I've used apivar for several years with OAV. Apivar has done a good job and I've used OAV to clean up in winter and early spring just to stay ahead of the mites. I was shocked this year when I did a post Apivar mite wash. Six mites 2 weeks after a 45 day treatment. I had this in 5 or 6 mites in 4 hives and 3 in two more with a half cup of bees measured out. All hives were treated with the recommended dosage of strips per frame of bees. All Apivar was well within expiration date. Posting for others. I'm off to plan "B" which is OAV and Apigurad.