Amphibians are in decline, and the causes remain controversial. Among the earliest suspected culprits were pesticides, but the role of those toxic substances is not so obvious. Only a few reports have linked amphibian declines to pesticides. And even in those few studies, the pesticide concentrations appear to be too low to kill amphibians.

But University of Pittsburgh biologist Rick A. Relyea suggests that standard toxicology may greatly underestimate the power of pesticides on frogs in the wild. In the December 2003 Ecological Applications, he shows that carbaryl, a common pesticide sold as Sevin, is much more lethal to tadpoles--up to 46 times--when the pesticide is combined with another stressor: the presence of a predator.

This article was originally published with the title Double Distress.

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