>>The problem with OA from the research I have done is keeping the hive below varroa threshold until the broodless period. This is true. I use this to my advantage to select breeder hives that can handle varroa loads from one fall to the next w/o any additional treatments to raise queens from the following spring. >>The second problem is figuring the exact kill you got is hard as many times it takes a couple weeks for varroa to die.\ I don't bother counting mites since I am sure of the method's efficacy (to my surprise, I don't see varroa in capped drone comb until the following September or so). I place 1" thick styrofoam, as winter insulation, under the screened bottoms in the late fall before the OA treatment. When I remove the styrofoam in the spring, I do see a lot of mites in the debris. >>Many beekeepers are going to OA alone. I believe you need to treat at least once with another treatment in our area. Apilife var and apiguard have been the most used treatments in our area. Another late-summer treatment may be needed in areas where very large bee populations are required to make it through very severe winters. In my area (zone 7, downstate NY), just the OA dribble seems to work fine. In some hives I will see PMS bees in October but the colonies don't collapse and winter fine. We do get several good days here in the winter for cleansing flights. Waldemar -- Visit www.honeybeeworld.com/bee-l for rules, FAQ and other info ---