Effects of a Thiamethoxam-Based Insecticide on the Life History of <Emphasis Type="Italic">Chironomus xanthus</Emphasis>

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.     

Low Concentrations of Glyphosate-Based Herbicide Affects the Development of <Emphasis Type="Italic">Chironomus xanthus</Emphasis>

Glyphosate is an herbicide commonly used worldwide for weed control and generally applied as part of a formulated product, such as Roundup. Contamination of surface water by glyphosate-based herbicides can cause deleterious effects in organisms, mainly in aquatic systems near to intensive agricultural areas (e.g., transgenic soybean crops). Given the lack of toxicological information concerning effects of glyphosate-based herbicides on tropical aquatic ecosystems, we aimed to evaluate the lethal and sub-lethal effects of Roundup Original® on the dipteran Chironomus xanthus. The endpoints evaluated included survival, growth, and emergence. The results showed that the 48 h LC₅₀ for glyphosate to C. xanthus was 251.5 mg a.e./L. Larval growth of C. xanthus was reduced under glyphosate exposure (LOEC for body length = 12.06 mg/L; LOEC for head capsule width = 0.49 mg/L). No effects were observed in terms of cumulative percentage of imagoes emergence. However, low concentrations of glyphosate caused delayed emergence of females (at 1.53 mg/L) and induced fast emergence of males (at 0.49 mg/L), compared to control treatment. The deleterious effects of environmental relevant concentrations of glyphosate (0.7 mg/L) observed in terms of C. xanthus growth and development suggest that glyphosate-based herbicides can have negative consequences for aquatic non-target invertebrates such as Chironomus. Multigerational assays are needed to assess the long term effects of glyphosate on C. xanthus populations. Finally, our study adds ecotoxicological data on the effects of glyphosate-based herbicides on tropical freshwater invertebrates.