Scott said "In addition to chemical control, many beekeepers are using an 8
mesh
screen above the bottom board to reduce the number of mites.  In fact, our
state entomologist reported to the club that there was a 40-50 percent
reduction in mites using just the screen, with no chemicals at all."

In the June, 1999 issue of American Bee Journal, Pettis and Shimanuki
presented a paper that reported an early season 25% reduction in varroa
(compared to control hives) by using solely an open-mesh screen.  However,
by late summer there were no differences in varroa populations in hives with
and without a screen.

This is very good news as the implication is that it might be able to avoid
spring use of Apistan and treat just once a year, in early fall.

The theory of the open-mesh screen is that there is a normal and on-going
mite fall.  This has been documented for many years by use of sticky boards,
without mite treatment to cause their fall.  Presumably the mites just lose
their grip or are picked up and dropped by the bees.  My understanding is
that after falling, mites have been observed to crawl back on passing bees
and thus get back up into the brood nest.

In constructing a screen, it is very important to use a mesh size that mites
can get through but bees cannot.  Eight mesh to the inch (1/8") or 3/5mm
mesh will do the job.

In the US an inexpensive mesh that is constructed to fit on top of a normal
bottom board is being sold by Betterbee (800-632-3379) and Brushy Mountain
(800-233-7929).  I understand that this somehow redirects the bees into the
hive, without them having access to the bottom board.  However, unless the
beekeeper has sticky paper (sprayed with food oil (Pam) or something
similar) to trap the mites, they are likely to find a way to catch a ride on
incoming bees.

Other beekeepers have attached the screen to the bottom of the hive,
eliminated the bottom board, and reported good success (private
communication).  Obviously, in this case an upper entrance has been provided
for the bees.  In one case this was as simple as setting the top of two hive
bodies used for the brood nest back about one inch (13mm).  This beekeeper
leaves the setup this way (no bottom board, an eight mesh screen stapled to
the bottom of the hive, and the top hive body set back from the bottom by an
inch) all winter.

I personally think that some type of a screen to let mites fall and treating
just once a year is the way to go.  However, I think those that try this and
do not have a way to prevent the mites from crawling to where they can catch
a bee will be disappointed with the results.

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