I'm starting to form the opinion that it's the amount of Fat Reserves (relative to body size) and the quality of these Fat Reserves, that are more important than actual clustering ability (although that's important as well).
Isn't the Pollen used to build up Fat Reserves?
I remember reading an article (small sample I think) that showed that Amm's collected Pollen from a wide variety of plants, as opposed to some other types of bees. A varied diet may be better quality Fat for Overwintering...?
So does anyone know of Research into Fat Reserves of bees, and then Fat Reserves of different Subspecies of bees compared, and even going as far as comparing the quality of the
PS: Still have the strongest opinion that overwintering success (ability of the bee) is primarily based on the actions of the Beekeeper - including the set up of the hive, and treatments... etc.
