University of Pittsburgh
December 14, 2003

Predators and Pesticides: Pitt Professor Reveals a Deadly Combination for Amphibians

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PITTSBURGH—University of Pittsburgh Biology Professor Rick Relyea has found that low concentrations of a globally common pesticide can be up to 46 times more lethal to amphibians when tested under more natural conditions. Relyea's research is published in the December issue of Ecological Applications.

"While pesticide tests have been traditionally conducted under highly artificial conditions, researchers ultimately want to know the impact of pesticides under natural conditions," said Relyea, assistant professor in the Department of Biological Sciences. "By adding one common environmental stressor—predation—we find that a globally common pesticide can be much more lethal than we once thought."

The pesticide tested, carbaryl, is one of the most common insecticides in the world and is sold commercially as Sevin®. It is used to control insect pests on more than 100 species of crops and in 31 million gardens in the United States. Carbaryl, like many other insecticides, acts as a toxin on the nervous system.

"Amphibians are experiencing global declines, and in some areas of the world these declines appear to be linked to pesticides," said Relyea. "However, pesticide concentrations in these areas are often low and considered nonlethal, as determined by traditional testing methods."

Pesticide tests usually examine the impact on animals in the absence of factors including the stress caused by predators that live in an amphibian's natural environment. To address this issue, Relyea exposed six species of amphibian tadpoles to predatory stress and varying concentrations of carbaryl. The red-spotted newt, a natural predator of tadpoles, was present in the environment but separated in a plastic container. The smell of the newt in the water caused the tadpoles to react to the newt as a threat, even though it could not actually harm them.

At low doses of carbaryl, there was little mortality with either carbaryl or predatory stress, but high mortality when the two factors were combined. In all six amphibian species tested, higher concentrations of carbaryl caused higher mortality