Butterfly Monitoring Data May Save Butterflies from Spray

A December meeting of groups discussing gypsy moth control in Illinois left conservationists from the Butterfly Monitoring Network (BMN) hopeful that the state will be able to use a benign alternative to the bacterial treatment it has been using to check the spread of gypsy moths.

With the gypsy moth invasion hard upon Chicago Wilderness, the Illinois Department of Agriculture (IDA) plans to treat 3,400 acres with the sprayable bacterium Btk as part of its Slow the Spread campaign this May. The IDA has placed Lake County, Illinois, under gypsy moth quarantine, while counties further south have experienced isolated outbreaks. The use of Btk concerns conservationists because it kills caterpillars of many species besides gypsy moths.

At IDA’s request, however, the Illinois Butterfly Monitoring Network (BMN) is compiling data collected by volunteer butterfly monitors over the past 18 seasons, to be incorporated into a computer map. The BMN will flag areas known to have rare butterflies and moths. They hope that such detailed information will enable Slow the Spread organizers to use a virus-based treatment known as Gypchek, which affects only gypsy moths, in the scattered places rare lepidoptera live. Gypchek, which must be isolated and approved by a federal lab each year, has often been deemed too expensive to use in large quantities.

According to Doug Taron, director of the Butterfly Monitoring Network, one species of concern is the Leonard’s skipper, which flies late in the season and is present as a very young larva when the spraying takes place. “It exists on very few wooded sites. It’s likely to be very vulnerable to this sort of thing.”

The IDA has sprayed Btk in Chicago Wilderness for several years. “The good news,” says Taron, “is that, so far, nothing has dropped out. Nothing yet that we have seen has responded in a way that you could separate gypsy moth control from a weather situation. For instance, the pipevine swallowtail at Waterfall Glen did not have a good year last year, but last year was not a good year for butterflies in general.” Still, with isolated butterfly populations exposed to so many threats, the BMN would be happy to eliminate one.

— Don Parker