Impact of environmental concentrations of fipronil on DNA integrity and brain structure of Bombus atratus bumblebees

Fipronil (FP) is an insecticide used in the treatment and control of pests, but it also adversely affects bees. Currently, there is no data on the genotoxic effects of FP in the brain of bumblebees. Thus, through the comet assay and routine morphological analysis, we analyzed the morphological effects and potential genotoxicity of environmentally relevant concentrations of FP on the brain of Bombus atratus. Bumblebees were exposed at concentrations of 2.5 μg/g and 3.5 μg/g for 96 hours. After the exposure, the brains were removed for morphological and morphometric analysis, and the comet assay procedure - used to detect DNA damage in individual cells using electrophoresis. Our data showed that both concentrations (2.5 μg/g and 3.5 μg/g) caused DNA damage in brain cells. These results corroborate the morphological data. We observed signs of synapse loss in the calyx structure, intercellular spaces between compact inner and non-compact inner cells, and cell swelling. This study provides unprecedented evidence of the effects of FP on DNA and cellular structures in the brain of B. atratus and reinforces the need to elucidate its toxic effects on other species to allow future risk assessments and conservation projects.