Coordinated Varroa control

Synopsis : Our recent study on landscape-scale coordinated Varroa control suggest there are benefits for colony health. I know it makes sense, but how many actually do it?


In the magnum opus last week I discussed how bees discriminate nestmates from non-nestmates at the hive entrance. Inevitably I had to discuss the processes of drifting and robbing as these activities, together with the peripatetic drones, largely account for the ‘foreign’ bees arriving at a hive entrance.

I described drifting as a short-range phenomenon, predominantly of bees with immature cuticular hydrocarbon profiles 1, on their first few orientation flights. In contrast, I described robbing as a potentially long-range event that could occur over at least one kilometre.

I should have re-read the literature and refreshed my memory of what others have already reported for these activities before writing the post 🙁 .

Peck and Seeley (2019) demonstrated the importance of robbing in mite transmission, and – of necessity – discriminated between bees that were robbing and those that were drifting. In their study they demonstrated drifting occurred over distances of at least 300 metres, much greater than I remembered.

Not such short-range after all.

In addition, I re-discovered Eva Frey’s paper (Frey et al., 2011) on robbing, showing it occurs over at least 1.5 km.

Both robbing and drifting of workers, and possibly drifting of drones, mediate the transmission of Varroa and deformed wing virus (DWV) between colonies in the environment.

All of which means that when you’re considering Varroa control you should not restrict your thinking to your hive, or the hives in your apiary, but should instead consider a much larger area encompassing other colonies “within range”.

Colonies in the environment

I’ve discussed this general topic before, so I’ll try and whizz through it quickly.

The hive vs the apiary

Your hive sits in your apiary.

It may be the only hive in the apiary or it may share the space. The other hives in the apiary may be yours, or – in the case of an association apiary – may belong to others.

Gaffer tape apiary

The association apiary …

You should consider all the hives in the apiary as a single location. The bees will move between them reasonably freely and the Varroa and virus will be shared out … not necessarily equally, but they will certainly be well distributed between all the hives in the apiary.

I’ve previously moved mite-free colonies into infested apiaries. Mites are detectable in the introduced colony within days, and DWV symptomatic bees within a month or two.

When it comes to applying the late summer miticide treatment to colonies it makes zero sense to treat hives within the same apiary at different times. Equally, it makes no sense to treat some and not treat others.

Are you sure some really have a lower Varroa infestation level (the only possible justification I can think of to not treat them)? Have you conducted phoretic mite counts i.e. sugar roll, or alcohol washes?

Even if you’ve done these, are you sure there are similar capped brood levels and the queens have been laying at equivalent rates? These, at least theoretically, influence phoretic mite levels.

Different hives and different beekeepers taking honey supers off at different times? 2

Find a different apiary and move your bees there 😉 .

That may sound flippant, but I’m completely serious

Imagine the scenario. You have a couple of hives in the association apiary. There are the association hives and a handful belonging to another couple of beekeepers – let’s call them Laurel and Hardy.

You, the association apiary manager and Laurel take your honey supers off in mid-August. You live somewhere relatively warm and so use Apiguard to treat the colonies. Apiguard is applied for one month. Much later than mid/late September and it would be too cold for effective treatment anyway.

Hardy however has different ideas. He’s away most of August. By the time he returns he reckons he can get ‘a bit more honey’ from the rosebay willow herb. Before you know it his supers are still on and it’s late-September. By then the ivy is yielding and Hardy’s getting greedy … he delays treatment a bit longer.

Mites have been replicating in Hardy’s colonies for at least a month more after you applied miticide to most of the hives in the apiary. Mite levels will now be significantly higher. If the weather stays warm and the bees continue to rear brood – and go on orientation flights – the mites from Hardy’s colonies will end up in all the recently miticide-treated colonies in the apiary.

Thanks … for nothing!

Willow herb (fireweed), mid-August 2015

But it could be worse.

Hardy 3 failed to treat his colonies last year at all and they are absolutely hooching with mites.

Riddled, they are. Boggin.

And, shortly after he returned from his August holiday and hoped to squeeze another super of honey from the RBWH, his colonies started collapsing with varroosis.

And so your miticide-treated colonies start robbing out his expiring mite-infested hives.

You may as well have not treated … 🙁 .

The apiary vs the environment

So, you sensibly move your colonies from the shared apiary into one you have total control over.

You can treat when you want. You no longer need to consider Hardy and his attempts to become a world-champion mite keeper.

Your troubles are over … or are they?

Hardy’s mentor – who taught Hardy all he doesn’t know about mite control – keeps bees on the other side of that distant copse at the end of the field.

They’re no more than 300 metres from your apiary … but you didn’t even know they were there. Hardy’s mentor visits them so infrequently you’ve never seen him.

If you think this is an unlikely scenario, think again. Do you know of every hive-shaped nook or cranny within 300 metres of your apiary? What about 1.5 km?

What about all those urban beekeepers who may not even know their neighbours, let alone the contents of their high-fenced back gardens?

How many urban back gardens are there within 1.5 km? … hundreds, thousands?

City rooftop bees

Or urban rooftop bees …

Your bees almost certainly share the environment they occupy with lots of bees from other hives. Yes, there are certainly exceptions, but the vast majority of honey bees in the UK will be in this type of environment.

And that’s before we consider the feral colonies … which we won’t.

Hive density in the environment

If your apiary is registered on the National Bee Unit’s Beebase system (and it jolly well should be) you can get a pretty good idea of the local hive density.

Beebase shows the ‘density’ of apiaries within 10 km

The figure in the column ‘apiary density within 10 km’ can be used to calculate the approximate number of hives in the ‘local’ environment.

You have to make some assumptions here … there are ~ 50,000 beekeepers running ~250,000 colonies in the UK. Some are commercials, many of which move their bees around the country (so could ‘occupy’ several apiaries in a single year).

Some apiaries will have just one or two hives, others might have 20 or more.

My guesstimate is that the average UK apiary contains 5 hives.

Go on … show me I’m wrong 😉 .

I’d love to have some accurate data here but it’s all wrapped up with the NBU and Data Protection Act.

I’ve quoted 5 before and no-one has suggested I’m a long way out.

A 10 km radius produces a circle with an area of 314 km2 . The Beebase figure tells us the number of apiaries within that area. You can therefore calculate the number of hives per square kilometre within that circle, and from that, the number of hives within 1.5 km or 5 km.

But I’ve saved you the effort … 4 

Hive density – see text for details

Why 1.5 and 5 km? The first is the distance over which Frey et al., (2011) showed robbing occurs, and the second (5 km = ~3 miles) is often quoted as the maximum foraging range of a worker 5.

So, if Beebase informs you there are 100 apiaries within 10 km you could reasonably expect there might be 11 hives within robbing distance of your hive, or 125 hives within worker flying range.

How accurate are these figures?

I don’t know.

When I lived in Warwickshire there were about 250-275 apiaries within 10 km of mine. Almost every field seemed to have bees on it. My short evening walks would take me past a couple of dozen hives belonging to other beekeepers.

A very careful look at Google maps satellite images turned up two apiaries within ~3 km I never knew existed (and I’d been living there for several years).

When I talk to associations about bait hives I ask them the postcode of their association apiary and look it up on Beebase. Many have 150 or more apiaries within 10 km. Some have almost 300. It’s very high in some cities.

My Fife apiaries have 50-60 within 10 km. One is on the edge of a town and I’ve no idea where other bees are. I know of at least a dozen other hives within 1.5 km of my rural apiary.

Apiary density (those I knew of … there were more) in Warwickshire. Scale bar = 10 km. Circles are 1.5 km radius.

Check your apiaries on Beebase.

Check my maths 😉 .

You might be surprised.

This is the environment in which you are trying to control Varroa infestation.

And all of the above assumes that hives are static. They’re not. Beekeepers are forever moving them about … between apiaries, selling them, moving them to the OSR or whatever. All of this just makes the problem worse.

Of course, hives are not evenly distributed in these neat circles of radius 1.5, 5 or 10 km, but let’s not make it more complicated than it already is 😉 .

Read the instructions

In Infernal contradictions I discussed the poor quality instructions that accompany some miticides sold in the UK. Only some because I ran out of space. I have yet to write about other miticides which are also supplied with equally shonky instructions.

Bad, but in different ways 🙁 .

However, one thing that most 6 miticide instructions state is something like:

Treat all colonies in the apiary at the same time (MAQS)

Treat all colonies in an apiary simultaneously (Apivar)

All colonies in the same apiary should be treated simultaneously to avoid reinfestations (Api-Bioxal)

Kudos to Api-Bioxal for explaining why; instructions make more sense when there is some explanation included.

The miticide manufacturers generally appreciate the importance of coordinately treating colonies in the same apiary. That’s a good start.

But – based upon the scenario with Hardy’s mentor outlined above – why is there never any mention of collaborating with neighbouring beekeepers to coordinately treat all the colonies sharing the environment?

That’s a rhetorical question.

I can think of several likely answers; some of these reflect badly on the manufacturer, some reflect poorly on the beekeeper, and most of which are because it’s not necessarily a very easy thing to achieve.

Which doesn’t mean you shouldn’t try.

Landscape-scale coordinated Varroa control

There is compelling science that shows the ‘environment’ used by your colonies extends well beyond the confines of the apiary, and that it is probably shared by many other colonies 7.

However, there are numerous examples of successful coordinated pathogen and/or parasite control at the landscape-scale; sea-lice in salmon farms, cattle tick fever, visceral leishmaniasis, mosquito/malaria/Zika virus etc.

I’m aware of at least two previous attempts at coordinated Varroa control. They were either small-scale and/or inconclusive. This isn’t a criticism … these are not easy experiments to do.

As we discovered 😉 .

Full disclosure: I’m the senior 8 author of the study I introduce below on coordinated Varroa control at the landscape scale.

The density of managed colonies in the UK makes any sort of comprehensive landscape-scale control initiative very difficult to study. Not all colonies are documented, not all beekeepers are known, not all want to take part etc.

What we needed was an isolated area with a reasonable number of colonies that could be managed coordinately. The obvious choice was an island, separated from other bees by an expanse of water over which bees were unlikely to fly.

After discussions with our collaborators in SASA 9 and SRUC 10 we approached the Arran Bee Group (ABG) on the Isle of Arran. All the known beekeepers on the island belong to the ABG.

Arran, the ABG and the study design

Arran is a 430 km2 island in the Firth of Clyde. There are ~4700 residents of which ~50 are beekeepers who were managing 57 colonies at the outset of the study. Arran is a popular tourist destination with, amongst other attractions, excellent hillwalking in the central upland areas. Most residents live around the coast, in small towns or villages such as Brodick, Lamlash or Lochranza.

Cir Mhor and Caisteal Abhail from Goatfell, Arran

The ABG very generously agreed to take part in the study. Essentially this involved coordinated late summer miticide treatments using Apivar, followed in the winter by an application of trickled Api-Bioxal. The latter was not coordinated as there is no drifting or robbing (or flying for that matter) happening in December.

Each summer for three years Luke Woodford, my then PhD student (and now a post-doctoral fellow in the University of Stirling), would visit the island to apply the coordinated treatment, more than ably helped by Graeme Sharp from SRUC.

I would sometimes tag along to get in the way, chat with beekeepers and cause problems.

At the same time the summer miticides were applied Luke would take a sample of nurse bees to test for viruses. The ABG would collect all the mites that dropped during treatment and post them back for analysis in St Andrews.

Lamlash dawn looking to Holy Island

An important component of the study was that the importation of bees was stopped during the study. This would have otherwise been a source of new viruses and Varroa which would have confounded the (already extensive) data analysis. The ABG also documented the movement of hives and nucs between apiaries on the island.

It’s worth emphasising here that this study would not have been possible without the enthusiastic support of the ABG for which all the authors are extremely grateful.

Results in brief

The paper is freely available (Woodford et al., 2023) … it’s not necessarily ’easy listening reading’ but the bits that I didn’t write are relatively straightforward to read 11. The study started in mid-2017 and ended in late summer 2019.

The Isle of Arran

The key results were as follows:

  • 29/57 colonies were lost in the first winter due to a combination of adverse weather and high mite and virus levels. We presume that our initial treatment was applied too late to save colonies with pre-existing high mite levels.
  • By the end of 2018 ABG managed 54 colonies, and this number increased to 84 colonies by the end of the study period in 2019.
  • Average mite drop/colony in the 7 days following summer Apivar treatment was 683 (2017), 226 (2018) and 303 (2019). Overall there was a reduction in mite levels across the island of ~60%.
  • Average DWV levels dropped from 8 x 105 in 2017 to 4 x 104 in 2019 12. This is a 20-fold reduction in virus levels.
  • We observed a shift (partial or complete) of a type A strain of DWV to a type B strain across the entire island, possibly due to the origin of nucs and/or the replication characteristics of the virus.
  • There was considerable apiary-to-apiary variation in terms of mite/virus level reductions, probably due to different management methods, forage, colony genetics or one of a thousand other potential variables.
  • There were no controls.

What? No controls? No funding?

Generally scientific experiments are ‘controlled’ by conducting a parallel set of studies in which only one thing is varied.

For example, the coordination or not of the miticide treatment.

By doing this you can determine whether the thing you are testing has a significant impact on whatever you are investigating.

But that’s a problem in this type of study. It would mean we would need to find another 430 km2 island off the west coast of Scotland, sharing the same climate, forage, number (and experience) of beekeepers, colony numbers, management methods etc.

Nope … not going to happen.

There are other ways to control for variables such as weather but these almost always involve multiple repeats over many years.

All of these things make the study less definitive than it could have been. Money and time were also finite.

As an aside, we had approached one of the beekeeping charities to fund a small part of the study. They politely refused stating that ’whilst the science is excellent you will not get the beekeepers to work together and collaborate with you’.

Thanks … for nothing!

Frankly, that was the easy part. ABG could not have been more welcoming and accommodating.

Take home messages

Despite the absence of controls I think there are some very positive outcomes from this study.

Mite and virus levels decreased significantly during the study period over the island. Equally importantly, and I would argue as a consequence of the resulting improvement in colony health, the ABG readily made up colony losses experienced in the 2017 winter, and ended up with significantly more colonies than they had started with.

It should be noted that we only provided advice or practical instruction in Varroa management and that the ABG had previously suffered unsustainable colony losses attributed to mites and the viruses they transmit. However, with healthier colonies they were better able to make increase’.

Isolated apiaries on the island tended to have lower mite levels by 2019 and showed the greatest decrease in mite and virus levels.

In contrast, one site (containing three neighbouring apiaries) had resolutely high virus and mite levels throughout the study. Colonies moved from here to remote apiaries 13 were associated with exacerbation of mite and virus levels at the landscape level.

It seemed likely to us that the management of these colonies, or the local environment, was conducive to either better mite reproduction (e.g. more drone brood in the colonies) or less effective miticide treatment outcomes.

The island-wide replacement of one type of DWV with another was interesting, and has also been seen in other survey-type studies. There are suggestions that type B DWV persists in miticide-treated colonies, whereas the type A variant is dependent upon mites for sustained transmission and is lost (or at least significantly reduced) when mite levels are lowered. We have previously demonstrated that type B DWV replicates in mites, in contrast to type A DWV (Gusachenko et al., 2020).

More work

Clearly more work is needed, but I think this is a promising start 14.

However, even without good – well controlled – scientific evidence showing dramatic improvements in colony health attributed to reductions in mite and virus levels, our understanding of the biology of honey bees strongly suggests that coordinated miticide applications during late summer will be beneficial.

How that is best achieved on a scale larger than that of individual apiaries remains to be determined. At the very least, associations should promote it amongst their members, and government bodies involved in bee health should encourage it.

Varroa control is simple in principle, but difficult in practice.

The timing of both the summer and winter treatments is critical. The former must be early enough to protect what should be the long-lived winter bees. The winter treatment must be during a broodless period for maximal efficacy.

This timing may differ from year to year, and definitely does differ across the country.

And if that wasn’t difficult enough to grasp I’m now advocating coordinating one of these critical events – the late summer treatment – with all your neighbouring beekeepers.

Go for it!


Frey, E., Schnell, H., and Rosenkranz, P. (2011) Invasion of Varroa destructor mites into mite-free honey bee colonies under the controlled conditions of a military training area. Journal of Apicultural Research 50: 138–144

Gusachenko, O.N., Woodford, L., Balbirnie-Cumming, K., Campbell, E.M., Christie, C.R., Bowman, A.S., and Evans, D.J. (2020) Green Bees: Reverse Genetic Analysis of Deformed Wing Virus Transmission, Replication, and Tropism. Viruses 12: 532

Peck, D.T., and Seeley, T.D. (2019) Mite bombs or robber lures? The roles of drifting and robbing in Varroa destructor transmission from collapsing honey bee colonies to their neighbors. PLOS ONE 14: e0218392

Woodford, L., Sharpe, G., Highet, F., and Evans, D.J. All together now: Geographically coordinated miticide treatment benefits honey bee health. Journal of Applied Ecology n/a


  1. My speculation, but I’m repeating it here to claim priority over the idea ;-)
  2. i.e. some cannot be treated as the miticide is incompatible with the presence of honey supers, as almost all of them are.
  3. Who you’re beginning to realise is a bit of a clown.
  4. You can thank me later.
  5. Except it isn’t the maximum range, but it’s rare they travel further.
  6. Not all … Oxuvar appears not to mention this. Tut tut.
  7. And possibly some feral colonies.
  8. Age, if nothing else.
  9. Science and Advice for Scottish Agriculture
  10. Scotland’s Rural College
  11. And better punctuated than these posts.
  12. Units are a confusing Genome Equivalents per microgram of total RNA per worker (I bet you’re sorry you asked).
  13. We did not restrict how the ABG managed their bees.
  14. But then I would, wouldn’t I!

42 thoughts on “Coordinated Varroa control

  1. Thomas

    Excellent post. One question: do you know of any studies that have looked at the impact of installing robber screens? If robber screens could reduce the number of drifting bees in certain hives within an apiary, maybe we would see a reduction in mite and virus levels within the protected hives?

    If the study has not been done, then you should please do it. Plus, it would be a lot easier to have a control group! 🙂

    1. David Post author

      Hello Thomas

      Do robbing screens reduce drifting? I don’t know and the processes are a bit different. Robbing screens to reduce robbing might prevent the transmission of mites from collapsing colonies to strong, healthy ones … but, you’d be dependent upon beekeepers who had let their colonies succumb to varroosis fitting the robbing screens. I suspect that’s not something you should rely upon. Maybe you could persuade ‘Hardy’ in the post above to fit robbing screens, but my bet is a) he wouldn’t know what a robbing screen was, b) he wouldn’t have a robbing screen to fit, and c) if provided with them. he’d forget!

      Not actually an easy experiment to control … you’d need to create a weak colony, susceptible to being robbed, and then co-locate it with one or more strang colonies so it was robbed. The nectar flow would influence things. You’d then need to monitor mites acquired by the strong colonies plus/minus the robbing screen, perhaps on alternate days.

      Having thought about it I think I’ll leave it for someone else to do … 😉


      1. Thomas

        I guess I assumed that robbing screens would reduce drifting, but I can’t prove that. Maybe that’s the first study that could be done.

        I really think that your statistic that 40% of bees in a hive drifted is absolutely earthshaking, and explains much of why bees are failing to thrive. When bees are normally live in the wild in widely scattered hollow trees, drifting must surely be a rare event. It makes sense then, that bees would have very little genetic resistance to help them ward off the constant barrage of novel pathogens brought in by drifting bees.

        Keep up the good work.

        1. David Post author

          Hi Thomas

          Don’t get me wrong, robbing screens may stop/reduce drifting, but it would need to be proven.

          The Peck and Seeley study I quoted shows that robbing, not drifting, is the major route by which Varroa are introduced. And robbing is likely to occur over the distances that ‘natural’ colonies are spaced. However, Seeley also shows that it is detrimental to have hives closely spaced. If we choose to do the latter – which for pragmatic reasons we do – then it’s important to either accept the consequences (losses), or manage the mites rationally.


  2. Tracey Mackenzie

    Great reading. Thank you. It raises an important challenge for me. I live on Exmoor, my 3 hives enjoy the heather during August going into Sept. Once the supers are off I treat with apiquard mid Sept & have been lucky with good warm weather. I also use O Acid, dribble method in late Dec.
    I use varroa boards coated with vasaline and never see a heavy drop. Any thoughts would be greatly received.
    Kind regards, Tracey.

    1. David Post author

      Hi Tracey

      Lovely part of the world … if your bees are overwintering successfully with no losses then you probably have a system that works. I suspect they’re never broodless in winter, so you might choose to time the winter OA for the time when there’s minimal brood. Finally, a cold autumn might restrict winter bee production, leaving those produced before mid-September exposed to higher than desirable levels of Varroa.

      But the key thing is whether the colonies survive overwinter and are strong in the spring. If they are, then don’t change a winning formula 😉


      1. Tracey Mackenzie

        Many thanks for your thoughts & coming back to me. I’m trying hard to find the right process for managing varroa here on Exmoor. I’m now going on beebase to check out how many apiaries around us. Bees 👍 always a challenge.

        1. David Post author

          If they weren’t a challenge managing them would be a whole lot less rewarding … it would be more like growing potatoes.
          Less rewarding and a lot less fun 😉

  3. Paul Dosen

    Hi David,

    Haven’t read the post yet but given how good your previous posts have been, I’m looking forward to this one with great anticipation for sure. David, I was wondering if you could please send me a some “leave and let die” studies that have been conducted throughout England, as some of the treatment free advocates that I’m in contact with claim all of the studies done measured mite counts and not survival and I would like to see for myself weather or not this statement is in fact correct or not. Figured you’d be the perfect person to ask and was hoping you could point me to some compelling studies. I was able to dig up 3 studies conducted in North America but figured I’d look overseas as well.

    Thanks so much David,



    1. David Post author

      Hi Paul

      I could be wrong but I’m not aware of any published, peer-reviewed ‘leave and let die’ type studies in England. If there have been any, I’d like to read them as well. Ron Hoskins’ bees (Swindon) were used in studies by Declan Schroeder a few years ago but I seem to remember they had high mite counts and survival was not measured in the studies they conducted.

      Not England, but the Gotland study is one of the classics … Fries, I., Imdorf, A., & Rosenkranz, P. (2006). Survival of mite infested (Varroa destructor) honey bee (Apis mellifera) colonies in a Nordic climate. Apidologie, 37, 564–570. They started with 150 colonies and 5 years later had 11 survivors if I remember.

      Of course, if you want to see the true devastation that Varroa can wreak there’s the deliberate use of it on Santa Cruz Island to eradicate honey bees.


  4. James

    So if I have 200 apiaries within 10km of mine and I make sure I have 23 colonies in mine then like Baldrick keeping a bullet with his name on it, I’m sorted, right? 🙂

    More seriously, how confident do we feel that there will be no drifting during the winter, particularly in the south of England where thanks to the way our weather is changing we’re probably not far off having bees out collecting water and/or pollen on any sunny day when it’s over 5°C (of which there have been quite a few this winter). If there’s the potential for drifting, given that we know colonies will not all be broodless (or have minimal brood levels) at the same time and that periods when the bees may not be flying may not coincide with zero/minimal brood levels, is there an optimal treatment strategy and if so is it one that is actually currently legal?

    Fascinating article. Thank you.


    1. David Post author

      Hi James

      On the first point, quite probably not I’m afraid … hives aren’t evenly distributed. There could be another 1977 hives on the other side of your apiary fence 😉

      I’d assume that winter orientation flights would be directly related to brood rearing and this is very much reduced. Therefore the likelihood of drifting is also much reduced. I comment elsewhere on the effect of temperature on orientation flights – does it shorten them? In which case, drifting will be less still.

      There isn’t an optimal treatment strategy that takes into account all the variables you mention – although arguably Apiguard in late summmer (when it’s warm) and Apivar midwinter (which is temperature independent) might be an option. I don’t know anyone who’s actually done this … 😉


    2. Dino

      We have opportunity to test this theory in practice. Check web page dedicated to coordinated varroa control
      There is included also mathematical model to calculate colony varroa invasion potential, based on geographical beehive density.
      I’m looking forward to find group of beekeepers located relatively close to each other so they can test treatment coordination in practice.

      1. David Post author

        Hello Dino

        We worked with ~50 beekeepers running ~100 colonies – the paper is listed somewhere in the post. It was a lot of work. The key thing is to have an area with clearly defined boundaries or your studies will constantly be plagued with the import of mites from outside the study area. We chose an island, but there are other ways to do it. The beekeepers also ‘banned’ imports of bees to the island for three years.

        It is worth spending a lot of time talking with your beekeepers. We gave talks each year, did a lot of the mite control and sampling, prepared all the winter treatments etc. Some of the beekeepers will be experts, some beginners. You cannot assume they are all equally experienced (well, you can, but it will cause problems). We were very fortunate to work with such a great bunch of people on Arran.

        Good luck

  5. Steve Donohoe

    Boggin! Love it.

    It all makes perfect sense to me. I will try to spread the coordination word in my association.

    Some beekeepers listen to talks by biology professors who have found evidence of some bees that can survive without treatment, and they think, “that sounds like a great idea, I won’t treat my bees and they will naturally evolve immunity over the next few weeks.” Then, when their bees die (due to pesticides of course, or wasps – definitely not mites) they either give up or buy another nuc. Madness.

    1. David Post author

      Hi Steve

      Boggin. Just one of the vast range of wonderful Scottish slang words 🙂

      I can’t imagine who you’re referring to 😉 The Cuba story is really interesting. A ~50% loss of colonies and recovery over 20 years … could we face doing the same thing here? We’d have to make some dramatic changes, starting with a ban on all imports. I’m not sure commercial beekeeping would survive and I think a lot of amateurs would give up without a readily available supply of replacement queens.

      On the other hand … think of the premium you could sell your honey for 😉

      There’s going to be a follow-up post on coordinate treatment sometime in the future to cover a bunch of things I had to omit due to running out of space and time.


  6. John Hague

    Hi David,

    Thank you for a thought provoking post. Rational Varroa Control is logical, and I’m a convert. Co-ordinated Varroa Control as a next step makes sense, and worth beginning discussions with local beekeepers. you have, however, highlighted a significant ‘elephant just outside the apiary’ – the feral colony. There is no beekeeper to co-ordinate treatment with, and ethical, legal, and moral issues abound if one considers any action, such that any action beyond scrupulous management of ones own apiary seems impractical.

    Kohl et al suggest that, in German forests, ‘feral colonies’ represent, in most cases, re-colonisation of sites with swarms every swarm season, with just over 10% surviving a year . So if this can be extrapolated to feral colonies in the UK, then maybe a feral colony just outside the apiary may not be a huge problem; but it is bound to have an impact, and the potential harm that an unmanaged ‘varroa bomb’ close by ones apiary could cause is considerable, especially if one thinks that a contributing factor to the high annual mortality is a high varroa load.

    Supers off, Apivar on all over the district, 10 weeks later Apivar off, just in time for a spot of robbing and drifting as the feral colony enters a decline. (At least 10 weeks of Apivar protects the colony during the application period, compared to other shorter treatments)
    The broodless period OA treatment in Decemberish could rescue things, unless the feral colony is still hanging on, and there is a spell of warm or sunny weather.

    I know that you haven’t considered feral colonies, but I would be really interested in your thoughts. Most of us will have an unknown feral colony within drifting range, many of us will know of a feral colony close by…..

    Thanks again for another thought provoking Friday post.


    1. David Post author

      Hello John

      I have considered ferals, but I’ve not had the time or space to write about them in this context. I will. I discussed the German woodpecker-hole-nesting bees a few weeks ago. The data on feral overwintering success rates I’ve seen for the UK is patchy, but I’ve been exchanging emails with someone who will be checking feral colonies they know about shortly and hope to then be a little better informed.

      However, there’s a simpler way to think about things. If you are in a “250 apiaries within 10 km area” (and that’s not unusual) the prediction is that there are ~30 hives within 1.5 km and ~300 within 5 km … it seems probable that these numbers will be significantly greater than the likely number of feral colonies within the same range. Not certain of course, but based upon the feral colony numbers I’ve observed I think that’s a reasonable assumption to make.

      If I’m correct then I don’t think we need a solution for the feral colonies before we consider how best to treat our managed colonies. “Don’t let the perfect be the enemy of the good”. I’d suggest we do what we can for the colonies we do control, without worrying too much (yet) about those we don’t.

      I’ll be returning to some other aspects of this topic in due course.


  7. Harriet Kinloch

    Made me think of head lice control at my children’s primary school. All the parents would be asked to treat their children on the same day, plus a follow-up treatment. This made perfect sense because – assuming everyone complied – it dramatically reduced the risk of reinfection. Frustratingly the policy was discontinued, with predictable results.

    1. David Post author

      Hello Harriet

      What a great example 🙂 . I’ll try and dig out some data on that (likely to be documented as it’s human health-related and so there will be funding available) and use it in the future.

      Thank you

  8. Alan Jones

    Hi David,
    I’m never sure how accurate the Bee Base counter is, I have a home apiary and two out apiaries, one ten miles from home the other seventeen away ,yet, Bee Base say there are 71 hives within a 10 mile radius of all three,Coincidence???
    I have offered to treat hives in my village for free but have been told “no need my bees don’t have Varroa!!
    Brian Cox says “theres no point arguing with idiots!”

    1. David Post author

      Hi Alan

      I suspect it’s a coincidence, but who knows? The numbers around my apiaries do change periodically and when I check some other areas there are sometimes reasonable differences even for apiaries that are relatively close together.

      Excellent news that your village is mite-free … a little miracle-like oasis in an otherwise mite-infested environment. But, look on the bright side, potentially more customers for your overwintered nucs 😉


  9. Vince Poulin

    David this post requires a few reads. One excellent study – applied research – works for me. It is the way we individual beekeepers learn. So much here and in your last post its hard to digest all of it. Must say my history which you have influenced greatly concurs with the results found. In coastal BC I believe our mites levels are exceptionally high due factors this study helps demonstrate and those you have talked about frequently. That in the study mite drops were counted in hundreds, here in my hives I have in the past counted them – in thousands. This year an enormous difference. Much like the success seen in the ABG work. Why? Experience and a hateful respect for the damaging effects of Varroa combined with a persistent effort to apply effective mite reduction strategies. I’ve made all the mistakes you so notably discuss. Some not entirely “mistakes” just missed opportunities – e.g. proper mite treatment timing. We all have busy lives so much so beekeeping for some of us is a pleasure we share with others: fitness, travelling, family – you name it. Integrated varroa management takes a lot of time and effort. But necessary. it is looking good for this year so much I think my successes will look similar to your ABG work if not better. Last season: Queen exclusion – mite trapping. 2. Drone comb removal (dedicated frames) and, 3. OA treatments timed well were the strategy. I will know just how successful in 3-4 weeks. But mite drops over winter were all low. Nothing like previous years and I do not believe due to a “low” mite year as two of my friends lost there hives to mites. You have well pointed out drifting and robbing as a means of mite entry into hives. My queen exclusion efforts show this. Within weeks mites returned to hives where that technique removed a very high % of mites. Those mites came from elsewhere and fast. However, too late to hammer our winter bee production as happened in nearly all my previous years. I have not seen a single DWV bee this past winter. In two out of the 7-years I have kept bees we have had very high hive losses such as up to 70%. That means both new and the best beekeepers have been subjected to the impact of mites despite some excellent beekeeping. This coming season the plan is to continue improving the application of the three techniques I mentioned. An Important element is building the much needed drawn drone comb needed for queen exclusion traps and as free-standing frames.

    1. David Post author

      Hi Vince

      It sounds like your efforts are paying off … good to know.

      It’s worth noting that the mite drops I referred to were averages. We saw one or two colonies where the mites were so thick on the trays that you could trace patterns in them with your fingertip (though these may have been during a different study, not the Arran one … it was a few years ago now). I seem to remember having a conversation with Luke where we were deciding at what point to stop counting the damned things and just weigh them instead 🙂

      Drawn drone comb … timed properly, a foundationless frame will get largely drawn as drone comb when the colony is wanting to rear lots of drones i.e. pre-swarm season. If you usually use foundation that might save you a C$ or two. If you make them with bamboo skewers they’re drawn in panels and you can simply cut out the ‘thirds’ you don’t want. I’m going to write something more about foundationless frames shortly.

      Still definitely winter here, with colder weather moving in for the next week or so. I fear a lot of that early frogspawn I commented on a week or two ago is likely to get frozen solid 🙁


      1. Vincent Poulin

        David – yes on your bamboo skewers frames – they do go heavy to drone comb. Foundation-less frames similarly. The problem with incomplete drone frames is cleaning them. I used green plastic drone foundation frames for my traps but found my bees did not like them. Some drew out nicely but otherwise either avoided or not completely drawn out. Far better were foundation-less frames. Or any drawn frame from a super. I was looking for frames totally built out in drone comb. If fully drawn it was easy to clean them of mites and larvae by power washing with a garden hose. After cleaning bees had them ready for reuse in a few days. I’ll give special attention to building more drone comb this spring
        Weather is turning. Considerable new snow in the mountains but 9 degrees C down here at sea level. Lots of bees flying yesterday with 3 out of 4 hives going gang buster’s. However, one hive not a single bee. It was a trapped colony so raised concern. I thought possibly a problem but today the complete opposite. Out they came in nice numbers. False alarm. That said, one out of three at my nursery has not been active. No bees despite two adjacent hives fully active. I could be looking at a loss.

        1. David Post author

          Hi Vince

          Did you ever try just freezing a frame of drone larvae and then letting the bees clean it all out afterwards? A lot more gentle than a power washer. I’m pretty certain 24 hours in the freezer will kill all the Varroa. We froze thousands at work (albeit for longer) and they were as ‘dead as a doornail’ afterwards as far a we could tell.

          We’ve had freezing temperatures and stunning sunny weather … so I’ve been hillwalking.


          It’s still going to be a few weeks until I open a hive.


  10. John Eaden

    Thank you for another well thought out and informative post.
    In an ideal world there would be a cheap and effective treatment for Varroa – a selective miticide with no collateral damage to bees or other species which would deal with the problem. Oh I wish – though the research led by Prof Joel Mackay at University of Sydney is having a go at developing such a treatment based on ecdysone.

    Meanwhile I consulted BeeBase and found that here in suburban Manchester I have 399 apiaries within 10km! And that doesn’t include unregistered beekeepers or feral colonies.
    By your formula that means I have about 2000 hives within the 10km circle and about 500 within 5km and 45 within 1.5 km.
    I cannot begin to think how we beekeepers could co-ordinate Varroa treatment in this context. It would mean trying to coordinate the actions of hundreds of beekeepers in at least three different neighbouring associations. I also know of at least three beekeepers who are members of none and who eschew Varroa treatments because they espouse “natural beekeeping “ – I.e. treatment free.

    My policy has been to look after our bees as best possible and following advice such as yours about managing Varroa throughout the year.
    Monitoring mite levels regularly, Treating with oxalic acid vapour when broodless in winter or whenever a brood break occurs during the active season, treating post harvest with Apivar the mite population.
    The result has been to keep Varroa kept under some sort of control and we have had only 2 colony losses in 10 years. Levels of DWV appear to be low – very few adult bees seem affected.

    I really hope that Prof Mackay’s team find their magic bullet!

    1. David Post author

      Hello John

      I fear the ecdysone approach will be neither available soon or cheap 🙁 . It might be effective. However, the miticides we have now, used appropriately – right time, right dose, right duration – are inexpensive (if not actually cheap!) and effective. I reckon my entire miticide cost per hive per annum is less than £7 i.e. about the same as a jar of honey.

      399 is the second highest number I’ve heard. I checked an area of London I used to live in and it was 432! The coordination requires communication and I certainly don’t think it would necessarily be easy. However, it also does not need to be absolute to be beneficial. I’m going to return to the subject in a future post as I think there’s more to the topic than I managed to cover in the post above.

      In the meantime, it sounds like you’re on top of things anyway. Two colony losses in a decade is good by any standard and – depending upon the number of colonies you’re running – expected from failed queens and ‘natural disasters’ anyway.

      6+ hives per square kilometre … have the bees done less well as beekeeping has become more popular? I’d start to be concerned about competition …


  11. Will Merryman

    Hello David,
    I had an experience this past season that supports all that you write about. A first for me. It goes like this. I live and keep bees on an island. I keep my bees in 5 different yards with 2/5 colonies per yard per Tom Seeley reccomendation. My northern most apiary had another beekeeper within flight distance. This yard always had higher counts than the yards south of there. Two years ago he wanted to sell me his bees and equipment, I had enough bees and equipment so passed. He sold them to a guy located near my southern most yard.
    Now comes the surprise!
    The northern yard this past season had very low kill counts for the first time ever (5/10 per colony) The southern yard had very high counts for a first for this yard. Ouch!
    Kill counts on the sticky boards there were in the multiple hundreds. Beyond my mental capacity to keep track.
    So the same bees with new owner who was mentored by former owner were and maybe are plaguing me here. They are still alive last warm spell and this week should be warm enough for a top down peek.
    I will say the broodless OA sublimation is the most important to perform as the kill counts stayed high due to my bees robbing out the weaker colonies.Honey bees are ruthless in their pursuit of survival. I really feel now that the varroa problem is exacerbated by the high colony counts of beekeepers with varying philospohies on how to keep bees. My guess is the colonies my bees robbed out prolly starved no way they could survive being a mite resevoir.
    Thank you for an excellent blog every week.

    1. David Post author

      Hello Will

      Pleased you enjoy the blog 🙂

      Very interesting observations … I guess you could abandon your southern apiary if the problems continue. At least you know things are ‘cleaner’ to the north again, so you could expand there.

      The importance of the winter broodless OA treatment is sometimes underestimated. If the bees are treated early enough in the autumn to properly protect the winter bees, the surviving mites will continue to reproduce in the late autumn (supplemented by mites acquired by robbing undoubtedly) and these mites are best targeted in midwinter with OA. If they’re not, then the higher mite levels at the beginning of the season will result in dangerously high mite levels in late summer.

      Every year I see people ‘bragging’ on social media that their OA mite winter mite drop was zero … the implication being that their bees are super-clean. Alternatively, my somewhat cynical view is that they probably didn’t treat early enough in the autumn to protect the winter bees … yes they have low mite levels, but they may still have high virus levels. The same beekeepers don’t tend to ‘advertise’ their winter losses in late March so I never know whether their bees were super-clean, or if my cynical view was correct.


  12. Colin

    Thank you David, valuable work. And thank you to the enlightened beekeepers of Arran for enabling it.

    My association does an excellent job, including coordinated bulk purchase of feed and jars at a discount. Perhaps the miticide manufacturers could also be interested in providing bulk purchase discounts too. It would be in their own interest of course, but could assist any associations in the task of motivating members to coordinate. I will investigate.

    1. David Post author

      Hello Colin

      I know the that Beefarmers Association get some miticides at a discount. Whether an individual association would have the buying power, I don’t know. Absolutely no harm in asking though.


  13. Peter George

    I may have missed it but didn’t get clear if the treatment coordination should be not just time-based but treatment type-based as well. Of course easier to insist everyone treats but since many try to rotate different treatments products to avoid resistance, product may be too much to fix. Perhaps we can at least group them into different processes (eg. Apiguard vs. Apivar vs. Api-Bioxal) Better to focus on converting the non-treaters nearby.

    Ultimately the solution is to escape to a more lonely region (oh yes, you’ve done that). Not easy for us southerners.

    1. David Post author

      Hello Peter

      There will be a follow-up to this post discussing the timing (how coordinated is coordinated?) and choice of treatments. In principle, if you knock all the mites down in an area simultaneously, whatever the method used, everyone benefits.


  14. Simon W Minford

    Just a quick comment on your colloquial slang usage. Northern Ireland has refined the use of Boggin’ and further developed it, and I think it particularly applies in this case. I would use the term “Thons’ Leapin’!!!” as it indicates a specific level of disgustingness 🙂

    Kind regards,


    1. David Post author

      Hi Simon

      I love the evolution of language … particularly slang. I think the first time I heard ‘boggin’ was in Reading in the late 80’s. There it didn’t mean disgusting, but instead meant large amount or huge. Perhaps it was only our research group, but it was in regular use for at least a decade until I moved to Scotland (where it, confusingly, meant something different altogether!).


  15. Ian Watkins

    The thought of trying to get our Association to coordinate mite treatment makes my blood run cold. 🤣

    1. David Post author

      Hello Ian

      I didn’t say it would be easy 😉 I’ll have a follow-up post on coordinated treatment and how it might be actually achieved (amongst other things) at some point in the future.

      You’ve got until early August to persuade them 😉

      Good luck!

  16. ian Robinson

    Hello David – apologies for being late to this post – just playing catch up after a busy few weeks. I am trying to get my head around your comments on DWV A & B towards the end of your post.

    You say…… “The island-wide replacement of one type of DWV with another was interesting, and has also been seen in other survey-type studies. There are suggestions that type B DWV persists in miticide-treated colonies, whereas the type A variant is dependent upon mites for sustained transmission and is lost (or at least significantly reduced) when mite levels are lowered. We have previously demonstrated that type B DWV replicates in mites, in contrast to type A DWV (Gusachenko et al., 2020).”

    If the type B DWV variant replicates in mites in contrast to type A DWV – why is it that the type A that is lost when mite levels are lowered. Am I missing something vital? Thanks

    1. David Post author

      Hello Ian

      I think it’s fair to say that we do not properly the understand the kinetics of virus replication of DWV. Since DWV B replicates in mites it probably reaches higher levels and is therefore more transmissible. In contrast, A probably gradually undergoes ‘dilution’ as the mites are removed, never reaching levels at which transmission is efficient. We’re just in the process of publishing a paper on some related processes in the mite transmission pathway and so I might have a follow-up post in due course.

      The replacement of A with B has now been observed multiple times, though in the case of Arran there’s always the possibility that feral colonies may have contributed …

      For day-to-day beekeeping all beekeepers need to be aware of is that mites are bad news, and that DWV – when transmitted by mites – probably accounts for the loss of the majority of colonies. The subtleties of A vs B is probably irrelevant other than to geeky science boffins 😉


      1. ian Robinson

        Thanks for the comments – bit of a geeky scientist myself (although not a virologist as you may have gathered) so I will keep a look out for a follow up post. Best wishes

        1. David Post author

          Hi Ian

          I think there are too many gaps in our understanding of DWV to make a properly coherent story (yet). This often isn’t unusual if a topic is relatively little studied. The other factor to consider is that DWV has largely been studied by either bee biologists or ecologists, with relatively few card-carrying virologists working on it. As a consequence the questions addressed, and the way they are tackled, perhaps don’t provide the most helpful answers.

          I’m sure things will improve … at some point 😉



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