David Ayres asked for experience with mesh floors as a means of combatting
varroa.
These are widely used in the UK, not as a method of trapping live mites
which drop of bees (negligable in terms of the total mite population of a
hive, I would think), but as a means of monitoring the level of infestation.
Studies by Dr Stephen Martin of the National Bee Unit, Central Science
Laboratory, York, UK, ([log in to unmask]) have shown a relationship
between natural mortality and total mite population. By counting the dead
mites dropping through the screen of the varroa floor, and multiplying by a
factor depending on the time of year it is possible to get a good estimate
of the total mite population of the hive. From this it is possible to say if
immediate treatment is necessary or if it is safe to postpone treatment eg
until after removing the honey crop. This work was carried out under UK
conditions, and I dont know if the same factors would apply in different
climates. I will try to get a reference to published data, if anyone is
interested.
With regard to the general effect of hives with open mesh floors, Helmut
Horn published observations on overwintering hives of this type compared
with conventional floors. An English translation by AE McArthur was
published in BEE CRAFT [72(7):201-210, 1990], as "Observations on the
Overwintering of Honeybee Colonies in Hives with Open and Solid
Floorboards".
Alistair Reid published a series of studies alone similar lines (Bee Craft
Feb 1991, Jan 1993, Feb 1994, Apr 1995 and Feb 1996). The key points seem to
me to be: use an insulated roof with no ventilation holes. warm air from the
cluster rises, moves to the outside of the hive, and drops down through the
floor taking excess moisture with it. Colonies are slower to start in the
spring, but quickly catch up and do well. Winter losses are less than the
solid floored hives, presumably due to the drier conditions. (Bee Craft
editor is Claire Waring [log in to unmask] ).
One problem with varroa floors is the increase in wax moth, as the bees are
unable to keep the floor clean. A combination of  the two concepts, putting
a tray under the mesh only when monitoring varroa gives the best of both
worlds. I've no idea about ants!
I am Editor of Gwenynwyr Cymru / The Welsh Beekeeper, and this is my first
contribution to bee-l. Hope it's useful and not too long.
John Burgess [log in to unmask]