I checked the hives after school. Hive 3 still has brood on 3 1/2 frames, which 4 has increased to the same amount, with quite a bit of drone brood present. Hive 5 is as it was last week, but there are noticeably more bees on the frames. This is good news, as I need lots of young bees before I can raise queens. There are still very few drones though.
One of the drones I did see had a crumpled wing. This'll be due to a virus, which is spread by varroa. I've only seen it before when hives have been overwhelmed. This one was treated in January with oxalic acid, and with Apiguard a couple of weeks ago. I know for a fact that the mite load is no heavier than that in my other hives, and none of the others show a trace of it.
Another odd thing is that a couple of weeks ago, there was a small knot of bees with crumpled wings outside the hive, and every one was jet black. Over half the bees in the hive have a yellow stripe, showing that they're hybrids. I haven't seen a single crippled bee on the frames with a stripe either. I can only presume that the bees of a single patriline (ie from eggs fertilised with sperm from a single drones - queens mate about 6 - 12 times) are particularly susceptible.