Investigation of the effect of temperature and colonial air on the ontogeny of circadian rhythms in young worker honey bees Apis mellifera

Circadian rhythms are essential for predicting environmental changes; however, little is known about factors regulating their ontogeny. Honey bee workers emerge from the pupae with no behavioural circadian rhythms but show strong rhythms later in their lives. Although a previous study showed that temperature in a colony plays a role in accelerating the ontogeny of circadian rhythms in young bees, it is still unknown whether there is an optimal temperature for the acceleration of the rhythm ontogeny. In the present study, we examined the influence of four different temperatures (25, 29, 34, and 38°C) for 48 h and found that as the temperature increased, more bees exhibited circadian activity rhythms for a 5 d observation period. We also examined the influence of temperature and other factors in a colony by exposing bees to air inside the hive at 34°C (a temperature nearly identical to bood nest tempearture) or 29°C. We found that regardless of whether bees were exposed to colony air, they maintained their temperature at 34°C during their first 48 h and were more likely to exhibit circadian activity rhythms during the 5 d observation period compared with bees maintained at 29°C. These results suggest that the temperature in a colony is the main factor influencing the ontogeny of circadian rhythms in young bees. We also demonstrate the presence of a critical period during which this temperature effect significantly accelerates rhythm ontogeny.