Aaron and I sat in the same meeting where Dr. Calderone presented his data that would cause one to believe that screened bottom boards (OMB) do not help with Varroa control or honey production.  Of course, knowing him, Aaron accurately presented Calderone's summation and conclusions.  That said, I have a great deal of doubt whether Calderone's conclusions are the last word.

First, concerning honey production.  I am a firm believer that "high" ventilation here in a temperate climate results in higher honey production than otherwise.  What is high ventilation?  OMB does not necessarily result in high ventilation.  My hives have OMB and an extra 3/8" opening in the front of the hive above the top super.  By themselves (with no extra top opening), OMB would not (it seems to me) result in much, if any, extra ventilation compared to a solid bottom board.  We do not know from Dr. Calderone's talk whether there was any extra top ventilation.  Peter, can you share that with us?

Many respected researchers come to different conclusions than Calderone when it comes to the role of OMB in Varroa control.  In this months issue of American Beekeeping Journal there are several papers published that were presented at a meeting of honeybee researchers earlier this year.  Several  of such papers report superior Varroa control with OMB, combined with other concurrent actions/non-chemical treatment(s).  Unfortunately, my copy is home so I cannot quote specifics, but perhaps someone else will share those with the list.

Are we to assume that Calderone is wrong and others right...or vice versa?  I don't think it is that simple.  OMB are meant to be one of several means to be applied to reduce the requirement for chemical treatment, not to eliminate Varroa.  Thus the term "control" of Varroa.  While Calderone's data do not indicate benefit, I personally choose to believe that they are of significant benefit...under certain circumstances.

Best of all, they are cheap and lightweight and certainly do no harm.  To me, their widespread use is one of the truly significant beekeeping changes in the past 30+ years...even though some have used them for almost 100 years!

On another subject, Calderone also reported on the benefits of freezing drone brood to control mites.  In this case, the Varroa reduction was nothing short of astounding!  When I asked "Do you think that controlling Varroa through freezing drone brood will ever be practical for commercial beekeepers", his reply was "ABSOLUTELY, no", with just that emphasis.  He did state that it should be practical for up to 20 or so hives.  This involves freezing 4 times a season.

I have just about 100 hives and in 2001 I froze two frames of drone brood per hive (same as Calderone), a total of two times per hive and felt I should have frozen it three times (but my drone foundation had to be drawn).  My Varroa counts in August/September were negligible and most hives did not receive a fall treatment.  My fingers are firmly crossed waiting for spring results.   

Lloyd
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http://www.rossrounds.com
Lloyd Spear, Owner of Ross Rounds, Inc.
Manufacturer of round comb honey equipment and Sundance pollen traps