I think all beekeepers can now agree that Varroa mites are a threat to honey bees. They reproduce at a phenomenal rate and spread diseases like Deformed Wing Virus. There are many schools of thought on how to treat, but an important step, no matter what treatment method you prefer, is to know the ratio of mites to bees. It’s not difficult to assess and takes less than 10 minutes. Watch my video on how to do a sugar roll.
Just looking at your bees is insufficient. A sugar roll is not difficult and doesn’t take very long. You can do it once a season during a routine inspection. You just need a few supplies: a plastic tub with lid, a large-mouth quart Mason jar with a screened lid (use #8 screen), a spray bottle of water, a white paper plate, a timer, and some powdered sugar.
Collect a sample of bees: Select a brood frame with plenty of bees. If the queen is on the frame, either select another frame or carefully move her to another frame. With a sharp rap, knock the bees into the plastic tub and put the lid on. Put the frame back in the hive and move the tub of bees to your work area.
Roll with sugar: Open the tub of bees, scoop one-half cup, and pour them into the Mason jar. Screw on the screened lid. You may set the tub of remaining bees near the hive. Put 2 tablespoons powdered sugar through the screened lid of the jar. Vigorously shake the bees for 1 minute, then set down the jar for 3 minutes. After shaking and waiting, invert the jar over the paper plate and shake like a salt shaker until no mites are falling out. Add another tablespoon of sugar to the jar, shake for 30 seconds and let the jar sit for 2-3 minutes. Shake out mites over the plate until no further mites fall out.
Count mites and assess percentage: Spray the paper plate with water to make the mites more visible. To calculate the mites per 100 bees, divide the number of mites you count by 300 (ex: 12 mites / 300 = .04) then multiply by 100 (0.04 x 100 = 4). If you counted 12 mites, your mite percentage for that hive is 4%. If you have a mite count of 2% or greater, you need to treat.
The Honey Bee Health Coalition has a free download on management tools.