The Scientist and the Beekeeper: The Tale of Varroa-resistance in Norway

Dr. Melissa Oddie

Part One

I remember first reading about Varroa destructor. It was portrayed as this apocalyptic plague that had descended on the world’s honey bees, spreading disease, and killing colonies at such a rate that beekeepers were throwing up their hands, walking away from a life-long passion because they could not take the crushing pressure. I read this, but I also read about the people fighting to control it: novel treatments, using mite predators, new management techniques, but the method that struck me the most was naturally-adapted mite resistance; using evolution to fight a problem that evolution had helped create.

My first trip to Norway was in 2015, about five months into my PhD. The work was on varroa resistance in European honeybees: resistance, in my mind, is the ability of honeybees to adapt and employ techniques to reduce mite population growth, rather than tolerate high loads. This method struck me because, like graduates of any Ecology and Evolution program, I had learned about the Red Queen Hypothesis: the arms race of adaption between two competing species. It seemed a self-adjusting strategy, to have bees adapt and manage the parasite. They would achieve a sort of dynamic equilibrium with it, living in a balanced push and pull for as long as nature saw fit. This would effectively prevent the catastrophic losses so many beekeepers were now fighting.

The roads were pitch black as I drove my rental, with no lights save my own, and the black silhouettes of the towering spruce crowding on both sides against a deep navy sky. It was about 10 pm one night in August and I was hopelessly lost; both geographically and apiculturally. Everything I had learned about bees up until that point, I had crammed in about four months, reading scientific papers and beekeeping blog - as many as I could.

Prior to this, I knew no more than any non-bee-associated person would. So, when I was sent to investigate Terje Reinertsen’s alleged “varroa-surviving” Buckfast bees, I held a healthy level of skepticism in the claim. The literature said that European honeybees died of varroa, and that was that. I almost did not find the house. Terje and his wife, Anita, had graciously said that I could stay in their spare room while I ran my observations. As luck would have it, I stopped to ask for directions at the very house I was supposed to find! Anita opened the door, invited me inside, and so begins the story.

Terje Reinertsen is a very typical beekeeper outwardly, with greying hair, a snowy white beard, a back bent from work and the kindest smile you would ever see, but I only needed to speak with him on a few occasions to know that his powers of observation were extraordinary. Terje noticed things about the bees most others would not. Each morning we would rise at the same time, while his wife still slept, and we would share breakfast and a conversation. Then, he would start his bee work and I would drive to my host institution to prepare my experiments. The words we exchanged at that kitchen table revolutionized my understanding of honey bees, because prior to that, they had been resigned to concepts of ink on paper, beyond the occasional forager that floated distantly past my office window. I did not know them, but Terje did.

Top: Terje and Melissa sit at the famous kitchen table discussing the results from the year 2021. Above: The experimental apiary used during the scientific studies from 2020-2022, set up by Terje and Melissa.

Mornings became routine: Terje would share his theories on the bees, what they were doing and why, and I absorbed everything, cross-referencing it with the textbook learning I had memorized before my trip. It gave me an appreciation for both perspectives, academic and experimental, and taught me the value of each: beekeepers observe, and they often do it well, so they catch things not yet described or explained by research, and research gives a crucial context to many of the beekeepers’ observations.

A capped brood frame in one of Terje's surviving colonies. Central in the photograph is a cell with an open cap to reveal the little hole made by the bees that has been capped back over with wax.

On days when there were no research tasks, I opted to shadow Terje as he worked with his bees, watching, learning, and working firsthand. I quickly became aware that Terje had such a keen understanding of them that, even though it was difficult to communicate, he could be relied upon to an astounding accuracy: bees were all about balance. If something was off, they reacted, adjusting their behaviour to return the colony to their version of normal. They were absorbing information I could only guess at, but Terje seemed to know what each response meant and what had caused it: the brood pattern was off, or they were not building drones where they should. Everything at every time in the season had a different reason and I slowly realized that forty years was a rather tight time limit to learn what Terje seemed to know.

The first measurements I took, counting varroa on the bottom boards of the colonies told a very interestng story; indeed, it seemed that a good number of Terje’s colonies had a much lower drop rate than expected, consistently over several measurements, and this was in autumn, when varroa would notoriously take over. So, there was some evidence for the “surviving” claim, but I still wasn’t convinced. The next bit of evidence came in the brood - because I suspected the lack of mites would continue there, I did not use brood frames in which eggs had been laid and capped by Terje’s own bees, but frames from other colonies that had a measurable issue with the mites. Each of ten colonies were given two capped frames, one of which was set into one of Terje’s colonies, and one into a local Carniolan colony with no reported resistance, and very clear mite evidence. Each of the five receiver colonies of both population types (Terje’s or Carniolan) got two frames from different donor colonies. The frames were removed after about nine days and since the brood used was laid in a specific time window, I knew most of the cell occupants would be about nine days old after capping, the perfect time to measure reproductive success in the mites. Terje’s bees did not disappoint. In that nine-day window they seemingly managed to influence the varroa reproductive rates, reducing the reproductive success on average by 30%, despite the mites coming from the same donor colonies in an apiary over fifty km away.

From left to right: Terje, Frank, Roar and Melissa crowd into the small grafting room in Terje's workshop.

Now, cell recapping is what I have published most on besides the ability of Terje’s bees to reduce the reproductive success of varroa. It is, simply put, a hygienic behaviour that exists in every colony, used to detect problems with and remove diseased brood. Where varroa is concerned, it seems highly associated with colonies that can reduce the population growth of the parasite. I did not discover this association in relation to varroa. I first read about it in one paper from the Baton Rouge lab in Louisiana: “Changes in Infestation, Cell Cap Condition, and Reproductive Status of Varroa destructor (Mesostigmata: Varroidae) in Brood Exposed to Honey Bees With Varroa Sensitive Hygiene” (1). It remarked that the bees opening a cell and capping back it over with wax was a by-product of complete brood removal in response to varroa invading and/or reproducing in brood cells. In the case of recapping, the brood is not removed, only the cell cap is opened, partly or completely, and then the hole is repaired, often by another bee. The brood remains undisturbed, to develop as it would normally. A simple recapping would not prevent the mite from reproducing, if it chose to remain in the cell, but it is possible that simply opening the cell may create enough of a disturbance to reduce the number of offspring a female is capable of rearing successfully, especially if the cell is opened more than once.

At this point, I had solid evidence that varroa numbers were lower and that their reproduction was being actively affected by something Terje’s bees were doing, but no method was yet apparent. I was tasked with measuring brood removal, or, VSH in my original experimental design that year, but to my chagrin, I found no difference between Terje’s bees and my controls in the number of brood cells missing from the test frames (which had been carefully photographed and mapped before and after the nine-day rearing period). Nor did they seem to be grooming themselves at any higher rate, at least, not in the month-long time window I was given (2).

I still believe it is possible that the bees could have been changing their varroa management tactics across a year, and I simply missed them, so VSH and grooming may play a role in survivability, and re-capping may just be a by-product after all, but back then, sitting in the tiny lab late one cool, August night, with three weeks gone and no evidence of any real mechanism for the difference in varroa I was measuring, I was at a loss. It was then I began to question everything I had been doing; there was something there, I had missed it and by then it was far too late to re-design and run any more experiments.

That was when I noticed it: a small discolouration in the cell cap on one of the frames given to Terje’s bees, and I thought back to that paper. Carefully, I excised the cap like one would open a can and turned it over - the cell had been opened before, but not by me, by the bees. Now that I had seen it once, I found it everywhere; in some colonies the rates were modest, in some, nearly every infested cell had been tampered with, but the key thing was it was only in the brood that had been given to Terje’s bees. The control frames were lucky to have two re-capped cells in 200. This was something, perhaps my life choices could be salvaged! At that point in the night, I heard a loud bang, and suddenly the hallway was flooded with water. One of the pipes in the automated coffee machine had burst, sending a solid jet squirting straight out from the break corner. I spent the next ten minutes splashing about, trying to find a wrench to shut the water off and then rescue my (now precious) brood samples from a soggy end.

I published a few times after that data. Terje’s colonies never disappointed me with their evidence of varroa survivability, no matter how many seasons of data I took. One notable publication in 2018 mentioned re-capping found in Norway and three other, scientifically-backed surviving honeybee populations in Europe (3). Since then, more researchers have begun to talk about re-capping, if not as an actual mechanism of varroa resistance, then at least an easily measurable proxy one can use to gauge a colony’s ability to survive. What happened concurrently in Norway was, in my mind, much more interesting. Terje and his ideas of breeding bees that did not require treatment was gaining traction, and my research served to support it. People were taking notice, they wanted to try it too and it was not long before national funding was granted to try and repeat Terje’s breeding efforts, but this time with a scientist heading and recording the process. They chose me.

To be continued in the next issue: May 2023.

References

(1) Harris J. W., Danka, R. G., & Villa, J. D. (2012). Changes in infestation, cell cap condition, and reproductive status of Varroa destructor (Mesostigmata: Varroidae) in brood exposed to honey bees with Varroa sensitive hygiene. Annals of the Entomological Society of America, 105(3), 512-518.

(2) Oddie M. A., Dahle, B., & Neumann, P. (2017). Norwegian honey bees surviving Varroa destructor mite infestations by means of natural selection. PeerJ, 5, e3956. (3) Oddie, M., Büchler, R., Dahle, B., Kovacic, M., Le Conte, Y., Locke, B., ... & Neumann, P. (2018). Rapid parallel evolu.on overcomes global honey bee parasite. Scien.fic reports, 8(1), 1-9.