Karen,
I'm somewhat against prophylactic treatment. However, especially in the winter, in my opinion, the mites are worse than a treatment is, and the downsides for OA treatment are pretty minor. Second most important is to check the mite levels after the treatment to see what they are. You could treat with OA, either drizzle or vapor pretty quickly, then do another count at the first warm day. As always though, I believe the best resource is the HBHC tools for Varroa management.
Allen Engle
