Varroa Resistance: It Comes from the Queen

For those involved in bee improvement and breeding, a key question has always been:

Do bees learn Varroa-resistant behaviour from each other, or is it inherited?

by the Scientific & Technical Working Group: Karl Colyer and Paul Verrier

A review of Martin et al. (2024), Apidologie “Resistance to Varroa destructor is mainly transmitted by the queen and not via worker learning”

How the study worked
The team carried out queen swap experiments in both Hawaii and England:

• Varroa resistant colonies were given mite-susceptible queens
• Mite-susceptible colonies were given Varroa resistant queens

They then tracked mite levels and behaviour over time.

What they found

1. Mite-susceptible queens led to colony failure

• Mite levels rose significantly
• Colonies eventually died

This happened even when the original workers had been from resistant stock. Resistant workers did not pass on their behaviour.

2. Varroa resistant queens produced resistant colonies

• Mite levels stayed low
• Colonies survived and reproduced

This occurred even when starting with susceptible workers. The queen’s offspring determined the outcome.

3. Hygienic behaviour follows the queen
Key traits such as detecting infested brood, uncapping/recapping cells and removing infested pupae were strong only in colonies headed by Varroa resistant queens.

Some mite-susceptible colonies showed partial responses (e.g. recapping), but failed to control mites effectively.

Implications for BIBBA breeding work

Queen selection is central
This paper reinforces a core BIBBA principle that Improvement depends on selecting and propagating the right queens. Worker origin matters far less than the genetics of the queen.

Requeening is an effective tool
To improve a colony, introduce a queen from resistant stock and allow her offspring to replace the existing bees. There is no need to transfer across the worker bees from resistant colonies.

Local breeding works
The study used locally mated queens, and resistance was maintained. This supports open-mating and, possibly, the importance of improving the local drone population

A practical BIBBA takeaway
For BIBBA members, the message is straightforward:

• Identify and breed from proven resistant colonies
• Use requeening to spread those traits
• Work collectively to improve local mating conditions

Conclusion
This study provides strong scientific backing for what many breeders have observed in practice; If you want Varroa-resistant bees, breed from the right queens. This places BIBBA’s long-standing focus on selection, breeding, and local improvement firmly on the right track

Feedback from the Scientific & Technical Team

• Although limited to two sites and a relatively small number of colonies, the clear take home message is that colonies headed by varroa naïve queens lose VR activity with a corresponding increase in the levels of varroa. Intriguingly, these colonies also suffered high losses over the course of the experiment – a development that could be consistent with exposure to increased viral pathogen loads.
  
  
• It’s worth noting that several varroa naïve queens swarmed during the course of the study with their colonies being taken over by a daughter which presumably mated with local, presumably VR, drones. Despite this input of paternal VR genetics, these colonies still appeared to be varroa sensitive – although the numbers were extremely small.
  
  
• Overall, this study shows that VR traits are genetically encoded and possibly maternally inherited. Suggesting that a locally mated VR queen used to re-queen any colony will ultimately cause this colony to itself become VR.
  
  
• Given the scale of commercial queen rearing, this suggests that VR traits, once taken up by commercial queen producers, could be rapidly disseminated. And may even represent an ‘added value’ trait to those queen rearers ready to make the leap…

• The inheritance of VR gene(s) seems likely, but it would be interesting to see what happens on the next generation(s) of presumably, open- mated queens. It would be useful to see how well the trait persists.

• It always seemed reasonable to me that the VR trait of brood uncapping might be genetic because (as the authors spotted), the Grindrod and Martin 2021 paper identified that there are two unique compounds (ketones and acetates are stated) that are present when there are varroa mite offspring present in the cell. This one could presume lead to the suspicion that the VR bees have developed the ability to recognise this new off-smell and consider it requires investigation. It is possible that the compounds found are often below the sensitivity of the workers sensilla and there may not be sufficient sensing for low levels. This is then open to an evolutionary mutation that leads to greater sensilla sensitivity to the particular compounds, or just another sensilla pack maybe. This may then lead to; once a VR queen, we have a chance of always a VR queen if the gene is not too recessive. The gene or genes responsible may of course not be the direct cause of a change, but maybe it initiates some other possible epigenetic change that gives rise to additional sensilla or modified sensilla production – the mechanism may be extremely complex.
  
  
• For the BIBBA member this paper bears really good news. Once you have a VR queen you could easily get more and repopulate your apiary with potentially VR queens.
  
  
• In the small apiary, there is the opportunity of just getting some VR queens from local breeders of local bees.
  
  
• There really is some long-term hope that this might at long last be a good solid reason to celebrate that our bees can live with varroa and see it off when it matters.