Hi John
 
Remember when you were in grade school and they gave you shots to make you
immune to various deseased.  Those shots were actually the virus itself in a
weakende state so that your body could develope a resistence to the desease.
 
Understanding that this works in humans, don't you think that it would also work
on bugs?  Most agree that Apistan starts to deteriorate from day one and after
approximately 45 days, it is starting to get weak enough to allow the mites to
develop resistance to it.
 
I have been using Apistan according to directions for quite sometime and to my
knowlege I have not lost any bees to voroa mites.  I have however lost some to
treachea mites.
 
I test reguraly during the honey flow and have on occasion removed a colony from
production to treat them.  This has worked well for me in the past and I expect
it will do so for some time to come.
 
Frank Humphrey