Biogenic amine levels change in the brains of stressed honeybees

Three different stress treatments, CO2 anesthesia, chilling anesthesia, and vertical spin, were applied to test whether honeybee (Apis mellifera) workers express stress responses in rewarding behaviors. In the present work, we defined the rewarding behaviors as the bees flying between the hive and feeder. The results from behavioral observation show that the flight time interval of the rewarding behavior of bee workers, flying between hive and feeder, was longer when they were stressed, suggesting that the stress treatments affected the workers' rewarding behavior. The biogenic amine levels in the workers' brains were measured to examine the rapid biochemical brain response to the stressors. After the chilling anesthesia, the dopamine (DA) and octopamine (OA) levels were significantly decreased; with the CO2 anesthesia for durations of both 2 min and 4 min, only DA showed a significant decrease. In the non-anesthesia treatments, the vertical spin with a velocity of 50 and 60 rpm for 90 s, the DA and OA levels were significantly decreased. Our results suggest that when the bees were under stress, the brain levels of OA and DA were depressed, and this may have caused latency in the rewarding behavior. The serotonin (5-HT) levels under these stress treatments were not changed.