Before folks get too carried away with screened bottom boards, be aware that
researchers are finding that although they can be an effective tool to
combat varroa mites, they are NOT effective by themselves.  Although varroa
populations don't build up as quickly in a screened bottom board hive, by
the end of a season the varroa population will exceed the poorly defined
"economic threshold" and require additional treatment of some kind.
Screened bottom boards should be viewed as a tool in integrated pest
management.  They are NOT the end all for varroa mites.

For another view on Ed Lord's experiences with screened bottom boards,
especially as they pertain to varroa control, send a single line of mail to:
[log in to unmask]
that reads:
GETPOST BEE-L 025971