The winter bees were too virus-ridden, due to the varroa in their cells. As such, fewer of them emerged from their cells. Many of those that did emerge will have been unhealthy. As such the winter cluster would have been smaller than it should have been, and the bees in it would have died quicker (rather than living for 4 or 5 months as you need them to). So the cluster just shrinks and shrinks, and eventually gets to the point that you see on your frames - such a tiny amount of bees that they can't survive a cold snap and freeze, or can't move to find food and starve.
Personally, given that this just looks like varroa, I would:
- Remove any old black frames, as you would do as part of routine management (good for bait hives?)
- Keep the honey frames and use for helping future colonies
- Cut out and destroy the sections of brood frames that actually have brood in (no hive wants to be given a frame with old rotten larvae in), but keep the remainder of the brood frames - doesn't look like there is anything wrong with them.
- Freeze any frames for 24 hours if you see evidence of wax moth.
But I will be interested to see if others disagree.
for the wax moth!
