My hive went into the winter with gobs of bees (carniolans), two year-old queen, two deeps: 1 brood, 1 honey; and one western super: all honey.
I insulated it with foamboard with a vent in the rear top of the hive. About 3-4 times this winter I had to wipe out the bottom of the hive of dead bees.
Each time I wiped out about two cups of bees. On good days the bees would come out and fly around. At the end of January, I put bee candy on the
inner cover because I feared they might be getting hungary, and there were lots of bees coming up throught the inner cover's hole and out the vent.
But a month ago things started to slow down. Three weeks ago the weather was really nice here, so I popped the top and took a look see..... and
there were hardly any bees left....about a hundred plus the queen-all walking around. Some of the bee candy was gone, but 99% of the honey in the western was still there, most in the second super was still there, and bottom super was plugged with dead bees.
I took off the bottom super so I could clean it out and left the other too on. Ten days later all was quiet. I popped the top again and found the rest of them dead with the queen-in a small cluster.
Not terribly surprised, though. It looked liked starvation...bee bottoms sticking out of cells. Weeks before I had scored several of the frames with honey so as to help them get to it. No signs of mites (had treated hive in the fall), but possibly
dysentery...because we had several long cold spells 0 - 20 degrees for 2-3 weeks with 2 ft. of snow. No mite poop on frames, no beetles, no moths.
Now...no bees. Tracheal mites? May be.
It gets pretty cold here....late spring, early fall, long cold wet/dry winters.