Water dynamics in the honey bee colony (Apis mellifera): monitoring under high temperatures

Water is essential to the development of honey bee colonies. It is mainly used for larval jelly production and brood thermoregulation. While the mechanisms by which colonies collect water are fairly well documented, the fate of this resource within the colony is not. Understanding this could help us grasp how honey bees cope with climate change. To address this knowledge gap, we used a stable isotope approach to track the fate of water within a colony. Using 5% (v/v) deuterated water (D2O) we estimated the water turnover rate in adult honey bees, as well as the dynamics of the water used to produce larval jelly and eggs. Next, we investigated how ambient temperatures affect the water used by the colony, including bee water consumption, and the water used for the production of larval jelly and thermoregulation. Unexpectedly, our study showed that the water loss rate in adult bees is lower than in other insects dealing with a high-water-content diet, such as mosquitoes. Additionally, our results revealed the shift in the colony's water usage pattern due to the thermoregulation's need for water. At 32 °C, 80% of the water collected daily being consumed by the bees. Above 37 °C, however, this shifted so that about 50% of the water collected daily being used for thermoregulation and the remaining 50% being consumed by the bees. In conclusion, our results suggest that there may be a limit to the amount of water that colonies can collect, raising questions about their ability to cope with intense, long-lasting heatwaves.