I opened the hives in my out apiary to put extra food in. I found that the colony in Hive F is dead.
This colony was given to me last May. It had been untreated for 2 years. Before that it was in an intensively managed colony.
I think that the colony died of isolation starvation. During a cold period the colony forms a cluster. Stores are used to keep this cluster warm. If the temperature in the hive is too low the colony may be unable to move around the hive. They eat the honey where they are. When this is finished they starve and then die of cold.