I have 5 of 8 hives on screened bottom boards.  All made it through winter
(with some feeding of new splits from last year).  The three strongest this
spring were not on the screened boards (one from a late swarm from another
apiary, two established hives, one Italian, the other carniolan).  However,
the spring flow has only just started here in east TN (USA) and temps have
been unseasonably high (upper 80's).  So, those three strong colonies have a
large force out front fanning, while the rest have essentially none - their
force is our foraging.  I expect them to pretty much even out in production
in the end (as they seemed to do last year).  But after the harvest last
year, I had to feed some of the non-screen board colonies (esp. the
Italians), as we had a drought that stopped the later (minor) flows until
very late autumn.  And in mid-summer, the colonies w/o screens would have 6"
or better clusters of bees underneath, escaping the heat (I switched one to
a screen then and they all went back inside, while the others continued to
cluster outside until late in the evening).  So, the ventilation benefit
seems to be great.

K. Oland

-----Original Message-----
From: LLOYDSPEAR

I have had 100% of my hives on screen borrom boards, and have considered the
experience excellent with improved ventilation