Predator cues and pesticides: A double dose of danger for amphibians.

Amphibians are declining globally, and biologists have struggled to identify the causes. Pesticides may play a role in these declines, but pesticide concentrations in nature often are low and considered sublethal. Past research has found that the globally common pesticide carbaryl can become more lethal under different environmental conditions including differences in temperature and competition. A recent study has found that predatory stress, a situation common for most amphibians, can make carbaryl 2–4 times more deadly to gray tree frogs (Hyla versicolor). To determine whether this is a general phenomenon in amphibians, I examined how carbaryl affected the survival of six amphibian species in the presence and absence of predatory stress. Higher concentrations of carbaryl caused higher mortality. In two of the six species, carbaryl became even more lethal when combined with predatory stress (up to 46 times more lethal). This suggests that apparently safe concentrations of carbaryl (and perhaps other pesticides with similar modes of action) can become more deadly to some amphibian species when combined with predator cues.