Developing Varroa Resistant Bees: Steve Riley’s Guest Blog.

Steve Riley.

You’re in for a treat this week: Beelistener subscriber Steve Riley shares with us how he and team members at Westerham Beekeepers Association have progressed towards breeding varroa resistant bees. Professor Stephen Martin mentions this group in his presentations on developing resistance to varroa in honey bee colonies.

Steve is currently the chair of Westerham Beekeepers Association in England. He is also the education officer and involved with mentoring and teaching at the association’s training apiary. Steve is a member of Westerham’s Lead Bee Breeding Group which comprises proactive and dynamic beekeepers finding a way to produce varroa resistant bees using a team approach. His remit includes giving presentations on the varroa/honey bee relationship, and breeding varroa resistant bees for local distribution.

This approach, which Steve will explain, is a template for mainstream beekeepers at the club (and elsewhere) to use, and there is a growing appetite to retire from varroa treatments and get away from commercial beekeeping pressures. Zoom presentations have enabled a “shortening” of the distance between beekeepers, and somewhat addresses the dearth of useful education around varroa at beekeeper level in terms of how and when to treat.

A big warm welcome to Steve.

Identifying the Traits in Honey Bees That Manage Their Own Varroa Populations.

A group of like-minded Westerham Beekeepers gathered at the Carpenter’s Arms (those were the days) in the autumn of 2017 and started a project to “Identify honeybees that were resistant to varroa”.  We gave ourselves 5 years and set up a WhatsApp group to share ideas and experiences.

Illustration by Dan Peterson

Our apiaries populate the Kent / Surrey border in the south east of England.  With the inspirational Down House, Charles Darwin’s family home, nearby we sense the great man’s spirit encouraging us forward.

What started with 28 colonies across 8 apiaries has grown to over 100 colonies, including the involvement of other interested beekeeping associations.  The project has been a fascinating journey of learning, as we observed the bees transitioning to manage their mite levels. 

From here, it’s about knowledge sharing and giving “mainstream” beekeepers, like us, the confidence to have a go……

Scientific underpin to the project

Our interest in finding Apis mellifera honeybees that could adapt to living in balance with Varroa destructor was piqued by increasing amounts of research1 from leading bee scientists who articulated the strategies of already resistant bees, including: –

  • Hygienic behaviours, especially uncapping / re-capping, to disrupt mite reproduction
  • Grooming
  • Mite mutilation (Yes!!)
  • Naturally occurring brood breaks (e.g.; reproductive swarms) and good brood hygiene
  • Shorter capping period of worker brood (less time for daughter mites to mature)
  • Virus resistance

The research has taken place on untreated, long-lived survivor colonies, often feral.   We are very grateful for their excellent work, but clearly beekeepers were unlikely to carry out too much forensic research.  So, we needed to translate these findings into a workable protocol for beekeepers.

And, there were other hurdles to overcome: –

  • A deep- seated fear of not treating (“my bees will die”)
  • Much of the current education on the varroa & honeybee relationship is restricted to which treatments could be used at different points of the season
  •  A view that evolution / adaption couldn’t happen in our life-times (….it had)

PHASE 1: Cautious initial approach to avoid large colony losses

A strategy of stopping varroa treatments and putting the bees through natural selection seemed like too blunt an approach, especially at a beekeeping club.  Beekeepers are emotionally involved with their bees and large colony losses would curtail the project for all but the hardiest.  So, we went for a staged approach, starting with the replacement of the summer miticide treatment with a choice of biotechnical methods learned from Dr Ralph Büchler, whom we met at Gormanston in 2017.  We found that Queen Frame Traps (used July-August) are remarkably efficient at removing mites; better than any combination of miticide treatments – more details at

We also dropped the mid-winter treatment so that bees could be judged in the spring – this time of year provides many clues as to how or whether adaption is likely to occur – more on that later.

Following the first winter/spring, 26 out of 28 colonies came through in good shape using these biotechnical methods.  Phew!  Good start.

The fear of not treating had been overcome; we understood how the methods worked and were ready to move on to “no beekeeper intervention”.  After all, these methods were still taking the varroa problem away from the bees and not testing their genetics.

Phase 2: Identifying varroa resistant traits in our honeybees

The bee scientists identified some tangible traits of adapted bees that beekeepers could easily spot during their normal inspections: 

>> Uncapping / recapping            

>> Removal of infested brood

>> Grooming / mite mutilation

Uncapping / recapping:  Who’d have thought that there was so much uncapping and recapping of worker brood going on right under our noses?  Between 40-60% of sealed worker brood cells were being checked by nurse bees for varroa.  On uncapping a cell, the foundress mite would leave and mite reproduction would be halted.  Interestingly, this is a strong trait of “Resistant” bees that have adapted to varroa, but less so of “Susceptible” bees, which depend on treatments to be kept alive.

Uncapping is easy to spot – we train our first season beekeepers to understand what is going on.  It occurs at between the white to pink-eyed stage of worker pupae development.

Photo by S Riley- Westerham Beekeepers.

The diagram below illustrates how the uncapping of the worker cell by the bees interrupts the varroa reproduction process at a crucial stage.


Removal of infected pupae:  Again, another easy spot for beekeepers.  On the insert board under the open mesh floor, chewed out body parts can be seen where infected pupae have been removed.  Seeing this in February & March, indicates that the over-wintered mites are being stopped from reproducing.  This will decrease mite numbers during the spring brood build-up and most importantly, demonstrates that the right bee genetics are in place for the season.

Picture taken 5th March 2021 by Steve Riley Westerham Beekeepers.

Keen observers at the entrance will sometimes see white pupae being flown out.  During the winter, they are unceremoniously dumped outside of the hive entrance.  Top hygienic behaviour.

We are grateful to Professor Stephen Martin and his team for the following diagram illustrating the benefit to the colony of the bees removing infected pupae and interrupting the foundress mite from reproducing.  A small sacrifice stops a large army of varroa and parasitised bees being produced. 

Grooming / mite mutilation:  Little harder to see for beekeepers, but there are add-ons to smart phones that would give sufficient magnification (20-30x).  The picture below from one of our colonies illustrates the damage that bees will do to mites. 

Spring monitoring provides important clues

During strong brood development in the spring, mite levels indicate whether the bees prioritise the interruption of varroa reproduction – are the right genetics in place?  Wide differences in performance inform breeding decisions, as shown in the graph below, which measured accumulative mite drop.  The colonies were on 7-9 frames of brood in a National brood box.

Phase 3: Breed from varroa resistant bees

This is our current breeding protocol which is tweaked as we learn.  It combines the indicators for varroa resistance and good health, natural selection and temperament.  As part of the evaluation loop, varroa observations (uncapping, mutilation, mite levels) are recorded on our hive record cards.  Our best colonies also receive additional drone comb to influence and improve the local genetics.

Phase 4: No beekeeper intervention for varroa

Finally….letting go.  This can be quite hard to do as a beekeeper, as for many years, you had convinced yourself that you were their saviour…..

Here’s a colony entering its third season without any beekeeper intervention for varroa. 

Whilst we appreciate that the project is in its early days, seeing the bees controlling their mite population is very encouraging.

How we monitor mite levels

Through the research phase of the project, it felt important for us to gain a deeper understanding of the seasonal varroa populations in our hives and whether the observed resistance traits from the bees (e.g., uncapping) had an effect.

Some of us opted for labour-intensive mite counting (every 2 days) on an insert board under an open mesh floor.  We saw a number of advantages over the 300 bees “sugar-shake” or “alcohol-wash” methods: –

  1. The mite level drop was from the total colony, so statistically stronger
  2. Could continue through the 5-6 months of late autumn/winter when the hives are closed
  3. Chewed out pupa parts could be seen (identifying hygienic behaviour)
  4. Non-invasive & no bees harmed
  5. Source of other information e.g.; lines of bees from wax clippings, or honey being accessed

One of the team pops the insert board in for 3 days a month for her counts, which gives a solid guide. So, it doesn’t have to be too labour intensive.

Colony outcomes

There’s a natural fear when you start off down this road, as most beekeepers have only known the “treat for varroa” environment.  So far, the outcomes have surpassed our best hopes.

Season /winterVarroa managementColony outcomesColony lossSouth East losses (BBKA)
2018 / 19Biotechnical26 / 287%9%
2019 / 20Bees33 / 3711%22%
2020 / 21Bees45*/ 51*12%*TBC

The results are those of the Lead Breeding Group, spread out across 8 apiaries and some 50 square miles in largely unconnected apiaries. 

We raise our own queens and have done for a number of years.  THIS IS IMPORTANT for adaption to occur.  Do not disturb the locally adapted genetics by bringing in “outside” bees.  With survival ratios of some 85-90%, the genetics of mite resistance strengthen year on year from making increase from the best stocks (and re-queening the worst), but also from the drones, who are a clone of the queen’s genetics and in circulation locally.

Contrast this with the prevailing cycle of breeding.  “Mite Susceptible” bees depend on treatments to survive and weak genetics are promoted.  Worse than that – the varroa which are tough enough to survive miticide treatments are the new breeding stock.  So, the mites get stronger…… and the bees get weaker.

This cycle can be reversed by introducing “Varroa Resistance” as a breeding criterion.  Hint, hint breeders

Honey yields about the same

Honey yields from our colonies seem similar compared with our previous varroa regime and with treating beekeepers in the area (weather and OSR crops being the main delta).  Why could this be?

With not using miticides, the beekeeper has complete flexibility of when to take off honey, which can be beneficial.  From a varroa perspective, logically, there is a trade-off between two negative effects on the colony: –

        “Mite Resistant” bees removing varroa infected pupae or spending time grooming


   The build-up of parasitised bees through the foraging season ahead of needing treatment

Virus tolerance requires further investigation

“It’s not the mites that kills the bees, it’s the viruses they vector.” 

This is often heard in beekeeping but may not be true for naturally resistant bees.

Some of our colonies get through winter and perform well the following season despite having had very large autumn mite loads.  For example, one colony in the group had a mite drop of 150 per day in late summer/early autumn in 2019 and a similar number again at the same time of year in 2020.  But the mite drop is low at the end of the winter, currently running at 1 per day.  These bees are surviving and produced the largest honey yield in the apiary last year.  There are other similar colonies in the group with high mite profiles.  Something interesting is going on which we’d like to understand.

Are “Mite Resistant” bees also more tolerant of the viruses that varroa vector?  And, of other viruses generally?  Research4 from the Swedish University of Agricultural Sciences suggests that virus tolerance may be generic and also have a genetic heritable component.  This could explain why untreated resistant stocks can survive year after year.

Another school of thought is that Deformed Wing Virus, the main virus vectored by varroa, is more virulent when “injected” directly into a larvae / pupa by the mite, rather than transmitted by other means.  As mite loads fall, then virus virulence diminishes……………..

We await further research on virus resistance.

*    *    *    *    *


We have a better, but still incomplete understanding of how our bees are managing their mite populations. 

Background adaption to varroa, aided by some natural selection from long standing feral or unmanaged colonies, has occurred in the almost 30 years since varroa arrived in the UK.  We strongly suspect that varroa resistance is more widely spread than in our heavily populated area of the south-east of England.  Just needs us beekeepers to start looking……

Key lessons that we have learnt through our project are summarised in the Appendix.

We had better finish with the great man:

“It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change” – Charles Darwin, 1809.


Thank you to Dr Ralph Büchler for mentoring the project.  We are grateful to Professor Stephen Martin, particularly for his input over viruses and also to Dr Jeff Harris, for his understanding on VSH bees.  Thank you also to Clive and Shân Hudson for their friendship & encouragement and for so willingly sharing their beekeeping experiences


1 Natural Varroa mite-surviving Apis mellifera honeybee populations.  B Locke 2015

2 “Sustainable Varroa Management” lecture by Ralph Büchler at the National Honey Show, October 2019 (Research including queen frame trapping – 47 minutes in)

3 More details

4 “Increased Tolerance and Resistance to Virus Infections: A Possible Factor in the Survival of Varroa destructor-Resistant Honey Bees”, Barbara Locke et al, Swedish University of Agricultural Sciences, June 2014

“Disentangling host-parasite-pathogen interactions in a varroa-resistant honeybee population reveals virus tolerance as an independent, naturally adapted survival mechanism”, Thaduri et al, Swedish University of Agricultural Sciences, April 2019


20 things we have learned:

Uncapping interrupts varroa reproduction (white to pink eyed stage)

Removal of body parts of infected pupae can be seen on insert boards under the open mesh floor

Damaged mites bring a smile to the beekeeper

Hive record cards to include section on varroa observations (numbers, mutilation, uncapping)

Evaluate queen performance in relation to varroa and act on it

Raise your own queens

Re-queen colonies with poor varroa performance (shortens route to varroa resistance)

Encourage drone production from your resistant stocks  -> influence local genetics

Encourage neighbouring apiaries down the same breeding path

Locally adapted bees only – don’t disturb local genetics with “outside” bees

Brood breaks, say from artificial swarming, are a hygienic defence from all brood diseases and varroa

Stopping treating is a bit scary at first

Biotechnical methods can overcome the initial fear of stopping treating; a cautious approach

Start with a small number of colonies, where uncapping has been observed

Work together in a like-minded (WhatsApp) group.  Party like bandits when things go well and act as a cooperative if things go wrong   (Thank you Bartek for the spirit of that idea)

Let the bees eat their own honey, especially ahead of, and over winter

Take a 3 year view

Capturing swarms, from long standing feral or unmanaged colonies, are a good source of resistant genetics

Resistant bees can be any colour

Be prepared for “humble admiration” when your bees manage their mite populations


Thank You, Steve.

22 thoughts on “Developing Varroa Resistant Bees: Steve Riley’s Guest Blog.”

  1. A great read Ann. I now have 5 apiaries so I will start slow and try this method. We should add mite drop to the spreadsheet. Fred

    1. I’m glad that you liked this read, Fred. I find it fascinating and inspiring. Feel free to share this blog. Yes we should add the count to the chart, Fred. I have a weekly varroa count underway at the moment but not sure how to incorporate that in the spreadsheet.

  2. The best thought out and most clearly described treatment avoidance program I have read about. It would be great if there was a will from some people to try this in the IV12 postcode area. 🙂

    1. Yes, I agree with you there, Peter, on both counts. I’m hopeful for change here too. If there is a willingness to hear about new ways of doing things, Steve will speak to local associations within the IV postcode!

  3. It is lovely to have all this info in one place and to see the progress made. The best things of all must be the co-operation, trust and friendship between members of the group. Congratulations, Steve xx

  4. Greetings,

    I am so glad to have found your site as I have been doing TF for two decades or more but with different variables, such as an infusion of AHB’s in my area, which are not that aggressive. I have been collecting ferals and never felt the need to treat against v. mites. I am trying to do now with SHB’s, almost ubiquitous in US. Not an advertisement, but you can see some pics of my feral survivors here:

  5. Lots to approve of here just hope it filters through to the beginners courses where we pick up most of our questions as well as our answers.

  6. So well put together and this covers all of the points that I have learned from experience and the researchers in Ireland who are now doing a study on resilient bees. I last treated in 2016 coincidentally at the same time as 2 other friends in different areas, mainly because we were unsure about things. Winter losses have been falling year on year, so far this year I have one weak nuc out of 45 colonies down from 2 losses from 35 and 3 from 28 the year before. Our bees are LOCAL and originally caught and bred from FERAL swarms where possible. Good luck with the venture. One comment about those with the very high short term mite loads but high production. I have seen this but later in the year when I regularly counted the mites and I think it is from robbing out weak or dying colonies. when the robbing stops the mites are killed off and back to normal!

    1. Thank for responding, Alan, and for sharimg your mostly positive experiences. Reinfestation seems to be a problem even if you have resistant bees. I thought it was disappointing to learn from Professor Martin that resistant bees moved to another area didn’t do well there. All the more reason to only work with very local bees.
      Steve did a great job of communicating all of this information about their system in such a comprehensive way making it easy for others to follow.

      1. Hi Anne, Thank you for taking the time to reply. I would like to take the opportunity to add some more comments which relate to our discussion and the following one between Thomas Seeley and Steve Riley which might be of interest to everyone.
        Our ‘mite bombed’ hives daily drop levels were taken while there was still a large amount of brood in the hives but it was admittedly dwindling. I have noted recently that our Irish bees tend to have brood breaks on and off, usually due to weather, up until April which is not surprising but we also tend to have one in many colonies (confirmed by much more experienced beekeepers than me) in July, just before the harvest. I think that this is to allow room for the nectar to come into the brood space in the daytime before being moved up overnight. Further to this I usually only do a cursory brood check as I clean off the bottom boards and rate them between 0, low 1-2 per day, medium 2-4 and high, over 6 per day. Rarely do they go above 2 per day and do not show an increase at the summer brood brake. Food for thought here and still baffling how they cope with the exceptionally high autumn mite drops whatever the cause or reason.
        Regarding our sets of bees, unlike the Kentish group we are 3 individuals and are separated by 25 to 40 miles from each together with mountains, estuaries and cities separating us and it is unusual that we move bees between us. The bees were virtually all caught in local feral swarms ie. within 10 to 15 miles or our bases. Our locations are rural and two of us have our own bees in areas of about 100 sq. miles each
        My reasoning for the success of these bees being able to deal with the varroa is that not only are our queens able to produce resilient bees but, obviously to me, the drones in the area are also capable of the same being from survivor stock. Incidentally my neighbour has bred queens from a ‘live and let die’ experiment. If I remember correctly about 3 out of 25 survived so my bees will also be mating with some of these as well as his other bees and local feral survivor stocks. The point to take from this is that in my opinion the bees might not do well if moved to other areas as Professor Martin has observed. I assume this is because of the lack or resilient bees or over treated bees in some other areas. We still however have not moved any bees to different areas but will start to do so this year as part of a queen rearing program by NIHBS and I will follow up with some colleagues to see if our bees improve their local bees over the next few years.
        Another point to note is that a very experienced beekeeper who is base only about 10 miles away but whose apiaries are all over 10 miles away from me has always treated his bees and is in a situation where he has to treat or lose the colonies.

        1. Thank you for all this additional information, Alan. It is most valuable as is this blog and all the comments which makes a goldmine of pooled knowledge to help others. I think that we will all be waiting to see what happens when you move the bees so please keep us updated if you have time.

  7. Thank you for sharing your group’s methods for and progress with keeping bees without treating colonies with miticides. Your results are extremely encouraging, esp. because it seems that your group’s members are only a subset of the Westerham Beekeepers group. Can you give us an estimate of the % of the beekeepers (or the % of the managed colonies) in your area that are participating in your program?
    Incidentally, when I have monitored mite levels in colonies (not treated with miticides) by counting the mites caught on sticky boards, I too have seen high counts in late summer-early autumn (October), and at first I feared these colonies were doomed, but like you I have found that they survived winter just fine. I suspect that what is going here is that colonies have little or no sealed brood at this time of year, so all the mites are vulnerable to the grooming of the bees, and as a result these late-season mite-drop counts can give us a “distorted” picture of the colonies’ mite populations .

    1. Hi Tom,
      thank you for your observation. The colony featured with the high mite count is under further investigation. We estimate that during the 3 months August-October, mite drop was over 9,000. There does seem to be an extra ordinary level of hygienic behaviour going on in preparation for winter, together with fewer cells for mites to occupy, as you note. We are comfortable with those conclusions. Here’s the bit that is bugging us. It seems very likely that every worker larvae/pupae of those winter bees (laid through to the end of October) will have been parasitised. So how are they surviving winter? This is taking us down a virus tolerance road, or somewhere else….

      Like some other colonies in the group with a high mite profile, they are yellower bees. Our darker bees tend to be more active in controlling mite levels through the year, which are easier on the beekeepers’ nerves, but show no better or worse winter survival, or indeed foraging ability. Maybe over a longer period, a pattern will emerge from their differing strategies.

      Immediately around us, we dominate the local genetics. In the 50 sq miles under observation, we probably have 20-25% influence. What’s interested us is the lack of geographic connectivity between surviving colonies; we are tempted to assume a level of background adaption has occurred where beekeepers have raised their own bees and not disturbed the local genetics. Newer beekeepers are joining the project from further afield, broadening the area to c.100 sq miles, which will inform or bust the adaption assumption.

      We are also hearing of other similar projects underway. It will be the not-for-profit hobbyists in the UK who will facilitate this bee-led evolution!!

      1. Hi Steve,
        Regarding the puzzle of how colonies can survive when it seems that every brood cell is probably infested with a Varroa mite, I don’t know for sure, but perhaps colonies are surviving winter with long-lived “winter bees” that were reared before most or all the cells of capped brood were infested with Varroa. Research conducted in Canada by Gard Otis and Heather Mattila looked at what triggers the production of long-lived worker bees and they found that this starts when the availability of pollen declines. Where they worked, in Ontario, they found that winter bees began to appear in colonies in late August, which is much earlier than I would have guessed). I dons’t know your situation, but perhaps in your colonies, too, enough winter bees are reared before the
        Varroa mite/brood cell ratio skyrockets.
        And BTW, I agree, it is the not-for profit beekeepers who are showing the way forward. They can step off the chemical-treatment treadmill without getting seriously hurt.

        1. Thanks Tom for those thoughts and we’ll take a look at the research. We have assumed that the “cleaned out mites” were in brood cells and around the brood nest area during the last main summer flow which finishes around the end of July here. Our hypothesis is that these colonies exhibit strong hygienic behaviour once they have secured their winter stores, which alleviates nurse bees from receiving nectar and processing duties. The winter bees’ longevity needs further work….!

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