John Wiley & Sons, Ltd.

Interactive effects of pesticide mixtures, predators, and environmental regimes on the toxicity of two pesticides to red‐eyed tree frog larvae

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Global amphibian declines have many corroborative causes and the use of pesticides in agriculture is a likely contributor. In places with high pesticide usage, such as Costa Rica, agrochemical pesticides may interact with other factors to contribute to rapid species losses. Classical ecotoxicological studies rarely address the effects of a pesticide in combinations with other stressors. Here, we investigate synergistic roles of two pesticides (chlorothalonil and endosulfan), predator stress, and environmental regimes (controlled laboratory environments versus ambient conditions) on the survival of red‐eyed tree frog larvae (Agalychnis callidryas). We found no synergistic effects of pesticide mixtures or predator stress on the toxicity of either chlorothalonil or endosulfan. However, both pesticides were considerably more toxic under realistic ambient temperature regimes than in a climate‐controlled laboratory. Overall, endosulfan displayed the highest toxicity to tadpoles, although chlorothalonil was also highly toxic. The LC50 value (median lethal concentration estimated to kill 50% of a tested population) for endosulfan treatments under ambient temperatures was less than one‐half of that for laboratory treatments (3.26 µg/L; 8.39 µg/L). Studies commonly performed in stable temperature‐controlled laboratories may significantly underestimate toxicity compared to more realistic environmental regimes. Further, global climatic changes are leading to warmer and more variable climates and may increase impacts of pesticides to amphibians. Environ Toxicol Chem © 2013 SETAC

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