Varroa Mite Monitoring
Using a sugar roll to identify populations of Varroa destructor in honey bee colonies
MEGHAN MILBRATH, MICHIGAN STATE UNIVERSITY EXTENSION, JANUARY 2018
All photos in this document were taken by Andrew Potter (www.andrewpotterphoto.com)
Plan to monitor for mites at least once each month during the bee season. You may want to check more frequently in late summer, when risk is higher. If you have fewer than 8 hives, or want hive specific data, test them all. If you want to know the risk of the yard, check at least 8 hives.
Step 1. Get all your materials ready- make sure they are all clean and dry
Pick a hive, and make sure you have the following equipment, or your mite-check kit. To purchase a mite check kit, visit www.pollinators.msu.edu/mite-check. Instructions to make your own sugar roll jar can be found at the Bee Informed website.
- Powdered sugar
- ½ cup measuring cup marked at 100ml or 0.42 cups
- Container with white bottom
- Sugar roll jar
- A buddy isn’t necessary, but a second pair of hands often helps.
Step 2. Find a frame of brood.
Take the lid off of your jar. Open the colony, and move down through the colony until you reach the brood nest. Don’t use a ton of smoke if you plan to sample – you don’t want the bees to be running around.
You need a frame that has bee bread or brood - this is where you will find nurse bees. The nurse bees will have the greatest number of mites. Try to always select the same type of frame. This one (see above) has a lot of drone brood, so it may give us a different result. We try to choose a frame of brood with a mix of open larvae and capped brood, but as long as there is bee bread you should be fine.
This frame looks great. Check it carefully to make sure that the queen is not on it!
Step 3. Get a 1/2 cup of bees.
There are two ways to do this:
Method 1 - In the first method, you can knock the bees off the frame into your tub. Use one quick, hard shake – you want to go hard enough to startle them so they fall. Nurse bees don’t really fly, so they cling to the frames. You may have to shake more than one frame to get ½ cup in the tub. Don’t worry if bees fly up out of the container – these are older bees, and you are after the nurse bees.
Shake the bees to a corner of the tub. Gently scoop the bees into the cup. Make sure you have as close to ½ of bees as possible. Put the bees into the jar, and screw on the lid.
Method 2 - The second method sampling is useful when the frame has nectar on it – in the shaking method, the nectar can drip on the bees, making them sticky, which will throw off your counts. Method 2 involves slowly running the edge of the measuring cup along the frame, and letting the bees drop into the cup. You can move the cup either up or down. In the method shown here, you want to be very careful that you are gently tripping the bees into the cup, and not rolling over their bodies.
Once you have ½ cup of bees in the jar, put on the screened lid.
Step 4. Add powdered sugar.
Add a heaping hive tool of powdered sugar through the screen (about 2 tbsp). Make sure that the powdered sugar coats all the bees. Don’t worry about being exact here – you aren’t baking. The goal is to have enough sugar so the bees are well coated.
Step 5. Roll.
Roll the jar gently, making sure that the bees are sufficiently coated with sugar. Make sure that you don’t tip the jar upside down, and that all the mites stay in the jar until you can count them.
Step 6. Rest.
Set the jar in the shade for 2 minutes. While the bees are in the jar, they heat up, causing the mites to fall off. The powdered sugar prevents them from being able to crawl back onto the bees.
While you wait, you can put the colony back together.
Step 7. Shake.
After at least 2 minutes are up, it is time to shake the mites into the tub. Shake the jar over for 1 minute, shaking hard enough that you dislodge any mites that are stuck to the sides of the jar or in between the bees. A common mistake is to not shake vigorously enough, so make sure you put some effort into it!
Once all the mites are in the tub, you can return the bees from the jar to the hive. They will be a bit worse for wear, but the other workers will quickly clean them up.
Note that these bees still look dry and sugar covered. If your bees look wet, then you may want to repeat the trial.
Step 8. Count mites.
Add some water to the tub, dissolving the sugar so that you can see the mites.
Count and record the number of mites in the tub. A magnifying glass can be useful to see the mites, as they are quite small. Make sure that you are clear on what varroa mites look like. Here, the speck that is pointed out is a varroa mite. The similarly sized speck to the left, however, is not.
Calculate the number of mites per 100 bees. Your sample contains about 300 bees, so you have to divide the number of mites in your tub by 3 to get percent infestation. This colony had only two mites, so the mites / 100 bees=2/3.
Step 9. Compare your mite count to your threshold.
As of spring 2018, many experts are using a threshold of 3% infestation (3 mites / 100 bees, or 9 mites in your ½ cup sample). This number may change over time, or by region. Make sure that you check with other beekeepers, extension, and tech transfer teams to learn current thresholds.
Continue to test the rest of the colonies in your yard. If you have only a few colonies, you will want to test all of them. If you have a lot of colonies, test at least 8 in each yard. Make sure that you are prepared with a plan if you find even one colony with high levels of mites. A high mite load in one colony can quickly spread to others.
Congratulations! You have just finished monitoring your honey bee colonies for the varroa mite, the first step in ensuring that your honey bee colonies are kept safe from this terrible pest. If your mite populations are below threshold, take good notes, and enjoy your day. If your mite populations are above threshold, make sure that you take action to protect your bees. For useful documents on what tools to use to manage the varroa mite, visit: pollinators.msu.edu/resources/beekeepers/planning-for-varroa/
Sugar roll step-by-step
- Gather all your materials
- Find a frame of brood
- Collect a ½ cup of worker bees from the brood into your jar
- Add 2 tbsp powdered sugar to the bees in the jar
- Roll the jar to coat the bees with sugar
- Put the jar to rest in the shade for 2 minutes
- Shake the mites out of the jar into a tub
- Count the number of mites in your sample
- Divide by 3 to get the number of mites / 100, and compare to your threshold
- Feel good that you are helping keep your bees healthy!