Varroa arrived in eastern Finland 30 years ago. It took 10 years to go over country. During few years we found Apistan resistant mites in many areas.
Beekeeping teachers have made hard work to get beekeepers use new chemicals. Methods have developed with others European countries. http://bees.freesuperhost.com/cgi-bin/yabb2/YaBB.pl?num=1136436349http://bees.freesuperhost.com/cgi-bin/yabb2/YaBB.pl?num=1136437131
It is going well now. Many beekeepers wonder where mites have vanishes. We have good situation because in winter we have good brood gap and it is easy to kill mites from bees' neck.
To meet too many mites in spring will still exist. Somethimes treatment has failed.
I have used now only oxalic acid trickling and this summer I have met under 10 mites in my 20 hives. I do not count them. I use drone larvae as cathers adn it is very difficult to find miten in drone cells. Next winter I use oxalic acid even I had one mite in my yard. I want to kill even it.
I need not worry about small cells or regressions or what ever with this system. I want big hives, big bees, big pasturesand big honey yields and few mites.