I’m not sure if varroa mites are the thing I write about most, or if it’s queens, but they both feature heavily, and with good reason. If I have good queens in my colonies and varroa is under control, then the chances are that my bees will do well. Anyway, it was pointed out to me recently that I said that beekeepers should try to keep the number of mites in a colony below a maximum number of 2,000, and that this is out of date. I’ll get to that later on, but for now, I thought this would be a good opportunity to provide my latest advice on varroa, which supersedes previous articles.
Podcast
I now have a proper podcast channel which you can listen to through many standard podcast apps (Apple Podcasts, Spotify, YouTube). Sometimes my AI assistant Imogen just reads my blog, and sometimes I waffle on adding a bit more context to what I have written here. I know that many people prefer to listen rather than read, so give it a try. It’s called The Walrus and the Honey Bee.
Two Broad Directions
There are two broad directions you can go with this subject, and I will cover both. One way is what I suppose you could call “traditional.” The other is working towards being “treatment-free.” From what I have seen, there is a great deal of interest among hobby beekeepers in the latter, whereas most commercial beekeepers tend to be more in the traditional direction, which also reflects current advice from the National Bee Unit (NBU). I know that not everything is always completely up to date on BeeBase, but luckily the advice on varroa was recently re-done.
I’m a Treater
I have gradually evolved into somebody who believes that applying three different varroa treatments per season is correct for me and my bees. I used to think that two treatments would work, and it mostly did, but there were casualties. I used to apply thymol at the end of summer, after the last supers were off, and I would follow that up with oxalic acid in the winter. Thymol treatment requires two brood cycles (6 weeks) and does hinder the laying of many queens, so I now favour formic acid for larger colonies (it’s much quicker) but continue to use thymol on nucs.
Alcohol Wash
A few seasons ago, after visiting Randy Oliver at his place in Grass Valley, California, I decided to try to perform an alcohol wash on every one of my production colonies. I think at that time it would only have been about 20 colonies, but that seemed like a lot of alcohol washes. When I did those washes, in June, I found something similar to what Randy found in his colonies. Many had low numbers of mites, but a few colonies had far too many. Anything under 6 mites from a sample of 300 bees was below my treatment threshold, and most colonies comfortably sat in that group.
Outliers
There were colonies, however, that showed 12 or 16 mites per 300 bees, which meant that they were highly infested. Something had to be done to stop them from dwindling away and dying. Back in the day, MAQS was the answer, but in the UK the equivalent product (Formic Pro) should not be used with supers on. Well, supers were on in June. I actually did treat with formic acid that time, as I was ignorant of the rule-change, but now I can’t use it as I have caught up.
The only things I could think of to explain high mite levels in some colonies were:
- I forgot to apply oxalic acid on them the previous winter
- When I applied oxalic acid, they were not broodless
- Some kind of drifting/robbing phenomenon (maybe due to being at the end of a row of hives)
As it turned out, in one season I did miss out an apiary from oxalic treatment in the winter, and those colonies did, in fact, have higher mite counts in their alcohol washes. The winter oxalic treatment really is worth it. That was a one-off, so where the occasional highly infested colony sprang up in June, my suspicion is that they had some brood – maybe even half a frame or so – at the time they got their winter treatment. I think the drifting/robbing scenario would be more likely to apply later in the season.
Dealing with mites in Summer
So, what are you supposed to do with a strong colony in June with 2 – 3 supers on, when it has too many varroa mites? There are no authorised treatments in the UK for when supers are on. What I would do is wait until any nectar flow is over (it usually goes quiet sometime in June), whip off the supers, add back some empty supers for space, and treat with Formic Pro. Another, more drastic option, might be to do a shook swarm on that colony and treat with oxalic before any of the new brood is sealed. That would certainly give them clean frames and reduce virus levels, but it’s probably the end of any chance of a good summer honey crop from that one.
The Solution
My preferred approach to this conundrum is to go crazy and introduce an additional treatment in early spring, using amitraz. I now put strips in the colonies on 1st March and remove them in April, which means that there are never any mites in June, or so few that it’s not worth worrying about. This then renders the June alcohol wash pointless. They get three treatments per season, and mites are fully locked down. On the downside, I can no longer spot colonies that might display signs of varroa resistance. And that is sad because I would like to try to raise future generations from queens that are good at both honey production and mite resistance.
Treatment Free
For those optimists who want to try to redesign the genetic landscape of honey bees in our country, a handful of colonies at a time, there is the treatment-free pathway to nirvana. The science is there; it is possible to breed varroa resistant bees, but it’s not necessarily something I would recommend for a new beekeeper. There are different ways to go about it, and I’m strongly against the so-called “James Bond” method (live and let die).
It seems to me that the people who have any success with following this path live in an area where they are pretty well the only beekeeper for miles around. Or they are in some remote location, or on an island. I suppose the UK is an island, but I mean something smaller. With a stable population, and no movements of bees into or out of the area, it is more likely that a breeding program will work. The reality is, in England at least, such places are extremely rare.
Anyway, my objections to letting nature take its course, losing 90% or more of your bees after a couple of years of not treating, then breeding from survivors are:
- you create a genetic bottleneck (lack of diversity going forward)
- you could lose many of the desirable traits such as gentleness and high honey production in favour of one trait (varroa resistance)
- It’s not good animal husbandry to let your livestock die from a vicious parasite that was, after all, introduced to honey bees by beekeepers.
Randy Shows The Way
The method followed by Randy Oliver is the only one that really makes sense to me, and his way works because, in his area, he’s by far away the biggest beekeeper. His bees dominate the land. He does not just prioritise survival. He wants great bees, that any commercial beekeeper would be happy to own. The breeder queens have to show that they (a) keep mite levels low throughout the season with no treatment and (b) are good bees, with low swarming, low defensiveness, and good honey production.
Importantly, he carries out regular alcohol washes on all colonies (a massive undertaking), and can quickly spot the colonies that can’t cope with the mites. The queens who head those non-resistant colonies are then out of the breeding program. But the colony is not left to die; it gets treated and continues to thrive. Initially, from over 1,000 colonies, he only found 50 that displayed the desired characteristics, and these became the breeders for the next generation. Then the non-resistant colonies were split and re-queened with daughters of the resistant queens, and so on. Repeating this year after year has led to some progress, but he is not claiming complete success.
Quotes from Randy Oliver:
Note to hobby beekeepers: I say this to make clear that beekeeper Jane or Joe Treatment-Free is dreaming if she or he think that allowing their colonies to die from lack of mite management is going to improve honey bee genetics overall. If they want to improve honey bee genetics, they’d do best to treat their hives to keep them healthy, but put pressure on whoever they purchase queens from to seriously select for mite resistance.
I gotta tell you though, seeing these strong, gentle, productive hives that are able to maintain minimal mite levels over the course of an entire year of near-continuous brood rearing in California has got my crew danged excited about the possibility of a future in which we would no longer need to worry about varroa and its associated viruses.
Worth Chasing
The thing is, even if you manage to produce great bees that only need one treatment per year, that is still a big win. They may not be treatment-free, but they are a stepping stone. Fewer chemicals in the hive, less expense for the beekeeper – it’s a prize worth chasing. Not for me, though. My part of the country is not isolated, there are plenty of bees moving about, and my bees don’t dominate the land. I don’t have 1,000+ colonies. Randy is still making progress after more than five years, but he’s not at the promised land yet, and it would be too much for me. I know my limits, and what’s likely to work. I would be happy to use breeder queens from a large-scale queen breeder who has achieved resistant bees that are also gentle and productive, and I do favour hygienic bees currently.
Mite Monitoring
If you zap the hell out of mites three times per year, there is not so much need to monitor them. If I was going to do it, I suppose it would be to check them after the summer harvest, out of curiosity. They would probably all be getting treated anyway, but who knows, it might tell me something.
The latest advice, from both Randy Oliver and the NBU, is to keep mites down throughout the season rather than letting them build up high and having to knock them back. Ideally, the maximum number of mites should be below 2% infestation and less than 1,000 in total, to keep down associated viruses. The NBU Best Practice Guideline 11 also says that at 2,500 mites in the colony it will suffer serious damage due to virus build up. However, their Managing Varroa Leaflet, which, I think, is very comprehensive and worth downloading and reading, re-states the 1,000 maximum limit.
If you are going the treatment-free route, then mite monitoring should be something you do almost continually so that you can understand what is going on in your colonies. Unless you just want to let most of them die, which is not what I think keepers of bees should be doing.
The question then becomes, how should I monitor mites? Well, there’s various advice out there. In the UK many people use open-mesh floors, which I don’t really like, but if you do, you can monitor natural mite drop onto a sticky board below the mesh. Most people don’t use a sticky board, which does not help. I don’t trust the natural mite drop, and can’t monitor it anyway, due to solid floors. In fact, the only thing I half-trust is the alcohol wash; it’s not perfect, but I think it’s the best way to get an approximation of infestation. Whatever you use, if you are not treating, I think you should be using it often and on all colonies.
Surviving or Thriving?
That way, you can have actual data to back up your potentially wishful thinking that you have just created the perfect varroa-resistant bee from your three hive apiary in your garden. Is ‘survival’ good enough for beekeepers? Don’t you want vigorous, healthy colonies that are a joy to work, and make loads of honey? So keep records. Maybe try having some treatment free colonies, and some run along traditional lines. How do they compare? Are you really sure this treatment free idea is all it’s cracked up to be?
The Managing Varroa Leaflet from the NBU has a list of scientific studies in the ‘References and Further Reading’ section at the back. Some of these are very interesting, and my eye was particularly taking by the following, which rounds up the state of play in the science of varroa-resistance in honey bees:
Mondet, F., Beaurepaire, A. McAfee, A., Locke, B., Alaux, C., Blanchard, S. and LeConte, Y. (2020) Honey bee survival mechanisms against the parasite Varroa destructor: a systematic review of phenotypic and genomic research efforts. International Journal for Parasitology, 50.
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