BeeCrofter asks "Has anyone done work with screened and control hives in the
manner of
scientific research?"

Researchers at two universities in the US have studied the use of screens to
control Varroa populations.  One was at the University of Florida and the
other was at Cornell University.  Papers on both were reported in American
Bee Journal.

As Aaron Morris pointed out, both arrived at the same conclusions:
* Compared to controls, mid-summer mite populations were reduced by
approximately 30%.
* By fall, there was no difference in mite population between hives with
screens as bottoms and control hives.

Thus, screens only serve to delay mite build up.  Nonetheless, that delay
may be helpful as part of an IPM approach with a goal of minimizing (not
eliminating) chemical treatment.

As far as I know, there have not been any controlled studies that focused on
effects on brood production, moisture content in honey, etc.

Lloyd
Lloyd Spear, Owner, Ross Rounds, Inc.  The finest in comb honey production.
www.rossrounds.com