Drone honey bees are disproportionately sensitive to abiotic stressors relative to workers, despite expressing high levels of stress response proteins

Drone honey bees are the obligate sexual partners of queens, and the availability of healthy, high-quality drones directly affects the queen’s fertility and the productivity of her subsequent hive. Yet, our understanding of how stressors affect drone fertility and physiology is presently limited. We investigated sex biases in susceptibility to abiotic stressors (cold stress, topical imidacloprid exposure, and topical exposure to a cocktail of pesticides commonly found in wax), and found that drones were more sensitive than workers to cold and imidacloprid exposure, but the cocktail was not toxic at the concentrations tested. We corroborated this lack of apparent toxicity with in-hive cocktail exposures via pollen patties, where we did not observe any consistent effect of treatment on drone development or adult care. Finally, we used quantitative proteomics to investigate protein expression profiles in the hemolymph of topically exposed workers and drones, and show that drones express surprisingly high levels of putative stress response proteins, even in the negative control groups, relative to workers. These findings suggest that drones may invest in strong constitutive expression of damage-mitigating proteins for a wide range of stressors, potentially to the detriment of launching a more specific response to new stressors. Regardless of the underlying mechanism, the robust expression patterns of proteins involved in stress responses in drones suggests that drone stress tolerance systems are fundamentally rewired relative to workers, and their susceptibility to stress depends on more than simply gene dose or deleterious recessive alleles.