Fenitrothion impairs honey bee physiological processes and learning ability at field levels

Fenitrothion (FNT) is a widely used organophosphate insecticide, yet the effects of chronic exposure on honey bee behavior and physiology remain poorly understood. To address this, multiple experimental approaches were employed to investigate the impacts of chronic exposure to 50 μg/kg FNT on honey bees, covering survival, food consumption, body weight, sucrose responsiveness, learning and memory, gut pathology, gut microbiota, gut detoxification enzyme activity, head transcriptome profiles, and molecular targets. We found that although FNT exposure did not significantly affect survival probability or body weight, it significantly increased sugar solution consumption and impaired sucrose responsiveness, learning, and memory performance, altered gut microbial composition and disrupted midgut morphology. Head transcriptomic analysis revealed significant dysregulation of genes associated with energy metabolism and detoxification pathways. Molecular docking analysis suggested a potential interaction between FNT and acetylcholinesterase 2 (AChE2), a known target of organophosphate toxicity in honey bees. In line with this prediction, enzymatic assays demonstrated that FNT exposure significantly inhibited AChE activity in the head. These findings suggest that field-realistic concentrations of FNT adversely affect honey bee health through multiple physiological processes and identify potential mechanisms underlying the observed behavioral impairments. This integrated understanding offers valuable guidance for the conservation and protection of bees.