Bumblebee foraging rhythms under the midnight sun measured with radiofrequency identification

Area of Science:

• Ecology
• Animal Behavior
• Chronobiology

Background:

• Arctic regions offer unique 24-hour daylight for bumblebees to maximize foraging and colony growth.
• This study investigated the foraging rhythms of bumblebee (Bombus terrestris and B. pascuorum) colonies in northern Finland under continuous summer daylight.
• Over 1,000 workers were monitored using automated radio-frequency identification to analyze their circadian foraging patterns.

Purpose of the Study:

• To determine if bumblebees utilize the 24-hour daylight period in the Arctic for continuous foraging.
• To analyze the circadian foraging rhythms of Bombus terrestris and Bombus pascuorum colonies.
• To identify potential environmental cues that entrain bumblebee circadian clocks under continuous daylight.

Main Methods:

• Utilized fully automatic radio-frequency identification (RFID) for monitoring.
• Tracked foraging activity of over 1,000 bumblebee workers (Bombus terrestris and B. pascuorum).
• Analyzed circadian foraging rhythms and activity patterns over the 24-hour period.

Main Results:

• Bumblebee foragers exhibited robust diurnal rhythms, not continuous 24-hour activity.
• 95.2% of Bombus terrestris workers showed diurnal rhythms with a mean period of 23.8 hours.
• Foraging activity was restricted to specific daily periods (e.g., 08:00-23:00 for B. terrestris, 06:00-22:00 for B. pascuorum), with minimal activity during the night.

Conclusions:

• Bumblebee circadian clocks are entrained by external cues despite continuous daylight.
• Daily cycles in light intensity and temperature are likely primary synchronizing agents.
• UV light spectral composition may also play a role in synchronizing bumblebee circadian clocks.