http://forum.honeyflow.com/t/varroa-mites-and-treating-with-oav/9682
Hi Judy, so sorry about your colony. Same happened to me, because I applied an effective treatment in an ineffective manner. Unfortunately varroa mites have raised the bee survival bar very high in so many parts of the world. There may be some evidence that oils work, but I havent found any very convincing methods using them. Dawn & Dee know what they’re talking about - and the link above posted by Logan gives a great overview of the problem along with a specific oxalic acid treatment timetable. Performing mite counts and oxalic acid vapor treatments are not very difficult at all, and you’ll get plenty of help & guidance here. But please see if you can find someone with experience in your area too - very often your methods need to be modified to suit your local climate & people here may not have exact enough knowledge of that.
Good luck 
