Sublethal exposure to an amitraz-fluvalinate-coumaphos mixture disrupts honeybee gut microbiota and sensitizes to...

This study evaluated how sublethal exposure to a field-realistic mixture of amitraz, fluvalinate, and coumaphos affects honeybee physiology and microbial homeostasis. Although the miticide mixture did not cause acute mortality, it significantly disrupted gut microbiota stability, reducing the abundance of key symbionts such as lactobacilli and bifidobacteria to approximately 40 % of control levels. As in vitro assays revealed no bacterial growth inhibition, the disruption likely stemmed from reduced pollen intake and suppressed feeding behavior, selectively affecting nutrient-dependent symbionts. Transcriptomic analysis revealed widespread downregulation of genes involved in detoxification, oxidative stress response, energy metabolism, and immune function, with major detoxification enzymes such as cytochrome P450s and UDP-glycosyltransferases decreasing by approximately 2-5 fold, suggesting impairment of key molecular pathways in metabolic homeostasis. Consistently, pesticide challenge experiments revealed that pre-exposure to the miticide mixture increased honeybee mortality following imidacloprid treatment, suggesting that miticide-induced physiological impairment reduced the resilience to subsequent agrochemical insults. Our findings illustrate how sublethal miticide exposures can escalate into lethal outcomes through combined risks, particularly via synergistic interactions with other agrochemicals, suggesting that current chemical-based Varroa control approaches may not be sustainable. These results highlight the urgent need to develop and adopt greener and more integrated Varroa management strategies to safeguard honeybee health and ecological stability.