Bees observe a strict working day, even in conditions of 24-hour sunlight. Researchers writing in the open access journal BMC Biology tagged worker bumblebees with a radio identifier, similar to an Oyster Card, which was used to monitor their movements during the constant light of the Arctic summer.
Ralph Stelzer and Lars Chittka from Queen Mary University of London, UK, carried out the study at a research station in Northern Finland. According to Stelzer, "Constant daylight would seem to provide a unique opportunity for bumblebee foragers to maximise intake, and therefore colony growth, by remaining active during the entire 24-hour period. We found that bees do not naturally take advantage of this opportunity, suggesting that there is some benefit to an 'overnight' break".
The researchers studied both native bees and a group of bee colonies they imported into the Arctic. Both species worked a day shift, with maximum activity around midday, and retired to their nests well before midnight. Stelzer and Chittka speculate that the bees must have some way of telling the time in the absence of day/night cues, suggesting that the insects may be sensitive to light intensity and quality or changes in temperature.
Speaking about the possible advantages gained by taking some time off, the researchers said, "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. Also, it has been suggested that a period of sleep helps bees to remember information gained during the day's foraging".
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More information: Bumblebee foraging rhythms under the midnight sun measured with radiofrequency identification, Ralph J Stelzer and Lars Chittka, BMC Biology (in press), www.biomedcentral.com/bmcbiol/