It is all I use. I have a package of Hopguard left, but am sure it is expired by now.
I tried OAV after a LOT of reading.. and no one seems to know exactly how it kills the mites. In most reports and tests they claim that "observation would suggest" that the crystals penetrate the mites soft parts and the acidity kills them, at least with vaporization..
A quote from Randy Olivers Site at;
http://scientificbeekeeping.com/oxalic-acid-questions-answers-and-more-questions-part-1-of-2-parts/OK, so OA spreads and kills by contact—that’s why heat vaporization (to be covered in the next installment) works well. We still don’t know how it gets into the mite’s body (no one’s proposing that mites crawl around licking the stuff up). We do know that oxalates in plants form spiky crystals that can penetrate animal tissue, similar to those of boric acid (commonly used for cockroach and ant control). Boric acid forms abrasive spikes that can penetrate the soft integument at the joints of the insect exoskeleton, and apparently desiccate the insect. It also acts as a stomach poison to ants.
Could oxalic acid work in the same manner? Heat vaporized OA does form tiny spiky crystals, as does OA evaporated from a water solution.
End Quote
this seems to be the general consensus, and as such, the only way varroa could become resistant or immune would be if they grew hardened plates over their soft joints.. which, would render them immobile...
If you read the site, you will read about how organic OA is, and how many common plants etc it can be found in, including natural honey from hives that are not treated with OA dribble or OA vapor.
So after a lot of looking and reading, I decided to try it...
All I can say is.. WOW!
If the effectiveness in treatments continues, I will continue to use it. No resistance has been reported from the countries that have been using it for some time with excellent results.
The dribble method does have some drawbacks and effect on the bees, and the vapor method has its dangers to the beekeeper if they were to stick a hose in the hive and try to breathe the stuff while treating.
I have always made sure I was well clear and upwind when treating, though I have been told that if you were to breathe it, you would close up and start coughing long before you could inhale a dangerous amount. I really don't care to test it.
No harmful residue to the bees the wax or the honey. In one test they treated weekly for something like six months, with no adverse effect on the bees, but they did say they could not find any mites in the hive at all at the end of the test.
"I have hope, that one day it will be approved for use here in the US.. but until someone puts up a lot of money and time to get it apporved, it will likely remain a method of bleaching the wood frames of your hives.
I have a vid and other info on my site if your interested.
http://outyard.weebly.com/treatments.html