Thanks. Yes, good point. Basically its more effective when the colony is brood-less. Here in rural Northumberland we have had some frosts and many colonies are tightly clustered, but it is quite mild so far this winter. I’m aware that this method can be used in summer too but involves creating a brood-less state in the hive, which involves taking the queen away for a brood cycle. (this is actually less disruptive than you would think becasue the bees use up less resources raising brood)