A number of years ago, a method of non-lethal testing for varroa mites on honey bees was developed at the University of Nebraska by entomology professor Dr. Marion Ellis and some of his students. It involved the use of powder sugar in a dust application. They found that when honey bees infested with varroa mites are dusted with a coating of powdered sugar, many of the mites fall off – perhaps as a result of increased grooming by the bees, or maybe because the sugar makes it more difficult for the mites to maintain their grip. Various substances could be used instead, but powdered sugar works well, is cheap and readily available, and is easy for the bees to clean off.
The powdered sugar roll, as it is called, has become a common technique for estimating varroa numbers from a sample of bees. It is similar to an alcohol wash – an alternative method which I often employ with beekeepers in the field. However, an alcohol wash kills the bees in the sample (which bothers some beekeepers), and great care must be taken to ensure that the queen is not among them. After treatment with sugar, the bees are returned to the hive unharmed. Directions for using the powdered sugar roll to test for varroa can be found in a 2000 University of Nebraska apiculture newsletter. A most important part of the procedure is that the bees placed in the jar receive a thorough coating – see the link.
The efficacy of the powdered sugar roll in dislodging mites to monitor their numbers led the folks at the University of Nebraska to wonder if it could also be used as a method of varroa control. Several years of research followed. A 2005 study showed some knockdown of varroa using powdered sugar. To make sure that all the bees in a colony were treated, a special screened box was constructed and attached to the hive entrance. All of the bees were forced into the box by means of a bee repellant (Bee Go) and, once there, were carefully dusted with sugar. Even with these extra measures to achieve thoroughness, the results were mixed, and the folks at Nebraska concluded that controlling varroa with powdered sugar was not practical. Several subsequent studies at other research institutions have reached the same conclusion.
Move forward to the last few years. I’m often contacted by beekeepers who have lost colonies. The first question I always ask is, “Do you monitor for varroa mites, and how do you treat for them?” All too often, the response I get is that they used powdered sugar as a control method (meaning they sprinkled it between the frames of the hive), and that they did not monitor after applications because they were confident that the sugar would work. Now their bees are dead, and they are looking for the cause. I have long questioned the effectiveness of the powdered sugar method for varroa control. I do not tell beekeepers who believe in it not to use it, but I stress that it is IMPERATIVE to monitor both before and after applications (using sticky boards is one good way), and to combine it with other control methods as necessary. Dusting with powdered sugar will certainly knock off some mites, but the question is, “How many are left, and are there enough still in the hive to threaten the health of the colony?” Only monitoring can give that answer.
If you using or are contemplating using powdered sugar for varroa mite control, I urge you to read Jennifer Berry’s recent article in Bee Culture magazine (January issue, page 23), Revisiting Powdered Sugar For Varroa Control on Honey Bees. This article summarizes past varroa control research with powdered sugar as well as recent work at the University of Georgia. Researchers there found that, while powdered sugar resulted in some varroa’s falling off the bees, colony losses for hives treated with powdered sugar was about the same as for untreated control hives – nearly 40 percent.