We seem to be going one step forward and two steps back here. It has been fairly well established that there is no clear link between external conditions and the resumption of brood rearing. Brood rearing starts about the same time for bees kept in cold storage at a constant temp as it does for bees outdoors. If an outdoor hive is well insulated they have very little stimulus from the environment in any case. In my opinion it appears that brood rearing stops as an instinctual hold over from more primitive species. 

A break at this point would have a variety of benefits, such as interrupting disease and parasite life cycles. Presumably, once the winter bees are raised in fall, there is no reason to continue past the critical population size needed for winter, which is much smaller than the summer population. Many species *require* a dormant period before they can begin a new cycle, such as apples trees, etc.

Then, like Mike suggested, when the colony begins to cluster in late fall, the temperature in the core increases to the point where it triggers the end of the the dormant stage. Temperature is definitely a trigger to ending dormancy in a variety of organisms, but as the colony is in a cold dark place, it may in fact be the internal temperature that starts brood rearing, rather than the other way round.

plb

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