy moth with barrier bands: http://www.hgic.umd.edu/content/documents/FS476Gypsymothbarrierbandsrev4_08_000.pdf
What areas in Maryland will be treated for gypsy moth in 2009: http://www.mda.state.md.us/plants-pests/forest_pest_mgmt/gypsy_moth/cooperative_gypsy_moth_spray_program_2009.php