If you’ve already treated for Varroa destructor mites, you may think that you’re home-free and no longer need to keep doing mite counts. Unfortunately, we don’t recommend stopping. You should do mite counts after every treatment to confirm and make sure it was successful. Occasionally (though rarely) mite treatments fail or are only partially effective. It’s better to know that immediately — when you still have time to fix things.
Even more importantly, at some times during the year mites may still be coming into your hives daily. You need to know if mite populations are large enough to need more treatment. This is especially important in fall as cool weather approaches because it gives you the opportunity to reduce mite counts to protect the developing winter bees. Getting your mites low in summer won’t win you any awards if you let the mite levels climb sky-high in the fall. Explore these tips for keeping up with your mite counts to prevent devastating infestation — and suggestions for additional mite treatment options if your first fails.
How do mite infestations happen?
Where do the mites come from, anyway? Well, initially, no matter how you got your bees — whether you hived a swarm, did a cut out, or bought your bees from a reputable supplier like Betterbee — the mites came with them. Because, as hard as we try (and we, and our bee suppliers, put in considerable effort), virtually no honey bee colonies can be guaranteed to be mite-free these days.
Even if a hive starts with the lowest possible mite levels, new mites can arrive with any returning forager through drift and robbing, particularly in closely spaced, managed bee yards. Perhaps even through a transfer at foraging sites, like individual flowers. Consider this short video of a mite on a daisy petal swiftly attaching itself to a visiting honey bee:
Video by Peck DT, Smith ML, Seeley TD from Varroa destructor Mites Can Nimbly Climb onto Foraging Honey Bees. PLoS ONE 11(12): e0167798. https://doi.org/10.1371/journal.pone.0167798
This startling video came out of a scientific study (led by our own Director of Research and Education, Dr. Peck) on whether mites could potentially transfer to foraging bees at feeding sites. The answer is, obviously, yes — although the study authors pointed out that no conclusions could be drawn about how frequently this may happen in the real world. Still, it provides evidence that mites can hop aboard a new host and move from one place to another pretty easily. And, we already know that bees can bring mites back from a robbing excursion. Read the full, open-access paper for more details.
Best methods for counting mites
New to counting mites? Don’t worry, it's never too late to start! We have instructions and tips to get you up to speed. Learn why it's important to count mites, discover how to use a mite monitoring board (even during the winter), and get instructions for how to do sugar rolls or perform an alcohol wash.
What is an acceptable mite count?
Mite treatment thresholds can be a little tricky since your mite level in spring will keep growing, while the same mite level in the fall probably won’t get much higher. Also, because people keep bees in very different regions, it’s hard to say that “mite levels in May should be below 9 mites per 300 bees,” because our colonies can be in very different situations during the month of May. However, we have grown to like the recommendations put out by the Honey Bee Health Coalition. The guidelines give the thresholds for mite levels when your colony’s population is “dormant” (like in winter), when it’s “increasing” (like in springtime), when the population is at its “peak” (like summertime), and when it’s “decreasing” (like what happens in autumn around here).
Treatment Thresholds Based on Recommendations from Honey Bee Health Coalition:
| Colony Phase |
Action Not Needed Yet |
Treatment Needed |
| Dormant |
<1% |
>1% |
| Increasing Population |
<2% |
>2-3% |
| Peak Population |
<2% |
>3% |
| Population Decreasing |
<2% |
>2-3% |
% = #mites/100 bees found using an alcohol wash or sugar shake sample
How to treat infestations after mite counts
The best way to prevent mite infestations is to keep up your mite assessments as long as it’s still warm enough to do them. Then, if you find a spike in the numbers, another round of treatment can push the levels back down.
With your supers off, products like essential oil based ApiLife Var or Apiguard, or amitraz-based Apivar are useful to knock mite levels down so that the remaining brood can develop in peace.
With the natural reduction in brood rearing, as we get closer to winter, oxalic acid vaporization treatment is a seasonally appropriate choice. OAV has a very low risk of queen injury — an important factor late in the season when replacing a lost queen would be hard. Vaporizations need no opening of the hive and the series of treatments can be flexible to meet repeated upticks in mite numbers while bees are still flying out of the apiary.
For spring or summer treatment, a good option is Formic Pro, a formic acid treatment that can be used with honey supers in place. The benefit of this treatment is that it kills varroa mites in all areas of the hive, including under brood cappings. Treatment should be done when the air temperature is above 50 degrees, but no higher than 85 degrees — higher air temperatures can result in significant population loss or contribute to queen issues during or after treatment.
The battle against varroa mites takes a watchful eye and persistence, but you can succeed if you keep up with your mite counts and recommended pest treatment methods. For more pest management tips and techniques, explore our Beekeeping Guide for beginners and experienced beekeepers alike.
