I have hives in Mass and Conn. I had one case of PMS last year although
I didn't know it at the time, requeend and the colony was fine. I treated
with apistan on aug 15 of last year, noticed higher than normal level's
of mites in feb/march, waited for formic acid to become available and
treated with that this spring. I had never treated in the spring b/4.
  My first hive was noticed in early June, again i wasn't sure it was PMS.
requeened and eventuallly killed the hive. checked all hives in early july
and all appeared fine. went to put on apistan in mid august and one entire
apiary of 8 hives had crashed, esitimate of 10-20% of my other hives also
showed PMS but not as bad.  used checkmite on the 8 hives and used apistan
on the rest as I'm not registered to use it in conn, and am following up
with formic acid on the ones that i used apistan on. also doing a drop test
on some of the hives that i used apistan on.  since last year was
classified as a low mite year by the bee inspector in mass, I suspect that
the mites are getting/or are restistent to apistan, I'll definetly know in
the spring by the # of hives I lose. Since Formic acid didn't seem to do
anything when treated in the spring, and if you remember we had one of the
warmest springs in a long time, seems to me that the only alternative left
is to use check mite?                             mike bassett