ORIGINAL ABSTRACT

Pesticide exposure remains a major driver of pollinator population decline. However, there is limited understanding of the combined toxicity of active ingredients and their adjuvants, particularly regarding its environmental risks to honey bees (Apis mellifera L.). In this study, we found that the POEA exhibited significantly higher toxicity than glyphosate. Acute toxicity tests showed that the 48-hour oral LD₅₀ for POEA and co-exposure with glyphosate was 51.306 μg·bee⁻¹ and 41.548 μg·bee⁻¹ , respectively, significantly lower than that of glyphosate (>200 μg·bee⁻¹). Both the adjuvant POEA and the co-exposure treatments with glyphosate were more toxic than glyphosate alone, while indicating a synergistic toxic effect of the co-exposure. Following chronic exposure to medium and high doses of Gly, POEA or co-exposure, it exhibited significant midgut damage and an increased rate of apoptotic cells. Further biochemical analysis revealed that the co-exposure induced oxidative stress (elevated SOD and MDA), suppressed immune (PPO) and detoxification (GST, CarE) enzyme activities, an effect which was significantly more pronounced than that induced by Gly or POEA individual exposure. Transcriptomic analysis to define the toxicity mechanisms revealed that all treatments disrupted the tricarboxylic acid cycle. Notably, the co-exposure uniquely upregulated phototransduction and visual perception pathways, implying a potential risk to foraging and homing behaviors. These findings demonstrate that POEA and its co-exposure with glyphosate threaten honey bee survival and cause tissue damage. This work provides critical methodologies and insights for improving pesticide risk assessments and guiding the rational use of adjuvants to safeguard pollinators.