John Wiley & Sons, Ltd.

Impact of imidacloprid on Daphnia magna under different food quality regimes

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Aquatic ecosystems are characterized by fluctuating conditions that have direct effects on aquatic communities, but also indirect influences such as changing the toxicity of chemicals. Since the effect of food quality on pesticide toxicity has rarely been studied, in the current experiment Daphnia magna juveniles supplied with four different food quality levels were exposed to a range of imidacloprid concentrations for 21 days. Food quality was expressed as carbon:phosphorus ratios of algae Pseudokirchneriella subcapitata (C:P 35, C:P 240, C:P 400 and C:P 1300). Survival, growth rates and reproduction of D. magna were monitored and the combined effects of imidacloprid exposure and the phosphorus content of algae were analyzed. A stronger effect on survival was observed at the P‐deficient diet (C:P 1300), confirmed by lower EC10 values at days 7, 9, 15 and 21 compared to diets with higher phosphorus contents. Similarly, the growth rate was reduced when D. magna were supplied with algae of low phosphorus content at imidacloprid exposure conditions. The highest reproductive output was observed for D. magna fed the optimal phosphorus diet (C:P 240), both at control and exposed conditions. It was concluded that a poor food quality increased the sensitivity of non‐target species to pesticide exposure, potentially leading to an underestimation of adverse effects on aquatic communities in the field. Environ Toxicol Chem © 2013 SETAC

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