> studies to compare the effectiveness with and without screened bottoms of,

> say, formic acid or fluvalinate?

Another thing of interest (as touched upon by Peter's comments) would be the
condition of the fallen mites in the control hives.  Are they old and
decrepid or beaten up by grooming bees and on their way out anyway, or are
they lively, verile mites that you'd be glad to have fall out of your hive?

Although screened boards aren't as promising as they first appeared, there
is a lot that is still unknown about this possible useful tool in an IPM
program.

Aaron Morris - thinking the more we know, the more there is that we don't
know!