I have used an oxalic vaporizer for several years for varroa control. I have also lost more than 50% of my hives over that period. I have never seen a drop-off of dead varroa after vapor treatment like I did with Apigard and other chemical treatments. Has anyone who uses oxalic vapor seen where it actually killed mites and had a drop-off on a tray under the screened bottom board? Has anyone had a problem losing queens when using oxalic acid vapor? Thanks, Jim