To keep your honey bee colonies healthy, it is important to determine the level of varroa mites in your colonies. This method provides a good estimate of the number of varroa mites on the adult bees. This method has the advantage of not killing the bees.
If you know how many bees were in your sample, you can estimate the number of mites per 100 bees. If there is brood in the colony when you sample, you should double this number to factor in the amount of mites in worker brood. For example, if there are 5 mites / 100 bees, the total infestation is probably 10 mites/100 bees. If your colony has over 10-12 mites/100 bees, you should consider treatment.
Follow these 10 easy steps to determine the infestation level of varroa mites in a honey bee colony.
1. The first step is to make a container with a cover made of 8x8 hardware cloth. An easy method is to use a wide-mouth canning jar. Use a ring type cover. Cut a circle of 8x8 hardware cloth the size of the cover that fits in the ring and use it instead of the cover.
2. You will also need something white to shake the mites and powdered sugar into. You can just shake them onto a piece of paper if it is not windy. A white container works best but any light color (yellow) would be ok.
3. Shake about 200-400 bees into the container. You can shake the bees from a frame into a bent piece of sheet metal (flashing) to help pour them into the container.
4. 1 fluid oz. = approximately 100 bees. 1/4 cup = approximately 200 bees. You will have to shake the bees in, then tap the bottom of the container to get all the bees on the bottom of the container to measure them.
5. With the bees in the container place the 8x8 screen on top and secure.
6. Put about 2 Tablespoons of powdered sugar into container. Shake the bees with the powdered sugar until they are well coated. Let the container sit for about 1-2 minutes.
7. Tip the container upside down over the white container and shake the powdered sugar and mites out through the screen.
8. Continue to shake for at least one minute to be sure you have all of the mites.
9. Count the number of mites in the powdered sugar. If you have trouble seeing them you can add a small amount of water to dissolve the sugar, making the mites easier to see.
10. Return the bees to their colony.The bees will survive. Once they are cleaned up they can go back to work.
University of Minnesota Instructional Poster #155, Gary S. Reuter and Marla Spivak, Department of Entomology
Download the original Powder Sugar Roll for Varroa Sampling .pdf here.