Gypsy Moth Front Reaches Chicago Wilderness

The march of the gypsy moths has now reached the state of Illinois. Last year, gypsy moth caterpillars defoliated small, scattered areas over McHenry, Lake, northern Cook and northern Lake Counties, according to Jim Cavanaugh, coordinator of the gypsy moth response program for the Illinois Department of Agriculture. This year, he expects to see more. "At present, few people see the moths flying unless they...visit a small infestation pocket. These pockets are getting larger, and more people are being driven out of their yards during June and early July...The caterpillars will be on everything in the yard...[It'll be] the bugs' yard for a while."

Gypsy moths have been making their way west ever since their introduction in Massachusetts in 1882. According to U.S. Forest Service figures, the caterpillars cumulatively can defoliate thousands of acres per year before they move on. Within Illinois, the leading edge of the gypsy moth invasion lies in a swath running from Lake, Boone, and McHenry Counties, southeast through Kane and DuPage Counties to southeastern Cook County. Illinois is one of ten leading-edge states in which the moths are increasing their numbers.

According to Cavanaugh, the state's philosophy for controlling the moths is referred to as "embedded or nestled" application of pesticides. The Illinois Department of Agriculture applies a naturally occurring bacterium known as Btk to targeted areas that are infested with the gypsy moth caterpillars. These smaller areas are embedded or nestled within larger areas in which the department applies pheromone flakes to disrupt mating. The sites selected for the application of Btk and pheromone flakes are based on the previous summer's gypsy moth trap counts taken throughout the state.

While the pheromone flakes specifically disrupt the mating cycle only of the gypsy moth, the application of Btk can kill rare species of butterflies and moths within Illinois. The Department of Agriculture consults with the Illinois Department of Natural Resources, U.S. Fish and Wildlife Service, and the forest preserve districts to locate endangered and threatened species of butterflies and moths. "The real question," says Cavanaugh, however, "is which gets chosen when there is a known, serious population of gypsy moth in a sensitive lep [lepidopteran, or butterfly and moth] area? Do you save and protect the habitat quality that the rare leps depend upon or do you protect the individuals of that small population?"

Chicago Wilderness maintains that at this stage the priority should be on saving the small populations. In its recently released Wooded Lands policy paper, the coalition points out these tiny populations of butterflies and moths are more likely to blink out for good than to recolonize areas treated with Btk. While acknowledging the need for more research, the paper says that only one-tenth of one percent of mature trees are predicted to die from gypsy moth defoliation and that such defoliation could actually improve the health of many unnaturally dense woodland habitats.

More than 112,000 acres within Illinois are targeted for the application of pheromone flakes in 2004. Btk will be limited to slightly fewer than 10,500 acres in Illinois, an increase of 127 percent. Also see details concerning the specific sites of application for 2004.

— Lucy Elam