I will reiterate what is already said. It is the chemicals like fluvalinate and coumaphos (also another one called Amitraz) (these are pesticides) that are causing mites resistance to chemicals.
Oxalic acid and formic acid and Tymol (Apiguard) do not fall into these categories of chemicals (pesticides).
A quote from the MiteGone "Formic Acid Use Handbook anad Manual of Treatments" follows: Read closely
"WHAT LEVEL OF EFFICACY IS SUFFICIENT WITH NATURAL SUBSTANCES?
More and more scientists are advising beekeepers that it is not necessary to kill everything at nce with 100% efficacy as pesticides originally did.
Pesticides act on a narrow band of nerve genes that easily mutate and mites build resistance quickly. 100% resistance to fluvalinate and coumaphos and 80% resistance to Amitraz was found in Florida in December 2001. Scientists are advising beekeepers to use natural substances like Tymol, formic acid and oxalic acid, which depending on application, have 70-100% efficacy. Since natural substances act on a very wide spectrum of genes from respiration, reproduction, and skin, mites are very unlikely to build resistance quickly. A treatment with 70% efficacy used twice a year can keep mites below the economic damage threshold.Keep mites below the 8-10 mite natural drop.
A low presence of mites may also allow bees to build up resistance to mites by increasing bee grooming and building natural defences against mites. All of Brazil has a natural selection population of bees and mites that exist together. Brazilian beekeepers do not treat. Unfortunately, having 90% of colonies dies through natural selection is not an option in North America."
If you want some very interesting reading about mites and mite controls, I have suggested in prior posts cited a site (ha, ha), I will post it again.
Today, is a glumb day. I am inserting the sticky boards into my colonies to ascertain mite levels. I did two sugar shake treatments at the beginning of the season, I have done no further treatments since that time. I began with (4) five frame nucs and (4) package bee colonies at the beginning of May. These colonies came to me and had had had formic acid treatments done in the original colonies in the spring. So, evidently, they came to me clean. They were not 100% clean by the time that I had done the sugar treatments, but the mite counts were very, very low. So....in a few days, the sticky boards, after 72 hours in the hive, and the time to count the mites will tell me where I am presently at, and what treatment is required, or not. I suspect treatment will be required.
The MiteGone site is listed below. The owner of the MiteGone is Bill Ruzika, he lives in a town about 400 km to the northeast of where I live. He travels worldwide teaching about the importance of keeping bees at a livable mite level count. I trust this man.
Now, going back to the small cell, as so many beekeepers do. They are obviously doing excellent with mite levels. This has been made known over and over again on our forum, and it sounds like Dee Lusby runs alot of colonies on smal cell and can absolutely condone smal cell beekeeping, and this is good that it is working for them. Yeah!!!!! If anything, read the information on this site, just to be an informed beekeeping person.http://www.mitegone.com/
Have a wonderful day, greatest of this beautiful life. Cindi