we're not sure why they died. no signs of nosema or foul brood. could be mite overload as he was not monitoring for them. since they died after cold weather set in I doubt moths would be an issue. I suspect beetles depend on the bees for heat.
The beetles do depend on the bees for heat but in my OB hive they just stay in crevices above the bees even though the there are not enough bee in the upper area to keep them in the crevices.
During the summer, the bees have to keep them under constant harassment to keep them in the crevices. When the hive swarms or I open the hive, the beetles act like they own the hive for about 2 to 3 days, laying eggs everywhere. For the next week the bees are removing eggs and SHB larvae every day.