I am treating some of my hives and some are chucking out brood; most have bees outside the entrance. This is no surprise as I've seen it before. Intersting thing is that two hives side-by-side with sister queens have behaved differently. (They were mated at the same time so the same type of drones were around). One has bees hanging out of the entrance as they don't like the smell; the other has evidence of propolis over bits of the apiguard inside the hive (unlike sister) and no bees hanging out at all.
I wonder if there are any studies which relate to a hygenic trait in the bees that chuck out?