Some say the hives leave broodless, for it makes sence being in complete darkness. Otheres claim the bees will brood all the same,
A studdy up here on formic acid treatmetn to hives within the confines of a wintering shed showed that in one situation, where they basically gassed off a studdy chamber to determine the formic tolerance on the bees, showed dead hives with brood present in them. So, that said, I think they do brood within the chamber later in winter. What triggers it, I dont know.
Swarm-trapper has suggested that fellow beekeeper he has talked to will promote brooding with humidity levels in the chamber.
I have limited experience with indoor wintering.
Last year, due to a very unusual weather year, I had caught many small late season August swarms. They entered the chamber hardly bigger than a softball. I kind of wrote them off,set my temp, and forgot about them til mid Feb. or so. They had at least doubled, some trippled in size. I actually lost some to starvation that winter due to my lack of judgement. I had no idea they would grow as sutch. I dont disturb the colonies after setting them out, so I dont know if there was brood present or not. But I can only guess that there was.
Anyhow, not to say this always happens. Perhaps there was an external factor that I was not aware of that caused this pleasent fortune.
Could of been the extreemly high amount of pollen collected late that fall, I know I greatly affected the growth of my outdoor wintered hives.
overwintering colonies in darkness sounds like it could bee a good idea if it limits the brood alittle I guess that would mean less honey consumed by the bees.I always woundered how the bees would know how the days where getting longer if they are in the winter cluster.