What the evidence shows, and what it doesn’t

Since the late 1990s, varroa resistance has resurfaced repeatedly — Africanised bees, the Gotland survivors, hygienic breeding programmes, and more recently treatment-free narratives — each time framed as a solution, and each time constrained by ecology, genetics, and scale. Talks promise it, social media celebrates it, and survivor colonies are held up as proof. And yet, whatever people may claim, we have not actually got widespread varroa resistance in our bees.

Here are some examples from the past:

Late 1990s To Early 2000s

Once varroa had spread globally, people looked for populations of honey bees that appeared to cope with the mite. There were Africanised bees and Russian Primorsky stock, which showed lower mite growth rates, prompting optimism that genetics alone could solve the varroa problem. As European honey bees were rapidly dying, and beekeepers were deciding to “call it a day”, the great hope was that some bees had already found a solution. The controlled field trials of Rinderer¹ et al. (2001) demonstrated heritable resistance traits under specific conditions, but not their universal transferability. Similarly, a study of Africanised² bees showed several resistance mechanisms.

Both bee types were difficult to work with (defensive) and were not big honey producers (hardly ideal for those trying to earn a living from bees). Inevitably, some UK beekeepers wanted to import some Primorsky bees but, as far as I know, there was no legal way for this to be done.

Mid 2000s (2005 – 2010)

A population of honey bees on Gotland³ in Sweden was left untreated in a “Live and Let Die” approach. There were massive losses, but eventually survivor colonies showed success at reducing the varroa mites’ reproduction. This seemed to validate “treatment-free” beekeeping as a viable path, and the study has been quoted endlessly ever since. However, this was difficult to replicate, especially in the UK because it required an isolated population and a tolerance for high losses.

The Gotland ‘Bond’ survivors are a genuine example of reduced mite reproductive success, but they also passed through a severe genetic bottleneck⁴. Genetic data show a marked loss of diversity after selection, raising concerns about long-term resilience in small, isolated survivor populations. There is a danger of “throwing the baby out with the bathwater”, to use a quaint old phrase – loss of genetic diversity, defensiveness, low productivity – it’s not sounding that great so far.

Later, varroa sensitive hygiene (VSH) and suppressed mite reproduction (SMR)⁵ became headline traits, with many breeding programmes springing up to select for them. Breeders liked these because, as long as they controlled mating using isolated stations or instrumental insemination, they could show a clear and measurable improvement over time, while also preserving desirable traits such as productivity.

The main problem with targeting one particular resistance trait using breeding is that the way bees manage varroa in their colonies involves multiple different behaviours, not just one. There is also a strong environmental component. And, of course, there is the evergreen challenge in the UK that with open mating any traits can be lost in the following generation.

Late 2010s

“Natural selection will fix it if we stop treating.”

There has been a surge of treatment-free advocacy driven by social media, YouTube, and experiences of some (temporary?) successes by small-scale beekeepers. This is often framed as a morally superior stance than the traditional methods used by “old-fashioned” beekeepers like me, which involves treating. Even though many commercial bee farmers in the UK have losses of around 10%, typically using organic treatments like oxalic acid as part of integrated pest management (IPM), one justification for the trend is that mites are becoming resistant to treatments. In other words, if treatments are failing, why use them? I have written about this at length. Treatments are working just fine, by the way, for me anyway.

I believe that people mistake colony survival for varroa resistance. They mistake varroa tolerance for varroa resistance. They also, probably, understate their losses, but I think many beekeepers are prone to that.

The Pattern

So, over decades, the pattern followed goes like this:

1. A real biological signal is observed

2. It is amplified into a general solution

3. Constraints are downplayed

4. Replication fails at scale

5. The idea goes quiet — then re-emerges, reframed

What Scientists Mean by “Varroa Resistance”

Varroa resistance describes heritable characteristics that reduce mite population growth, across generations, without intervention. That definition immediately excludes many things commonly labelled as resistance in beekeeping circles.

Resistance ≠ Tolerance ≠ Survival

Tolerance: colonies survive despite high mite loads, often by compensating behaviourally.

Survival: colonies persist long enough to be noticed, sometimes due to chance, location, or reduced exposure.

Resistance: colonies actively suppress mite reproduction or transmission in a way that can be selected and stabilised.

Most untreated colonies fall into the first two categories. Peer-reviewed studies consistently show that resistance is multi-trait⁶, population-level, and slow to stabilise. No credible programme has demonstrated a single “magic” behaviour that solves varroa on its own.

What Resistance Traits Actually Exist?

Several traits do reduce mite reproductive success, but none operate in isolation.

Documented resistance-associated traits

• Varroa-sensitive hygiene (VSH) – targeted removal of infested brood

• Suppressed mite reproduction (SMR) – reduced mite fecundity

• Grooming behaviour – removal or damage to phoretic mites

• Brood interruption – breaks in reproductive cycles

• Reduced post-capping duration – less time for mites to reproduce

Crucially, these traits:

• Vary widely between colonies

• Are influenced by environment and nutrition

• Can be diluted rapidly through open mating

A colony expressing one trait in one season does not mean you have a resistant population. Without mating control, the genetic signal decays fast, typically within a single generation.

Resistance Is Real

Resistance is real, but it has emerged only under exceptionally strong selection pressure. There’s the Gotland project, Norwegian survivor stocks, and various cases featuring isolated populations. There are some uncomfortable downsides, such as very high initial losses, long timelines, and the requirement for geographic isolation (not easy in the UK). The problems facing UK beekeepers who want to breed varroa resistance into honey bees include:

• High apiary density, so NOT an isolated population, and constant mite (and bee) immigration from outside
• Open mating almost everywhere, resulting in rapid genetic dilution of any resistant traits that may emerge
  

What’s more, there are rarely acknowledged tradeoffs – resistance is not “free”. Traits like hygienic behaviour and brood sacrifice divert resources away from honey production. Thomas Seeley’s work⁷ highlights that wild-type survival strategies prioritise persistence, not productivity — a perfectly rational strategy for bees, but a problematic one for beekeepers.

For UK Beekeepers

Just because something is challenging does not mean it’s not worth pursuing. I am not against people properly following a path of working towards varroa resistance in honey bees. However, I am concerned that expectations may be unrealistic, at least in the medium term. From my perspective, trying to progress towards resistance is an admirable goal. Reducing treatments from twice to once per year is a great thing. What I am against, is being sloppy and leaving bees to struggle and die, especially when effective treatments are available. The plan⁸ set out by Randy Oliver seems to be the most promising one in my opinion.

Rigorous measurement of mite infestation, using a reliable method (mite wash using alcohol or detergent), on all colonies on a regular basis is the only way to be sure. That is a huge amount of work. It’s important to also measure the rate of increase in mite population, as some colonies may show an ability to slow this down, whereas in others it can run away. With our high apiary density and open mating, the goal of a stable treatment-free population of honey bees in the UK is very unlikely to be achieved. However, getting down to a single oxalic treatment in winter would be a massive achievement, especially if the money saved on treatments is not eclipsed by decreased revenue from lower honey crops.

It is vital to put as much care into the drone side of the breeding equation as the queen side. That is the big challenge with a high number of bees in the area and open mating – how can you control which drones mate with your queens? Having said that, I raise queens using open mating, and my bees have improved over time. There are setbacks, and the way to deal with the occasional defensive or unproductive colony is to requeen it with something better, rather than let its drones enter the mating pool.

If the UK is to make progress, it will do so through measurement, coordination, and realism, not slogans.

References

1. Resistance to the parasitic mite Varroa destructor in honey bees from far-eastern Russia Thomas E. Rinderer, Lilia I. de Guzman, G.T. Delatte, J.A. Stelzer, V.A. Lancaster, V. Kuznetsov, L. Beaman, R. Watts and J.W. Harris Apidologie, 32 4 (2001) 381-394 DOI: https://doi.org/10.1051/apido:2001138
2. Susceptibility of European and Africanized honey bees (Apis mellifera L.) to Varroa jacobsoni Oud. in MexicoErnesto Guzmán-Novoa, Rémy Vandame and Miguel E. ArechavaletaApidologie, 30 2-3 (1999) 173-182 DOI: https://doi.org/10.1051/apido:19990207
3. Survival of mite infested (Varroa destructor) honey bee (Apis mellifera) colonies in a Nordic climate Ingemar Fries, Anton Imdorf and Peter Rosenkranz Apidologie, 37 5 (2006) 564-570
   DOI: https://doi.org/10.1051/apido:2006031
4. Lattorff HM, Buchholz J, Fries I, Moritz RF. A selective sweep in a Varroa destructor resistant honeybee (Apis mellifera) population. Infect Genet Evol. 2015 Apr;31:169-76. doi: 10.1016/j.meegid.2015.01.025. Epub 2015 Feb 4. PMID: 25660040.
5. Harbo, J. & Harris, Jeffrey. (2005). Suppressed mite reproduction explained by the behaviour of adult bees. Journal of Apicultural Research. 44. 21-23. 10.1080/00218839.2005.11101141.
6. Breeding for resistance to Varroa destructor in Europe Ralph Büchler, Stefan Berg and Yves Le Conte Apidologie, 41 3 (2010) 393-408 DOI: https://doi.org/10.1051/apido/2010011
7. Seeley, The Lives of Bees https://theapiarist.org/the-lives-of-bees/
8. Selective Breeding For Mite Resistance https://scientificbeekeeping.com/selective-breeding-for-mite-resistance-walking-the-walk/