Two or three members of this list asked where researchers from Cornell had
published their data on screen bottom boards.  Peter Borst seemed to avoid
answering the question, although he is employed by the principal researcher,
Nick Calderone, and did considerable grunt work in Calderone's assessment of
the efficacy of screen bottoms.

At our last New York State meeting (December, 2001 ?), Dr. Calderone
provided a verbal report.  To the best of my knowledge, and I watch for such
things, no paper or article has been presented.  However, Dr. Calderone is
extremely well respected and I am inclined to believe that the lack of a
written report is due more to the press of other work than it is to any
hesitation concerning the data or methodology.

Bluntly,  I recall Calderone said he could not find any relationship between
the use of screen bottom boards and Varroa populations or honey production.
However, I do not recall Calderone saying that screen bottom boards
increased Varroa, or decreased honey production.

The first reference I recall that screen bottom boards might be used for
control of Varroa was in 1999, by Shimanuki and Pettis (ABJ 143(6):
471-473).  They demonstrated that colonies with screen bottoms had
significantly fewer Varroa early in the season than did colonies on solid
bottoms.  However, later in the season Varroa populations caught up with
those on bees in hives with solid bottoms.  Shimanuki and Pettis speculated
that screen bottoms might be very useful as part of an IPM program, but said
they could not be relied upon as a sole means of control.   Since, their
conclusions have been repeated by several other researchers, most notably
Sammataro.

So, while Peter Borst is correct in stating that no researcher has stated
that screen bottoms can be used as a sole control, several continue to be of
the view that they will be useful as part of an IPM strategy.

Until recently, my personal view has been "why would anyone use a solid
board"?  I have never seen any indication that use of a solid board is of
benefit when compared with use of a screen board.  Moreover, a solid board
is considerably more expensive and heavier than a screen board, and hives on
screen boards (with proper upper ventilation) never develop the large bee
beards commonly seen in hot weather.   I have converted almost all my hives
to screen boards.

As reported a couple of weeks ago, new research in Canada has demonstrated
a downside to screen boards.  Apparently Varroa is much more sensitive to
high temperatures than are honey bees, and that accounts for the fact that
Varroa is not a significant problem in tropic climates.  Since screen boards
reduce hive temperatures, the Canadian researchers apparently conclude that
they actually promote Varroa reproduction!  (This could account for
Shimanuki's and Pettis's observations that while screen boards initially
have a significant effect on reducing Varroa populations, by the end of a
honey season Varroa populations in hives with screen bottoms are equal to
those in hives with solid bottoms.)

Personally, I am keeping my solid bottoms but putting all new hives on
screens and advising those making initial purchases to buy screens only.

Lloyd
Lloyd Spear, Owner of Ross Rounds, manufacturer of comb honey equipment
for beekeepers and Sundance pollen traps.
http://www.rossrounds.com
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