The artist and amateur astronomer Etienne Leopold Trouvelot is known for two major lifetime achievements: 1) producing thousands of beautiful pastel illustrations that captivated the field of astronomy, and 2) introducing one of the most destructive forest pests to North America.

In the mid-1800’s, when the North’s cotton supply was interrupted by the Civil War, Trouvelot surrounded his oak woodlot in Medford, Massachusetts with an 8-foot high wooden fence and fastened a canopy of netting to protect an experimental silkworm operation. Still frustrated by predation and disease, he looked to his home country of France for a solution. Trouvelot thought that if he could cross the unpalatable Eurasian gypsy moth with the native Polyphemus, he might produce a commercially viable hybrid silkworm. But much to his chagrin, the gypsy moth was more interested in escaping than interspecies love. Realizing his blunder, Trouvelot attempted to warn local authorities, to no avail.

In 1889, residents of Medford awakened to the gentle patter of caterpillar frass raining down from rapidly defoliating trees. Nearly every surface was crawling with bristly gypsy moth larvae! The scourge, liberated from Pandora’s Box two decades prior, had finally reached outbreak proportions. Gypsy moth infestations are a serious problem, as repeated outbreaks weaken trees and lead to high tree mortality. Other effects include elimination of wildlife habitat, changes in forest composition, an increased risk of wildfire, altered nutrient cycling, deterioration in stream health, aesthetic concerns, and impacts to recreation and timber-related industries. Despite treating millions of acres of forest with pesticides and biocontrol agents, the rapacious army has managed to eat its way through New England, the Mid-Atlantic, and the Great Lakes regions.

Unfortunately, efforts to slow its spread were disastrous for other insects, especially lepidopterans (butterflies and moths). In 1906, a European parasitic fly, Compsilura concinnata, was unwisely released as a control measure. Though it failed to make an appreciable dent in gypsy moth numbers, this parasite was implicated in the collapse of our macromoth fauna, including the stunning giant silk moths, now in various states of recovery or lack thereof (Trouvelot would be relieved to know his cherished Polyphemus appears to be doing well).

Blanket spraying of broad-spectrum pesticides like DDT and carbaryl in the late 1950s to 1970s and diflubenzuron in the 1980s left a legacy of annihilation. These chemical treatments are now blamed for the possible extinction of the Appalachian grasshopper (a resident of the Poconos), the near elimination of the eastern subspecies of regal fritillary (including the eradication of a population at Gettysburg National Park), and the dramatic decline of the Appalachian grizzled skipper (a PA-responsibility species), among others. Modern treatments, such as the bacteria Bacillus thuringiensis var. kurstaki (Btk), still pose a threat to non-target lepidopterans, especially the larvae of species in the first or second instar (i.e., stage between molts) at the time of application.

Entomophaga maimaiga, a Japanese fungus introduced in the early 1900’s, has done a remarkable job controlling gypsy moth in the past few decades, allowing for more targeted treatments. The Bureau’s Division of Forest Health works closely with the Pennsylvania Natural Heritage Program to carefully plan gypsy moth spray blocks located near susceptible lepidopterans. Strategies include avoiding and buffering sensitive areas, precise helicopter (versus airplane) applications, and the use of Gypchek (gypsy moth specific nuclear polyhedrosis virus, or NPV) when available from the USDA Forest Service.

As Trouvelot demonstrated, a single person’s foolhardy decision can ripple through space and time, setting off a cataclysmic chain reaction. One might call it the “gypsy moth effect”.

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Jason Ryndock is an ecological information specialist for the Pa. Department of Conservation and Natural Resources, Bureau of Forestry.