Formic Acid is being used extensively in Canada where it is now legal. It has been used for several years in the U.S. illegally. Approval has been applied for by Mann Lake Supply. Liquid Formic is available from many chemical companies in the U. S. in 55 gallon drums for about $5.00 per gallon. The Canadians are using pads soaked in a 60% solution of formic and placed on the top bars. As I understand it, three treatments 6 days a part are required for tracheal mite and 6 treatments 6 days apart for Varroa. In my opinion, the this makes it cost prohibitive for a commercial beekeeper with a lot of out yards. The savings in material costs will be eaten up by labor and transportation costs. That is why I like the Nassenhof dispenser developed in Germany and available in the U.S. from Betterbee. It wicks the formic right in the center of the brood cluster and will last three weeks. It has been extensively tested in Germany but needs to be extensively tested in this country also to see how it works in the various weather conditions that exist in our country.