Hygroregulation, a key ability for eusocial insects: Native Western European bees as a case study

Abstract

Sociality has brought many advantages to various hymenoptera species, including their ability of regulating physical factors in their nest (e.g., temperature). Although less studied, humidity is known to be important for egg, larval and pupal development. Two subspecies of Apis mellifera of the M branch, also called black bees, were used as models to test the \"hygroregulation hypothesis\", by means of monitoring hygrometry in hives during one year in four conservation centers: two in France (A. m. mellifera) and two in Portugal (A. m. iberiensis). We investigated the ability of both subspecies to regulate the hygrometry daily, but also during the seasons and one complete year. Our data and statistical analysis probed the capacity of the bees to regulate humidity in their hive, regardless of the day, season or subspecies. Furthermore, the study showed that humidity in beehives is very stable even during winter, when brood is absent, and when temperature is known to be less stable in the beehives. These results would support that hygrometry could prevail over temperature in maintaining nest homeostasis, maybe because of a bigger importance of hygrometry for all the population during a year, or because of the imprint of the evolutionary history of this hymenopteran lineage.