Insulation is not about what bees can tolerate, but what conditions they work best in.
A bee colony is a single organism. Their vitals work in the same temperature ranges as yours do. If your temperature raises by 2 degC, you are in hospital with potential brain damage. If it drops by 2 deg C you have hypothermia and your limbs start dropping off. Yes, bees can survive a great range, but their essential functions -cell division and reproduction - cease outside a range of about 1-2 deg C.
EVERYTHING a bee does, or a bear, or a bat, comes down to their need to maintain their vital temperature in a very narrow band. Plants are the same: photosynthesis happens at 21 deg C in the desert and in the arctic and their whole survival strategy is geared towards achieving that. Bees collect natures rocket fuel because of their sheer energy requirements of doing so on quite a large scale. Anything you do to help means they can deploy their workforce more effectively and maintain a higher level of output.
Insulation is an option for a beekeeper. But if the bees were building their own it would be their first consideration.