How does a beekeeper know if their bees have a varroa mite problem?
It is not possible to accurately assess the varroa mite population within a hive by eyesight alone. The varroa mite wash is therefore an important diagnostic tool for the beekeeper. It will tell you the number of varroa mites per 300 bees in your colony, which should guide your decision about treatment.
A simple method for conducting the varroa mite wash uses the following pieces of equipment: 2 clear plastic 16oz cups with lids, a 12-inch square of mesh fabric, 1 tablespoon of Dawn Ultra dish soap, 1⁄2 gallon of water, a 1⁄2 cup measuring cup, and a dishpan. The mesh fabric needs to have spaces within it that are small enough to retain worker bees and large enough for varroa mites to pass through. Varroa mites are about the size of a pinhead.
Begin by mixing one tablespoon of dish soap in 1⁄2 gallon of water. Cut the bottom 3⁄4 of an inch off one of the clear plastic cups. If you use a hot knife to do this, the edge will not be as sharp. Place the mesh inside of the uncut cup and the cut cup inside of the mesh. Fill this combined cup about 3⁄4 full with the dish soap and water mixture. Keep the lid available nearby.
You will be pouring a 1⁄2 cup of bees into this cup and swirling them around. As you swirl for about a minute, the varroa mites that had been clinging onto their bodies will fall to the bottom of the cup. Looking upwards at the bottom of the cup, you can count the number of mites that you see. Varroa mites are reddish and the size of a pinhead.
To gather a 1⁄2 cup of bees, take a brood frame from the outer edge of the brood nest. Shake the bees on that frame into your dishpan. The older forager bees will quickly fly away, leaving you with young nurse bees in the dishpan. As the nurse bees disperse to form a single layer in the dishpan, look for the queen. If the queen is in the dishpan, be sure to get her back into the hive right away.
Tilt the dishpan and tap it so that these nurse bees clump into something like a pile. Then, carefully scoop them up in your 1⁄2 cup measuring cup. If the cup is overfull, then brush the overflow off. Pour this 1⁄2 cup of bees quickly into your plastic cup with the dish soap mixture and put its lid on.
Pickup this plastic cup and begin slowly swirling it around in a small circle with the palm of your hand on the lid. After about a minute all the varroa mites on your bees will have fallen through the mesh to the bottom of the plastic cup. Now remove the mesh along with the inner cup so that all you have left is the outer cup with the dish soap mixture and the varroa mites at the bottom. Count these mites. If you count more than 5 mites, then you should treat this hive for varroa mites.