Unveiling Molecular Mechanisms Mediating Coumaphos Tolerance in Western Honey Bees (Apis mellifera)

Honey bees (Apis mellifera) are managed pollinators playing a critical role in global agriculture. Among factors linked to bee decline, the ectoparasitic varroa mite (Varroa destructor) is a major stressor. Coumaphos is an organophosphate pro-insecticide known for its selectivity toward honey bees, rendering it an effective in-hive treatment against varroa mites. This study investigated the molecular mechanisms underlying coumaphos tolerance in honey bees. Coumaphos-oxon inhibition studies with recombinantly expressed acetylcholinesterases of bees and mites precluded toxicodynamic reasons for the observed selectivity. Synergist bioassays and biochemical studies confirmed that honey bee CYP9Q2 is a key enzyme involved in coumaphos detoxification, particularly by its catalytic capacity to hydroxylate coumaphos-oxon. Bioassays with transgenic Drosophila expressing CYP9Q2 validated our molecular findings. Enzyme inhibition studies revealed suicide substrate properties for coumaphos leading to the inactivation of P450s during coumaphos oxidation. This study demonstrated the complexity of P450-mediated coumaphos activation and inactivation driving honey bee selectivity.