Abstract
Thiamethoxam (TMX) is one of the most widely used neonicotinoid insecticides for pest control in agricultural crops. However, information on its acute and chronic toxicity for freshwater non-target insects is still limited. We aimed to evaluate the lethal and sub-lethal effects of TMX-based insecticide on Chironomus xanthus using laboratory ecotoxicological assays. Besides survival, 28-day partial life-cycle tests assessed the effects of chronic exposures on larval growth and emergence of midges. The estimated 48-h LC50 was 32 μg a. i./L of TMX. Chronic tests revealed that chironomids exposed to sub-lethal concentrations of TMX showed reduced larval growth (LOEC = 0.4 and 1.6 μg a.i/L of TMX for head capsule width and growth rate, respectively) and emergence rate (LOEC of 1.6 μg a.i/L of TMX). This study provides important ecotoxicological data concerning effects of TMX-based insecticides on tropical ecosystems and reveals that environmentally relevant concentrations of TMX can adversely affect chironomids populations. Our study also validates C. xanthus as a sensitive species to monitor the ecological integrity of tropical aquatic systems near intensive agricultural areas and to help understand the effects caused by TMX on freshwater insects.
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