Rod wonders if he should treat again for mites, as he had a 20 mite fall
(with no Apistan) in 48 hours.

This also sounds to me as if it is a large drop.  Unfortunately, no one
knows the significance of any counted drop.  Moreover, the importance of a
20 mite drop in upstate NY (where I am) might not be at all important in
Missouri!  Have you tried your extension service for guidance?  Perhaps they
could put you in touch with someone at Missouri's ag school.

You are now at the mid-point between treatments.  However many mites are in
your hives, they will roughly double in number every 30 days.  Obviously,
things could get critical very fast.

Can you count on reasonably good temperatures for the next 28-40 days?  If
you can, I would treat now.  Don't worry about over-using Apistan, as it is
now a certainty that the formic acid gel pack will be available in the
spring and that should be rotated into your schedule.  Your bee supply
dealer will have it.

Hope this helps.

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