By Audrey Rabalais, CG Science Editor
When entomologist Leopold Trouvelot brought gypsy moth larvae from Europe to his home in Medford, Mass. in 1869, he wanted to produce silk. When some of the caterpillars escaped from his backyard, he knew the destruction they would cause.
Within a couple years, the infestation had spread and the gypsy moth caterpillars were devouring trees around the city, said Ohio University Professor Kelly Johnson, who holds a doctorate in entomology.
According to the U.S. Forest Service, gypsy moths began to spread from Massachusetts and across New England in the early 20th century. By 1994, they entered Pennsylvania, Michigan and Ohio.
The moths move in multiple waves. Males trail-blaze, moving faster than females that are weighed down by abdomens full of eggs. The caterpillars go relatively unnoticed until they begin to satisfy their voracious appetites.
“If you’re noticing defoliation, you’ve already got an outbreak,” Johnson said.
Gypsy moths have been in Athens County for four to five years, said Urban Forester Ann Bonner, who manages Ohio’s Region 2 Forestry Program. Region 2 includes Athens, Hocking, Meigs and 12 other nearby counties. Bonner said the gypsy moth is not a stand-out species in the area because of natural control methods.
“Songbirds eat tremendous amounts of these moths,” Bonner said, adding that natural fungi in the soil also keep the moths in check.
Although there have been no large outbreaks of gypsy moths in Southeast Ohio, caterpillars took advantage of the lush Highbanks Metro Park area in nearby Franklin County. The gypsy moth larvae defoliated 10 to 14 acres of trees last summer, a substantial defoliation, according to Metro Parks Resource Manager John Watts.
The dispersal of the moths is greatly aided by human activity. Because gypsy moth mothers are indiscriminate about hatching locations, egg sacks can be found anywhere from fire wood stacks to vehicle wheel hubs. Even one egg mass is enough to start an outbreak if all the offspring survive a season, Johnson said.
To contain the moth population, the Ohio Department of Agriculture established quarantine areas. Signs are posted at campgrounds and other locations urging campers not to move firewood. The signs also include information about ways to slow the spread of the moth. Athens, Vinton and Hocking counties are included in the quarantine, which covers the entire eastern half of Ohio.
To prevent the effects of the gypsy moth larvae this year, the Department of Agriculture sprayed the previously affected area with Gypchek, a biological pesticide. Gypchek’s main ingredient is a naturally occurring gypsy moth virus known as the nucleopolyhedrovirus. The product is sprayed by a low-flying aircraft onto the treetops when the caterpillars are newly hatched. This is the first time the Highbanks Metro Park has used Gypchek.
Other pesticides are available, such as Bascillus thuringiensis (Bt), an insect bacterial disease. However, Bt is a non-specific pesticide and could kill other species of caterpillars in the area.
“We take a more conservative approach,” Watts said. “We look at a specific target and find the best agent to manage that target.”
White oak and hickory trees fell victim to the larvae more than other trees in the park.
Although last year’s affected area was completely defoliated, Watts said the trees in the Metro Parks seem to be leafing out as usual this year.
Gypsy moths thrive in many trees, but tend to be more productive on deciduous trees and especially oaks, Johnson said.
Most trees can withstand defoliation for a couple years if unstressed, Johnson said. In fact, the gypsy moths, unlike many invasive species, may act as a natural selective force that could strengthen the gene pool of affected tree populations.
“Some people would argue, and have argued, that it’s actually better to just let them sweep through and reach outbreak proportions and basically thin the stands of weak and drought-stressed trees,” Johnson said. “Then what’s left is more robust and can go for years.”
The defoliation can also benefit plants on the forest floor that had previously been out-competed by the larger trees for light or eaten by deer, Watts said. Those plants returned after the defoliation in Franklin County.
The biggest impact of the gypsy moth may not be in its effects on tree populations or other caterpillar species, but to humans expecting a pleasant woodland view in the summer months. As most foresters know, defoliation over a year will not destroy a tree population, but it is a shocking experience for those who have never seen one, Johnson said.
“If you’re there in June or July and all of a sudden you realize there’s green grass on the bottom and none of the trees have leaves on them, it’s startling,” Johnson said. “It’s a huge temporary impact.”
Temporary seems to be the key word in how the government and forest agencies are treating the gypsy moth. Much like unwanted house guests, the moths move in and cause manageable damage. Like any visitors, however, they eventually move on.