Sleep Research on Honeybees: Neurophysiology and Behavior

Abstract

Observations and experiments on forager honeybees under various conditions have revealed that, when these insects rest at night, they exhibit phenomena which are strongly reminiscent of several features characteristically accompanying sleep in humans and mammals. In an observation hive at night, large numbers of bees remain stationary for long periods of time. These bees are not actively engaged in maintenance of hive temperature. In the laboratory (under various conditions), individual forager bees show daily or circadian rest-activity rhythms. At night, the following phenomena have been observed in intact bees: isolated, individual animals remain at one location for extensive periods of time during which only sporadic overt activity (e.g., grooming) can be observed; thoracic temperature falls to the prevailing environmental level (25°C); the threshold for elicitation of a behavioral reaction rises; antennal motility gradually declines and the antennae assume characteristic positions which are also seen in resting hive bees, at night. Long-term recordings from visual interneurons in bees revealed the following features: the sensitivity of neurons in the lobula to visual stimuli (moving patterns) declines at night but can be transiently restored by mechanical or strong visual stimulation. Neuronal sensitivity and spontaneous activity fluctuate with a circadian rhythm. Electromyographic activity recorded from the bee’s neck muscle 42 over several days show a progressive reduction in amplitude during the night. The corresponding overt expression of this decrease in neck-muscle tone is the gradual increase in the inclination of the head. The results obtained to date support our hypothesis that forager bees do, in fact, sleep at night.