Temperature and CO2 concentration in honey bee hives exhibit circadian rhythms

Abstract

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.