> Examination of floor debris can give useful clues as to what's 
happening overhead including evidence of bees damaging 
mites or aborting afflicted pupae.

So I have been finding lately.  Instead of lifting a lid and pulling 
frames, one can learn to interpret what is landing on the drop 
board.  There is a learning curve, and like any method of 
observing bees, there is a learning curve and patience is required.

This method of observation is almost entirely non-invasive and very 
instructive.

The hive bottom can be left either closed or open, simply by inserting
or not inserting a board.

I agree with Peter, though that counting on open bottoms for mite 
control could lead to disappointment.

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