Spring 2003

Gypsy Moths to Be Sprayed Again

As readers of last year's summer issue of Chicago Wilderness may recall (see "Gypsy Moths and Bt: A Double Scourge"), West Nile virus isn't the only troubling invasive in the sights of spray nozzles. Gypsy moth numbers are still increasing in the Midwest, and the Illinois Department of Agriculture (IDOA) — the major local coordinator for the national Slow the Spread campaign — plans a second year of treatment this May.

The IDOA intends to spray 4,000 acres regionally with the bacterial larvicide Btk, down about one-third from last year, according to Jim Cavanaugh, coordinator for the agency's gypsy moth program. The agency also plans to treat 26,000 acres with pheromone flakes (harmless except to gypsy moths), an increase of about 3,000 acres. Cavanaugh says that the adjusted numbers reflect the relative cost of the treatments — Btk costs about twice as much as pheromone flakes.

Yet many conservationists would like to see a bigger adjustment in this direction for other reasons. Spraying of Btk in areas where conservative butterfly caterpillars are feeding may do permanent harm to the scattered populations of these rare insects. Doug Taron, curator of biology at the Peggy Notebaert Nature Museum and director of the Butterfly Monitoring Network, comments that scientists can't yet determine how last year's spraying actually affected local butterflies and moths.

"Invertebrate numbers vary widely from year to year, so over short timeframes, you can't determine too much from the data," he says. Still, he argues, "We know that there is a threat in spraying because of the nature of what is being done. Clearly a lot of remnant-reliant species have been reduced to small numbers in Illinois. They are vulnerable to environmental pressures that can cause them to wink out. Gypsy moth spraying is certainly that sort of environmental pressure."

The U.S. Forest Service notes that in Michigan, which has conducted joint federal/state gypsy moth treatment programs for more than 20 years, gypsy moth damage has been minimized without threatening endangered species. In Chicago Wilderness, where remnant-dependent species occupy small habitats, conservationists continue to be concerned about the effect of such programs on our rare butterfly populations.

— Don Parker