Abstract
BackgroundHoney bee (Apis mellifera) drones and workers show differences in morphology, physiology, and behavior. Because the functions of drones are more related to colony reproduction, and those of workers relate to both survival and reproduction, we hypothesize that the microclimate for worker brood is more precisely regulated than that of drone brood.Methodology/Principal FindingsWe assessed temperature and relative humidity (RH) inside honey bee colonies for both drone and worker brood throughout the three-stage development period, using digital HOBO® Data Loggers. The major findings of this study are that 1) both drone and worker castes show the highest temperature for eggs, followed by larvae and then pupae; 2) temperature in drones are maintained at higher precision (smaller variance) in drone eggs and larvae, but at a lower precision in pupae than the corresponding stages of workers; 3) RH regulation showed higher variance in drone than workers across all brood stages; and 4) RH regulation seems largely due to regulation by workers, as the contribution from empty honey combs are much smaller compared to that from adult workers.Conclusions/SignificanceWe conclude that honey bee colonies maintain both temperature and humidity actively; that the microclimate for sealed drone brood is less precisely regulated than worker brood; and that combs with honey contribute very little to the increase of RH in honey bee colonies. These findings increase our understanding of microclimate regulation in honey bees and may have implications for beekeeping practices.
Highlights
Ambient environmental conditions fluctuate widely due to day/night and change of seasons
The major findings of this study are that 1) both drone and worker castes show the highest temperature for eggs, followed by larvae and pupae; 2) temperature in drones are maintained at higher precision in drone eggs and larvae, but at a lower precision in pupae than the corresponding stages of workers; 3) relative humidity (RH) regulation showed higher variance in drone than workers across all brood stages; and 4) RH regulation seems largely due to regulation by workers, as the contribution from empty honey combs are much smaller compared to that from adult workers
The major findings of this study are that 1) both drone and worker castes show the highest temperature for eggs, followed by larvae and pupae (Fig 1); 2) temperature in drones are maintained at higher precision in drone eggs and larvae, but at a lower precision in pupae than the corresponding stages of workers (Table 3); 3) RH regulation showed higher variance in drone than workers across all brood stages (Table 4); and 4) RH regulation seems largely due to regulation by workers, as the contribution from empty honey combs are much smaller compared to adult workers (Fig 3)
Summary
Ambient environmental conditions fluctuate widely due to day/night and change of seasons. Many social insects are able to regulate environmental conditions, such as temperature (T), relative humidity (RH), and carbon dioxide levels within their nests [1, 2]. Colonies of western honey bee, Apis mellifera, maintain their brood nest temperature around 34–36°C, which is optimal for brood development [3,4,5]. Honey bees increase colony temperature by isometric contraction of thoracic muscles to produce heat [6]. Workers fan their wings to cool the colony [14], and at the same time spread water or diluted nectar to induce evaporative cooling [15]. Honey bee workers can shield the comb from external heat sources to prevent brood from overheating [16]. Because the functions of drones are more related to colony reproduction, and those of workers relate to both survival and reproduction, we hypothesize that the microclimate for worker brood is more precisely regulated than that of drone brood
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