Obviously there is a limit to the temperatures at which bees can survive. If you were to draw a map, you could separate the world into regions where there is no real winter; where the winters are mild enough that bees don't even cluster; where bees go into a tight cluster for many months; where bees can't survive no matter what they do. 

Much of Canada no doubt falls into this last category, and drastic measures must be taken to ensure honey bee survival. In the past most of these measures were simply not attempted because it was more economical and reliable to restock hives in the spring with bees from California. 

In my area the vagaries of winter are such that most commercial beekeepers go south for the winter. Going back in the literature it was not uncommon for beekeepers to lose 50% of their colonies to winter, back in the 1800s. This corresponds to Seeley's work which showed that something like 25% of established colonies died while 75% of newly founded colonies died over winter, averaging about 50% survival overall. 

Recent work has been done on temperature regulation in the honey bee cluster. It appears that bees do not regulate the temperature inside the cluster based on external factors, but internal ones. In other words, they rely on the insulating properties of the cluster to protect them from ambient temperatures. In other words, they use bees as an insulating blanket to prevent them from actually experiencing the ambient temperature beyond the cluster.

* * *

Stimuli of Endothermy    

We suggest the individual decision of bees to heat or not to depend on their local environment, but most probably not on the outside temperature. We do not know, however, whether the ‘local environment’ is the actual environment, or whether bees make a temporal integration on their way across the combs. Recent work has shown that especially the older age classes (‘middle aged bees’, 13–20 d) show considerable migration activity, presumably also for information sampling, beside search for work.  

Only suggestions exist about what bees measure, comb or air temperature. Besides measuring comb temperature they might just regulate [the air temperature near the bees] at a level which guarantees a minimum heat flow away from the combs. From experiments with combs cooled with a heat exchange plate, Kronenberg and Heller suggested the comb temperature to be the stimulus.

We conclude that the attempts to stabilize [the temperature of the cell rim] directly were higher than to stabilize [the air temperature near the bees], which is supported by observations of direct heat transfer to the comb surface and to the cell interior. Our data show that bees inside brood nest cells are more often endothermic than bees on the surface of brood combs. This supports the hypothesis that bees undertake special efforts to stabilize comb temperature by applying heat as near to the brood as possible. Therefore, we suggest the bees to react to comb temperature first of all and to air temperature in the second place.

Stabentheiner A, Kovac H, Brodschneider R (2010) Honeybee Colony Thermoregulation – Regulatory Mechanisms and Contribution of Individuals in Dependence on Age, Location and Thermal Stress. PLoS ONE 5(1): e8967. doi:10.1371/journal.pone.0008967
             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html

Guidelines for posting to BEE-L can be found at:
http://honeybeeworld.com/bee-l/guidelines.htm