SUMMARYThe ubiquitous use of pesticides has increased concerns over their direct and indirect effects on disease dynamics. While studies examining the effects of pesticides on host–parasite interactions have largely focused on how pesticides influence the host, few studies have considered the effects of pesticides on parasites. We investigated the toxicity of six common insecticides at six environmentally-relevant concentrations to cercariae of the trematodeEchinoparyphiumfrom two populations.

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... ll six insecticides reduced the survival of cercariae (overall difference between mortality in controlvspesticide exposure = 86·2 ± 8·7%) but not in a predictable dose-dependent manner. These results suggest thatEchinoparyphiumare sensitive to a broad range of insecticides commonly used in the USA. The lack of a clear dose-dependent response inEchinoparyphiumhighlights the potential limitations of toxicity assays in predicting pesticide toxicity to parasites. Finally, population-level variation in cercarial susceptibility to pesticides underscores the importance of accounting for population variation as overlooking this variation can limit our ability to predict toxicity in nature. Collectively, this work demonstrates that consideration of pesticide toxicity to parasites is important to understanding how pesticides ultimately shape disease dynamics in nature.