The Gypsy Moth 1996: Is the Fungus Really Among Us?

F. William Ravlin

In 1869 Etienne Leopold Trouvelot brought the gypsy moth to the United States in an attempt to "build a better silk moth". His motives were reasonably pure; solve a problem, produce a product, and maybe make a few dollars. The problem was that producing silk was not always easy because silk moth caterpillars often contracted a disease and died. Trouvelot's idea was that he might find another species that didn't have this problem - the gypsy moth (great idea Leo). The rest is history. The "better silk moth" turned out to be Pandora's box and the gypsy moth became a household word in New England. A little over 110 years later Trouvelot's "silk moth" made it's way to Virginia. The first infestations struck the Commonwealth's northern counties in 1980 and populations spread southward. Interestingly enough it was 1980 when I too made my way to Virginia (what a coincidence, another entomologist showing up at the same time as the gypsy moth) well, that's another story. Anyway, the gypsy moth has done well in the Commonwealth. Over the last fifteen years gypsy moth populations have defoliated thousands of acres each year. In 1994 452,475 acres were defoliated and in 1995, gypsy moth caterpillars consumed 850,000 acres of forested lands and impacted many residential areas with creeping caterpillars and zigging and zagging moths (the French called it "le zig zag"). Virginia, like so many states to the north, experienced caterpillars, bare trees in June, and homeowners deploying an arsenal of poisons in an attempt to save their shade trees. So what's the deal in 1996? Devastated forests, leafless shade trees, an insecticide-soaked landscape, helicopters flying overhead? I don't think so! Gypsy moth populations crashed! In 1996 there were virtually no areas of Virginia that experienced defoliation or any other gypsy moth impacts. The reason being a fungus (Entomophaga maimaiga) that was introduced in the early 1900's to control the gypsy moth (it "eats caterpillars") either reappeared or was inadvertently reintroduced in 1990. In 1996 gypsy moth was "just one of the guys" when it comes to your basic brown moths and hairy caterpillars. Populations that everyone predicted to cause problems disappeared and areas that we thought would see population increases didn't increase. So the gypsy moth is gone from Virginia and we can now put the sprayers in the garage and the burlap bands in the trash. Don't be so hasty. The fungus has indeed caused population crashes however, it is a organism and like all organisms it too, has boom and bust years (remember the gypsy moth). Note that in 1996 the Virginia Department of Agriculture and Consumer Services extended the quarantine line south to encompass a few more counties (it's still spreading). Note that new gypsy moth populations continue to appear every year. And, note that the gypsy moth has been around for longer than us humans. So, it remains to be seen what will happen in the future. If biological history repeats itself, and it usually does, the insects will have the last word and we will continue the search for the silver bullet to control "le zig zag".