UK: Bees stick to working hours
Researchers from Queen Mary University of London in the UK tested that scenario during the constant daylight of summer in the Arctic Circle.
Professor Lars Chittka and PhD student Ralph Stelzer tagged 1,049 worker bees in northern Finland with radio identifiers. They thought the bees would use the extra working time of the Arctic summer to their advantage and maximise intake and colony growth.
Past studies have shown that the circadian rhythms of social insects are fairly flexible, and that these creatures can alter the expression of clock genes to fit the demands of the colony.
They tested the foraging rhythms of native bumblebees and a group of bee colonies imported into the Arctic, Bombus terrestris and B. pascuorum. But, contrary to expectations, the bees did not work round the clock.
Both species worked a day shift and were at their busiest around midday. A few hours before midnight, they returned to their nests.
"We found that bees do not naturally take advantage of this opportunity, suggesting that there is some benefit to an overnight break," explained Stelzer.
The researchers say the bees might use an external cue to tell the time in the absence of day and night cues. That external cue could be light intensity and quality or changes in temperature.
"Daily fluctuations in the spectral composition of light, especially in the UV (ultraviolet) range, could also be responsible for synchronising the circadian clock of the foragers under the continuous daylight conditions," they wrote.
"Despite the light, temperatures do fall during the Arctic 'night', so it may be that the bees need to return to their nests in order to warm their brood," the researchers said. "Also, it has been suggested that a period of sleep helps bees to remember information gained during the day's foraging."
The study is published in the journal BMC Biology.