Rare mint patch makes ideal picnic spot - natural insect repellent from a mint plant

Science News, Jan 20, 1990

Rare mint patch makes ideal picnic spot

Researchers have discovered a powerfull, natural insect repellent within the leaves of an endangered mint plant in central Florida. Even a whiff of the substance sends ants and other insects fleeing, they report in the February CHEMO-ECOLOGY.

Thomas Eisner of Cornell University in Ithaca, N.Y., grew curious about the plant, Diceranda frutescens, while walking through a patch of it at the Archbold Biological Station in Lake Placid, Fla. Its intense scent, resembling that of peppermint oil, filled the air after the biologist's walk disturbed the plants. A look at the leaves showed they were "remarkably free of insect-inflicted injury," Eisner says.

His colleagues' chemical analysis of the leaves revealed a new mint oil, which they named trans-pulegol. Moreover, the oil -- oil with a dozen other mint oils previously identified in other plants -- remains sealed in tiny capsules that act as chemical "grenades," exploding when insects chew the leaves. This allows the plant to economize its defense expenditures, releasing the compound only when needed, Eisner says. Transpulegol is the major ingredient in the grenades.

Confirming the repellent's potency, the researchers sent ants scurrying from a sugar-water feast by cutting through a nearby D. frutescens leaf. They have also identified a caterpillar that eats the mint leaves and regurgitates its stomach contents onto itself in an apparently successful attempt to repel natural enemies, including ants. The researchers are continuing these experiments with a synthetic version of the chemical they have produced in the laboratory.