John Wiley & Sons, Ltd.

Acute and chronic toxicity of neonicotinoids to nymphs of a mayfly species and some notes on seasonal differences

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Mayfly nymphs are amongst the most sensitive taxa to neonicotinoids. This paper presents the acute and chronic toxicity of three neonicotinoids (imidacloprid, thiacloprid and thiamethoxam) to a mayfly species (Cloeon dipterum) and some notes on the seasonality of the toxicity of imidacloprid to C. dipterum and five other invertebrate species. Imidacloprid and thiamethoxam showed an equal acute and chronic toxicity to a winter generation of C. dipterum, while thiacloprid was approximately twice as toxic. The acute and chronic toxicity of imidacloprid was much higher for the C. dipterum summer generation than for the winter one. The acute toxicity differs a factor of 20 for the 96‐h EC50 and a factor of 5.4 difference in the chronic 28‐d EC50. Temperature only had a slight effect on the sensitivity of C. dipterum to imidacloprid since we only found a factor of 1.7 difference in 96‐h EC50between tests performed at 10 and 18 °C. The difference in sensitivity between summer and overwintering generations was also found for three other insect species. These results indicate that, if the use and environmental fate of the three neonicotinoids are comparable, replacing imidacloprid by another neonicotinoid might not reduce the environmental impact on the mayfly nymph C. dipterum. The results also show the importance of reporting which generation is tested since sensitivity values of insects in the summer might be underestimated by the experiments performed with neonicotinoids and an overwintering population. This article is protected by copyright. All rights reserved

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