Why these populations attract such interest in beekeeping

Since the arrival of Varroa destructor, beekeeping has relied heavily on active varroa management. Yet a number of Apis mellifera populations have been described as capable of persisting durably without treatment, or with a greatly reduced treatment burden. These cases naturally attract attention, as they demonstrate that long-term survival under varroa pressure is not biologically impossible.

The interest in these populations does not, however, rest on the idea of a "miracle bee". Their value is primarily scientific and practical: they function as natural experiments. They make it possible to observe which traits, which colony dynamics, and which ecological contexts can contribute to slowing the growth of the varroa mite.

For beekeepers in central Europe, the right question is therefore not: "Does an immunised bee finally exist?", but rather: "What do these documented cases actually show, and how far can their lessons be transposed to a managed, dense apiary exposed to re-infestation?"

Surviving population, varroa tolerance, and resistance — not to be conflated

The first point to clarify is terminological. A naturally surviving population is not simply a single "strong" line, nor is it proof of immunity.

It refers to a group of colonies that, in a given context, manages to keep the varroa infestation at a level compatible with its persistence.

This survival may rest on several realities that must not be conflated: reduced reproductive success of the parasite in capped brood, certain traits of the brood itself, worker bee behaviours such as hygienic behaviour or recapping, better management of colony dynamics, or lower susceptibility to damage associated with the varroa-virus complex. In practice, observed survival is almost always multifactorial.

It is therefore more accurate to speak here of survival, sometimes of varroa tolerance, and only with caution of resistance. The word "immunity" should be avoided: these colonies do not live without varroa; they live with a more favourable balance than ordinary colonies.

Three reference cases — and a useful counterpoint

Gotland, in Sweden, is the emblematic case. But it must be recalled at what cost this trajectory emerged: the initial experiment began with 150 colonies left untreated, and winter losses reached very high levels before a later stabilisation phase — approximately 76% mortality after the third winter and 57% after the fourth. The surviving colonies subsequently observed were smaller and showed lower varroa reproduction than susceptible colonies. In other words, Gotland illustrates host-parasite adaptation under very strong selection pressure — not a simple, immediately transferable solution.

The Norwegian population described by Oddie and colleagues is particularly interesting for European beekeeping, as it involves a managed but untreated population for many years at the time of the study. The authors observed lower infestation levels and a reproductive success of varroa reduced by approximately 30% compared to local susceptible colonies, without grooming or VSH alone being sufficient to explain this survival. This case is valuable, but it too remains linked to a local selection context and specific conditions.

The Avignon case is essential in the French-language context. Le Conte and colleagues documented colonies surviving in France without varroa suppression measures; some of the original colonies had survived more than 11 years without treatment, and the mean survival duration observed in the study was 6.54 ± 0.25 years. Honey production, however, remained significantly lower than in treated colonies by a factor of approximately 1.7. This point matters: survival does not imply absence of trade-offs.

The Avignon case must nonetheless be read with caution. A subsequent critical analysis highlighted that this population would probably not have persisted through natural selection alone: varroa dynamics remained compatible with parasite growth, and the maintenance of the stock also relied on prolonged artificial selection and regular multiplication of the best colonies. Here too, this is less a case of perfect spontaneous autonomy than of a system progressively oriented towards greater survival.

Arnot Forest, in the United States, is more useful as a counterpoint than as a direct model. This case underscores how much the ecology of the environment matters: feral colonies, greater distances between nests, a different renewal dynamic, limited input from neighbouring apiaries. It shows above all that a population can become self-sustaining under very particular conditions, but it does not provide a recipe directly transferable to managed beekeeping in central Europe.

What these populations suggest about survival mechanisms

The most robust finding is probably the following: in several surviving populations, the reproductive success of varroa is lower than in susceptible colonies.

In other words, the parasite is less successful at producing viable offspring in capped brood. This result has been demonstrated in both the Swedish and French cases, and subsequently confirmed in the Norwegian population.

More recent work nevertheless cautions against an overly simple reading. Part of this difference appears to derive from traits of the brood itself, and not solely from the behaviour of adult workers. Comparative studies have shown that certain brood characteristics can, on their own, contribute to reducing varroa reproduction, without excluding a parallel role for adult bee behaviours.

Adult bee behaviours nonetheless remain important. Recapping, certain forms of hygienic behaviour, and other colony responses can contribute to disrupting the parasite's reproductive cycle. The literature does not, however, support the idea of a single, universal, and easily measurable mechanism. It is rather a combination of partial traits, paired with a colony dynamic compatible with survival.

Finally, it must be kept in mind that varroa does not act alone. The actual health burden of the parasite also depends on the viral context and the overall state of the colony. Surviving populations do not escape varroa; they appear above all to contain its growth more effectively and, in some cases, to tolerate its consequences more durably.

What cautious lessons can managed beekeeping in central Europe draw?

The first lesson is that it is worth reasoning in terms of local adaptation.

Surviving populations suggest that selection based on colonies that remain lastingly viable in a given environment makes more sense than an abstract search for the "right line" valid everywhere.

The second lesson is that great caution is needed in choosing selection criteria. Reduced varroa reproduction is a promising indicator, but its measurement remains technically demanding. Recent methodological studies show low repeatability and reproducibility of these measurements, as well as limited correlation with overall colony infestation levels. In practice, this means that this type of assessment can guide selection, but must neither be oversimplified nor used as the sole criterion at the apiary.

For beekeepers, the practical takeaway is therefore not to count on a simple test that would allow rapid identification of "resistant" colonies. The message is rather that selection for survival requires time, a coherent local context, rigorous observation, and great caution in interpreting results.

The third lesson is that a realistic strategy for managed beekeeping consists less in "copying nature" than in integrating certain insights into a reasoned approach: serious varroa monitoring, limiting situations that favour re-infestation, careful selection for colony viability, and maintaining health responsibilities towards the apiary and neighbouring beekeepers.

Naturally surviving populations do not say that treatment has become useless. They show above all that total dependence on a purely corrective approach is probably not the only long-term path. Their main contribution is to open avenues for a beekeeping that seeks greater robustness without abandoning rigorous health management.

Conclusion

Naturally surviving populations demonstrate that durable survival in the face of varroa can emerge in Apis mellifera. They also indicate that this survival rarely rests on a single trait. It results rather from a combination of biological mechanisms, colony dynamics, and favourable ecological conditions.

For managed beekeeping, the essential lesson is therefore not the abandonment of treatments, but the need to better understand what makes some colonies more durable than others. These populations do not provide a ready-made solution. They serve rather as a compass: they remind us that the varroa question cannot be reduced to a product, an acronym, or a myth, but comes down to the concrete balance between parasite, bees, environment, and beekeeping practice.

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See also:

• The colony and varroa: resistance, resilience, and the limits of selection
• From the varroa cycle to assessment methods
• Development and dynamics of bees and varroa throughout the year
• Practical Guide: 2.8 Varroosis
• The recommended varroa treatment strategy increases colony survival
• Varroa mite infestation impacts the thermal regulation of honey bee colonies

Selected references

Frey, E., & Rosenkranz, P. (2014). Autumn invasion rates of Varroa destructor (Mesostigmata: Varroidae) into honey bee (Hymenoptera: Apidae) colonies and the resulting increase in mite populations. Journal of Economic Entomology, 107(2), 508–515. https://doi.org/10.1603/EC13381

Le Conte, Y., de Vaublanc, G., Crauser, D., Jeanne, F., Rousselle, J.-C., & Bécard, J.-M. (2007). Honey bee colonies that have survived Varroa destructor. Apidologie, 38(6), 566–572. https://doi.org/10.1051/apido:2007040

Locke, B. (2016). Natural Varroa mite-surviving Apis mellifera honeybee populations. Apidologie, 47, 467–482. https://doi.org/10.1007/s13592-015-0412-8

Locke, B., & Fries, I. (2011). Characteristics of honey bee colonies (Apis mellifera) in Sweden surviving Varroa destructor infestation. Apidologie, 42(4), 533–542. https://doi.org/10.1007/s13592-011-0029-5

Locke, B., Le Conte, Y., Crauser, D., & Fries, I. (2012). Host adaptations reduce the reproductive success of Varroa destructor in two distinct European honey bee populations. Ecology and Evolution, 2(6), 1144–1150. https://doi.org/10.1002/ece3.248

Oddie, M. A. Y., Dahle, B., & Neumann, P. (2017). Norwegian honey bees surviving Varroa destructor mite infestations by means of natural selection. PeerJ, 5, e3956. https://doi.org/10.7717/peerj.3956

Scaramella, N., Burke, A., Oddie, M., Dahle, B., de Miranda, J. R., Mondet, F., Rosenkranz, P., Neumann, P., & Locke, B. (2023). Host brood traits, independent of adult behaviours, reduce Varroa destructor mite reproduction in resistant honeybee populations. International Journal for Parasitology, 53(9), 527–535. https://doi.org/10.1016/j.ijpara.2023.04.001

Seeley, T. D., Tarpy, D. R., Griffin, S. R., Carcione, A., & Delaney, D. A. (2015). A survivor population of wild colonies of European honeybees in the northeastern United States: investigating its genetic structure. Apidologie, 46, 654–666. https://doi.org/10.1007/s13592-015-0355-0

van Alphen, J. J. M., & Fernhout, B. J. (2020). Natural selection, selective breeding, and the evolution of resistance of honeybees (Apis mellifera) against Varroa. Zoological Letters, 6, 6. https://doi.org/10.1186/s40851-020-00158-4

von Virag, A., Guichard, M., Neuditschko, M., Dietemann, V., & Dainat, B. (2022). Decreased Mite Reproduction to Select Varroa destructor (Acari: Varroidae) Resistant Honey Bees (Hymenoptera: Apidae): Limitations and Potential Methodological Improvements. Journal of Economic Entomology, 115(3), 695–705. https://doi.org/10.1093/jee/toac022