I agree with Lloyd Spear, and others, that disease resistance is likely to
be present in some colonies but at the same time, and without promoting the
D.E. Hive, would say that ventilation also assists in controlling one of
them - Chalk Brood.

Well at least that is my reckoning in the UK. I might jest about the
dampness of our climate but my experience is that given a site without a
free flow of air together with a standard solid floor board will lead to
mouldy outer combs and generally severe chalk brood infestation. As for the
thought of adding wood shavings, like I read some Americans do, as an
insulating material above the cluster that would only add to the problem,
quickly becoming like going to bed with a wet mop on my head.

I am also amazed that many beekeepers go to great lengths to supply top
ventilation by placing matchsticks under the crown (cover) board. Instead
they should (at least in the UK) be taking those boards away during the
winter, only replacing them when brood rearing again starts in earnest -
maybe late January in this area. So my colonies that have mesh floors also
have a crown board, but only having half the number required of mesh floors
the remainder currently have nothing under a waterproof (important) and
secure roof. Like many things beekeeping, you eventually practice a system
which meets your requirements, and which your bees appear to appreciate.

Ken Hoare Shropshire UK