>Incidentally, I started using no-top-ventilation in winter through the writing of Dennis Murrell. Derek Mitchell's research gave me the courage to try it through summer as well.
Same. Purely anecdotal observations but insulated tops in the summer and the winter (w/sidewalls insulation) have demonstrated less bearding and loose clusters. No venting despite the majority recommendation of northern beekeepers in my area. The SBGMI recently hosted Peggy DeSanto who is the proprietor of the Hive Hugger insulation system made the remark that when we put bees in the circumstances that we do, especially in our wintering arrangements in the North - it is "not without a price tag." This is true of almost every aspect of managed beekeeping practice. Operating with the notion to reduce colony stress to increase product output and survival makes so much sense.
Speculatively, survival has gone up due to management of the winter cluster (Mobus is a good source for consultation in this matter). No bearding in the summer and loose clusters in the winter = honeybee efficiency. Summer bees can focus on production vs. cooling and winter bees can focus on access to food/water vs. excessive heating.
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