Varroa Mite Monitoring
Updated November, 2018
Monitor so you know the level of varroa in your hives
Looking for varroa is not the same as monitoring for varroa - you could have a lot of varroa in your colony, but not actually see any mites when you inspect. This is a really important point that catches a lot of beekeepers. By the time you see mites, it is usually too late. Our goal is to keep varroa populations from taking over our bees, keeping them from getting ill in the first place.
The best way to monitor varroa mite populations is to use a sugar roll or alcohol wash, because these methods allow you to get a percent infestation. In both methods you take a known number of worker bees, dislodge the mites from them, and count the mites, calculating the mites per 100 bees (percent infestation). Mite drops on inspection boards, checking drone brood, or just looking do not give you a rate of infestation, so it is hard to know what to do with the information you get. Learn how to do an alcohol wash or a sugar roll, so you have information that can help you make decisions.
Do I really need to monitor? When should I start monitoring? What is the best way to monitor for varroa? How many hives in a yard should I monitor?
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The alcohol wash is like the sugar roll, in that it provides information about your varroa infestation in terms of mites/ 100 bees or percent infestation. This means that we can quickly get an understanding of the risk to our bees from varroa-associated viruses. The advantages of the alcohol wash over the sugar roll is that it is a bit faster. You do have to come to terms with sacrificing 300 bees each time. I was able to this knowing that I was ultimately taking care of the colony - my long-living animal. You can easily make the kits at home, buy various versions, and get plenty of instruction. The method is exactly the same as the sugar roll, but you don't have to wait the two minutes. Some resources are below.
Randy Oliver's page www.scientificbeekeeping.com has tons of resources on this. He has spent a lot of time perfecting this method so that it can be done at scale.
Understand the safe Threshold for varroa populations
Remember that your goal is to make sure that your bees are always healthy. This means we want to prevent varroa populations from reaching dangerous levels. Usually, the varroa population builds over the summer, peaking in late summer early fall. This means that there are times when we can find varroa in the hive, but it hasn’t yet reached a level where the life of the colony is at risk.
As of 2018, the general consensus is that < 3% infestation is safe.
In a standard sugar roll test or alcohol wash where you count 300 bees (100 ml or just under 1/2 cup), you should see less than 9 mites. Over time this number has gotten lower as the epidemic has worsened, so you may see higher thresholds listed in older documents. A safe level of 3% is a guideline, set because we often see signs of disease around 5%.
Keep in mind that this is still a LOT of mites. Let’s say you have 50,000 bees in your hive. A 3% infestation represents 1,500 mites on the adult bees. If even half of the mites are under the cappings, you would have 3,000 mites in your hive! (and that is considered safe!)
You can set your own threshold through experience - monitor your colonies (recording their levels and how they survive) and to talk to extension agents and local successful beekeepers in your area (who have <10% loss). If you consistently see that colonies with mite populations above a certain level do poorly, then that is your threshold. Be persistent, as thresholds can change over time as the mites or the viruses evolve. There are other factors to take into consideration: How far away are you from raising winter bees? Will you get a break in the brood cycle soon? How much season is left for varroa to grow? Northern beekeepers have to work hard to make sure varroa populations are low in the late summer/ early fall to protect winter bees, while beekeepers in warm climates might not be able to count on a break from population growth in the winter.