Greetings!

I participated in the study that Aaron referred to. We had about 60
colonies in four apiaries.  The hives were paired on stands and every
other pair got a screened bottom. One yard was new packages, two
yards were wintered-over bees treated for mites in spring and one
yard was wintered over untreated.

The two treated yards had very low mite count. The packages were
pretty high by September. The hives untreated in spring were all
ruined by September. The screens had no effect on honey production
(we weighed every hive and super), mite load (ether roll) or cluster
size.

Someone said even a slight difference would be worthwhile. The
problem with this is: hives vary widely so differences within a
certain margin have to be ignored. Just like the presidential polls:
they always say plus or minus a certain percentage. I would expect
with a small number of hives a this (60) the margin for error could
be fairly wide. But there was no significant difference.

This is the best study of screens I have seen. If you want to
continue to think they work, it's your right, but don't go
complaining that scientists aren't working on practical stuff for
beekeepers.

pb