Sugar rolls are a non-lethal way to determine the varroa mite infestation rate on a subset of the adult bees within a colony. Test results allow you to compare the infestation rate with published thresholds and make decisions about whether or not treatment is warranted.
It’s a good idea to do sugar rolls monthly throughout the entire bee-working season to make sure mite levels remain below economic thresholds and to plan ahead for treatment opportunities. It’s also a smart idea to do a post-treatment sugar roll approximately 10-14 days afterward to verify that the treatment was effective.
The keys to getting accurate data when doing sugar rolls are consistent sampling methods and the correct rolling/resting/shaking technique.
Because the actionable levels of infestation (e.g. when treatment is needed to protect the colony from harm) are quite low - only 2 or 3% - a particular subset of the bees in the colony is chosen to act as surrogates for all the adults. The bees with the highest infestation rate are the young nurse bees occupied tending the brood. Phoretic-state varroa mites congregate on the bees working near the open brood so that they can easily enter a mature larva’s cell before it is capped.
To maintain the accuracy of the test, it’s important to choose the bees to be sampled correctly and consistently, both as to the location they are taken from, and the number of bees in the test sample. The methods described below will help you do that.
Doing sugar rolls regularly throughout the season will improve your skill in collecting the sample and performing the test accurately. It may seem a bit awkward at first, but with experience it will become faster and easier, and a routine part of your hive management skills.
These items can be purchased as a Varroa Sugar Roll Kit, or assembled on your own from household items.
One important note to start out: Although this is a non-lethal test, it’s important to be able to find your queen and make sure she isn’t among the bees being tested. If you cannot be certain that you will be able to spot your queen, select a frame away from the brood nest and adjust the test results upward by 20%.
The type of adult bees with the greatest number of mites on their bodies is likely to be the nurse bees caring for the open brood. Those are the bees you want to test. Select a frame that is the first one just outside of the brood area. Look it over very closely to make sure the queen is not on it.
Set the plastic tub on the ground near the stack. Hold the selected frame firmly and give it a sharp downward shake directly over the tub. This will dislodge the bees and drop them, unharmed, into the box. The nurse bees, unlike the foragers and drones, will stay in the tub for a short period. As soon as the bees are off the frame, put it back into the hive to keep the brood warm and safe.
This is a critical step in achieving a high level of test accuracy. A precise and consistent sample size (the number of bees actually tested) is the key to getting very reliable data from the test, so take some care with this step.
First, consolidate the bees in the plastic tub by giving one corner a sharp thump on the ground. This will drop all the bees down into that corner of the box.
Then, if using a commercial jar without markings, use the half-cup measuring scoop to gather up bees from the plastic tub and dump them into the jar. Cover the jar with the screen top.
If using a jar with the one-half cup amount marked on it, set the jar on top of the frames and pour the bees in the tub directly into it. Cover the jar with the screened lid. Any spillover during the pouring will fall harmlessly down into the hive. When working with a marked jar, you can bang the jar on the palm of your hand to drop all the crawlers down into the bottom to check if the quantity of bees in the jar matches the line.
Accuracy at this stage of the test is very important. Over time you will get much better at judging the right quantity amidst the swirling bees. When you are confident that you’ve got the correct amount of bees in the jar, screw the lid on. Dump any extra bees still in the plastic tub back down into the hive.
Scoop a heaping hive-tool tip quantity of powdered sugar on to the screen lid and use the hive tool to work it down through the screen.
Roll the jar briskly but smoothly around in your hands, using both hands to keep it moving, for 2 minutes. Keep the jar at an angle off of straight upright in order to increase the exposure of the bees to sugar.
Once the rolling step is done, set the jar aside to rest in a shady place for 2 minutes.
While the jar is resting, spread white paper towels on the bottom of the plastic tub. You want to have a clean surface to make seeing the mites easy.After the 2 minute rest, invert the jar over the plastic tub and shake it vigorously for 2 minutes to get all the powdered sugar, and any mites, through the screen and out of the jar.
After that, just open the jar and dump the test bees back in the center of the hive on the top of the frames. The other bees will clean them and remove the sugar.
You don't have to count the mites immediately. They're not going anywhere, so finish getting the hive closed up.
Once the hive is closed, use the water spritzer to spray water on the sugar that was shaken out into the plastic tub. The water will melt the sugar and the mites will be revealed. Count all the mites you see, using a magnifying glass, if needed.
Once you have counted all the mites revealed in the tub, divide that number by 3. The result is your infestation rate percentage. You divide by 3 because a carefully measured, half-cup sample contains approximately 300 bees.
Although some beekeepers will allow a 3% infestation rate (9 mites revealed after the test), here at Betterbee we consider the treatment threshold to be 2% (no more than six mites per 300 bees). Over time, you will develop your own thresholds based on the success of your hives, but 2% is a good starting point. We use the Ontario Tech Transfer Team Mite Thresholds.
Remember, if you used a frame away from the immediate brood nest in order to reduce the chances of testing your queen, you need to adjust the results upward by 20%. That means if you saw, for example, 5 mites, you should count that as seeing 6 mites.