Detecting Varroa

The Powdered-Sugar Shake: Detecting Varroa Without Killing Bees

While seeking ways to recover varroa mites from bees for laboratory assays, Paula Macedo, a University of Nebraska Graduate Student, found a new way to check colonies for varroa that is more efficient than ether roll. In addition to being more efficient, it is not necessary to kill bees to conduct the test.

You will need the following:

  1. A wide mouth canning jar (quart or pint) with two-piece lid.

  2. #8 mesh hardware cloth (or any other mesh that will retain the bees while letting varroa pass through).

  3. Window screen (or any other fine mesh hardware cloth that will let powdered sugar pass through but retain varroa.

Retain the metal ring that comes with the two-piece lid, and discard the center portion. Cut a circle of #8 mesh hardware cloth to fit inside the ring. Collect 200-300 bees in a wide mouth pint or quart canning jar. Add powdered sugar to the jar through the #8 mesh lid (enough to coat the bees, 1 tsp. to 1 tbsp. should be adequate). Roll jar around to distribute the sugar. Allow the jar to sit for a few minutes while you collect additional samples. Then invert the jar and shake to recover the mites. The bees will remain in the jar, and the mites and sugar will pass through to a piece of paper. The sugar will make it difficult to count the mites. You can pour the sugar and mites into another jar with a fine mesh lid. Shake again and allow the sugar to escape. Then, dump the mites on a clean sheet of paper and count them. A brief shaking will usually recover 70% of the mites. If you persist a little longer you can recover 90%.

We can think of three possible reasons for the efficacy of this technique:

  1. Varroa mite legs have a sticky pad called the empodium that helps them adhere to their host. The presence of powdered sugar could make it difficult for mites to adhere.

  2. Powdered sugar stimulates the bees' grooming behaviour.

  3. The powdered sugar on the mite's body stimulates mites to release from feeding to groom themselves. Let us know how it works for you. It may be a problem in a windy Nebraska bee yard, but it works well in a lab.

Powdered sugar applied to a colony will dislodge a few mites from their host bees, but it is not highly efficient. Furthermore, the mites will eventually recover and return to their hosts. However, when bees are isolated from nest materials, the mite recovery from exposing them to powdered sugar is impressive. In fact, if you are willing to collect the adult population of a colony in jars and subject them to powdered sugar shaking, you can lower the mite infestation comparably to a chemical treatment. Continue shaking until mites cease to fall, and then return the bees to their colony unharmed. In future studies, we will examine the efficiency of the technique in bulk bee cages. One limitation to using this technique is that it is only efficient when brood is not present. When brood is present, 70 - 80% of the mites will be in sealed brood cells.