Quote Originally Posted by Jon View Post
But as others have noted above, the old cocoons get cleaned out every now and again.
As you say now and again, the images clearly show many generations of brood rearing have occurred with the real possibility of nosema spores, virus diseases and bacterial diseases lurking between the numerous layers of moults. I agree that now and again, like as in several years, the bees might rip down old black comb and rebuild it and so spreading anything that is hiding there through out the hive. Also, to equalize hive strengths, (eg in queen rearing many beeks will rearrange combs transferring excess to nucs or whatever) many persons will move frames between hives and so spreading any disease that might be there.

I still endorse a 3 year brood frame change as a sensible beekeeping practice, after all a sheet of foundation only costs about 90p and with so much AFB around at the present time everyone should be adhering to this basic practice.