Evaluating the Varroa population using a screened bottom board
About 10 percent to 15 percent of Varroa mites routinely fall off the bees and drop to the bottom board. But if you use a screened bottom board (sometimes called a “sticky” board), the mites fall through the screen and onto a removable tacky white board. When this white board is in place, mites fall through the screen and become stuck to the sheet (you apply a thin film of petroleum jelly or a cooking spray to the sheet to help the mites stick). Just insert the sheet for a day or two and then remove it to count the mites. If the number of mites is more than 50, then appropriate control measures should be taken. A screened bottom board is also an excellent way to improve ventilation in the hive.
Knowing how to control Varroa mite problems
A number of products and techniques are available that help reduce or even eliminate Varroa mites populations. Here are the ones that I suggest you consider and a few that I think you should avoid as a new beekeeper. In recent years, it is a generally accepted practice not to medicate your bees unless you know it is necessary. Medicating your bees as a protective measure can actually diminish the effectiveness of medication when you absolutely, positively need it. The mites can build a resistance when medications are used too frequently.
There are a few effective and approved miticides (chemicals that kill mites). One is fluvalinate, which is sold under the brand name, Apistan, and is available from your beekeeping supplier. Another is coumaphos (marketed as CheckMite+). Formic Acid is also used as a treatment for tracheal mites (sold in gel packs under the brand name Miteaway II). In addition there are “soft” (safer) chemicals such as thymol (marketed as Apiguard). When any of the detection techniques mentioned earlier in this chapter indicate Varroa mites, you must immediately treat with one of these treatments by carefully following the directions on the package. Because Varroa mites can develop a resistance to these medications, it is prudent to alternate between two or more of these from one season to the next.
From : “Beekeeping For Dummies” By Howland Blackiston.