>It shows that weak ventilation reduced heat loss and created more favourable conditions for the bees, reducing the metabolism
level, food consumption and mortality of bees and helped to preserve their energy for spring development.


"Experiments during three winters have revealed a metabolism controlling function of bee-induced hypoxia in the winter cluster. Permanent low oxygen levels around 15% were found in its core. This hypoxia was actively controlled, probably via indirect mechanisms. Varying ambient oxygen levels demonstrated a causal relationship between lowered oxygen and reduced metabolic rate (MR). Under deeper ambient hypoxia the bees switched to ultra low MR (ULMR), optional-occasional at 15% oxygen, obligatory at 7.5% oxygen. This dormancy status resembled deep diapause in insects. It stayed reversible after at least several days, and was terminated under normal oxygen at 15°C. Reduced MR via core-hypoxia is essential in water conserving thermoregulation of the wintering cluster. It allows bees to reconcile warm wintering in alert state—for defence of stores—with energy saving and longevity."

Comment: Establishing and maintaining a low metabolic rate in a winter cluster may play a role in both longevity and health as stated in the studies Randy cited. In addition to prohibiting the evolutionary adaptation discussed in this paper, adding excessive ventilation in a cold climate clearly requires that the cluster generate lots of heat for survival. The question for me is are there options for a winter cluster's survival depending on the cavity. A very tight enclosure may induce a lower metabolic rate with some biological benefits like diapause, and an open cavity may require a higher rate with unknown biological consequences. Also, it may be worth a study to figure if any of this has an effect on varroa and SHB as they over-winter in and around the cluster.  My experence of wintering is very tight boxes leads me to belive that the benefit of added ventilation is still an open issue, but I'm fully aware that others see it very differently. 

Van Nerum, K., & Buelens, H. (1997). Hypoxia-controlled winter metabolism in honeybees (Apis mellifera). Comparative Biochemistry and Physiology Part A: Physiology, 117(4), 445-455.

Bill Hesbach
Cheshire CT USA 

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