OK, I’ll grant you that mold/fungus can create convenient cavities in nature for bees to live in, so can wood boring insects, rodents, and other critters. We know that bees can (and do) live in all kinds of spaces, even cellulose free places like polystyrene boxes, and old metal gas tanks. Suggesting that wet moldy conditions are required for their existence seems like a stretch to me.
And why would the bees go to all the time and trouble to coat their nest with propolis is they thrived around mold? Seems this has already been answered to some degree by a scientific study as reported by the BBC: http://news.bbc.co.uk/earth/hi/earth_news/newsid_8152000/8152574.stm
Just maybe the bees are doing the best they can to keep the mold away. :idunno:
From a practical perspective, I don’t keep my bees in trees. I keep them in hives that have been carved out with my table saw. If mold has a useful purpose beyond making holes, I haven’t seen it.
I wonder how many beeks really want to see mold in their hives over winter. :?