Temperature and CO2 concentration in honey bee hives exhibit circadian rhythms

Authors: Meikle, William; Weiss, Milagra

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2025
Publication Date: 7/1/2025
Citation: Meikle, W.G., Weiss, M. 2025. Temperature and CO2 concentration in honey bee hives exhibit circadian rhythms. Scientific Reports. 15. Article 22042. https://doi.org/10.1038/s41598-025-03614-3.
DOI: https://doi.org/10.1038/s41598-025-03614-3

Interpretive Summary: Honey bees are known to exhibit circadian rhythms (cycles of activity about 24 hours long) in laboratory studies with individual bees. However, honey bees always live in colonies with many other bees. Bee colonies in hives have been found to have 24 hour cycles in terms of temperature and CO2 concentration. This is interesting because there are many different activities needed for a colony to control temperature and CO2, yet all the bees working together produce these cycles as a "superorganism". The question is whether these cycles are truly "circadian rhythms", which are defined as 1) having 24 hour cycles that are maintained across different temperatures; and 2) having a phase (which is a measure of the start of a cycle) that can be influenced by outside factors such as light. By placing bee colonies in a cold storage unit at a low temperature without light and comparing the data with hives on the outside, we found the colonies did maintain the 24 hour cycles over time. When we introduced a light regime into the cold storage unit, we could change the phase of the 24 hour cycle. These results mean that temperature and CO2 control cycles are true circadian rhythms.

Technical Abstract: Worker honey bees exhibit circadian rhythms with respect to locomotor activity but circadian analyses have seldom been applied to colony-level behavior. Circadian rhythms have been defined as having three main characteristics: a period of approximately 24 h maintained in the absence of external cues; a period maintained over a range of temperatures; and a phase fixed by external cues from the environment. In this study honey bee colonies were subjected to two kinds of light regimes at 5 °C in a cold storage unit (CSU): (1) constant darkness; and (2) after 6–12 d constant darkness, 12 h light exposure from 6PM to 6AM (i.e. a phase approximately 12 h offset from ambient conditions). Periodogram analyses of data from the 1st light regime showed that temperature and CO2 concentration had stable 24 h periods after 20 d, as was observed for colonies in warmer temperatures in outside conditions. Period strength of temperature decreased over time in the CSU but not CO2. Cosinor analyses of data from the 2nd light regime showed a temperature phase change of about 9 h 37 min between the end of the CSU period, after 28–33 d in light regime, and after 7–12 d in outdoor conditions in the post-CSU period. The same comparison for CO2 concentration showed a phase change of about 11 h 55 min. These data indicated honey bee colonies produced circadian rhythms in hive temperature and CO2 concentration with periods both present in the absence of external cues, and with phases that can be driven by light. Rhythms associated with CO2 concentration changed with respect to light treatment more than rhythms associated with hive temperature. Based on data from longer-term (60 d) experiments, daily rhythm phases and day lengths differed significantly between hive temperature and CO2 after 15 d in the 12 l:12D light regime, and remained so in outdoor conditions.