Facing Tropilaelaps: learning from the field, not assumptions by Dr. Maggie Gill

Introduction

Most us here in Nairnshire are waiting for warmer weather before we do our first colony inspections. Strong winds this week make 10°C feel even chillier, and heavy showers curtail foraging.  But we can still plan ahead, get all the extra equipment ready for swarm season and make bivouac lures.

I read a recent scientific paper suggesting that swarming will probably enhance the spread of tropilaelaps when it arrives here in the UK. Not what I imagined at all given that swarming can actually help reduce varroa levels. So, it got me thinking—what else do we imagine about tropilaelaps, compared with varroa, in terms of how it will behave that might not be true? I asked Dr. Maggie Gill senior UK government scientist if she could share some of her cutting-edge work with us. Maggie’s remit with DEFRA (Department for Environment, Food, and Rural Affairs) is wide-ranging, and she is also an experienced beekeeper.  Our interests are central to her work in sustainable agriculture and pollinator health. Driven partly by inadequate government funding, Dr. Gill set up PHIRA Science to support pollinators and enable scientists to study diseases and pests like tropilaelaps first-hand in countries where it is currently endemic, but on the move — ever onwards towards us. 

Thank you very much, Maggie, for taking the time to put together this thought-provoking and important article for us when you were also preparing to head off to Georgia again.  I appreciate all the work that is being done on our behalf and I shall be donating again to PHIRA Science to help keep this crucial work going; https://www.phira-science.org/

Tropilaelaps

When Varroa first arrived in the UK, we were caught unprepared. There was little practical knowledge, limited research, and no real warning of what was to come. The result was devastating. Tropilaelaps will hopefully be different. This time, we have warning. We can see it moving west. We can watch what’s happening in places like Thailand and, more recently, Georgia. In theory, this should give us an advantage.

But I’m increasingly concerned that we may not be using that advantage as well as we could.

There is already a narrative forming. That Tropilaelaps will behave much like Varroa, that our existing treatments will largely work, and that bees showing resistance to Varroa may also cope better with this new parasite.

It’s a reassuring idea. The problem is that the evidence just doesn’t support the idea.

What I saw in Georgia

In 2025, I spent time in Georgia working with beekeepers who were dealing with Tropilaelaps for the first time, and I have kept in touch with these beekeepers over the winter and will return in a week or so to start the 2026 research. This has given me a rare opportunity to see a parasite at the point of arrival, rather than once it’s already become established.

What struck me most was the speed of Tropilaelaps. Colonies that started with very low levels of infestation built up to damaging levels within a matter of months. In one study, colonies deliberately infested with a small number of mites in spring reached levels that threatened their survival by mid-summer (in fact 20% of the colonies died). That’s not Varroa.

Alongside this, we saw how easily Tropilaelaps spreads. In the space of one season Tropilaelaps has spread from the northwest of Georgia, where it is thought to have arrived from Russia via the narrow corridor between the Greater Caucus mountains and the Black Sea, right the way across the country to the southern and eastern borders. Swarming, which many of us think of as a natural reset for Varroa, doesn’t reduce the problem, in fact, it seems to help the mites move. We found that mites could leave with swarms and successfully establish in new colonies. Even in relatively isolated apiaries, reinfestation happened.

That implications for the rest of Europe and the UK are hard to ignore.

The beekeeping nuns

One of the most memorable experiences has been working with Daniella and Natalie, two nuns managing an 86-colony apiary at a convent in western Georgia. They are thoughtful, observant beekeepers. Meticulous record keepers, not following trends blindly, but constantly questioning what they see. Their apiary is also closed: they don’t move bees, and they don’t collect swarms. If anyone had a chance of keeping Tropilaelaps out, it was them.

And yet, it still arrived.

At first, only two mites were found in March. But within a relatively short time (mid-June), every colony in the apiary was infested. What followed was an extraordinary level of effort: frequent inspections, brood interruption through queen caging, repeated treatments, and close monitoring. They managed to stabilise the situation, but only just, and only through an intensity of management that most beekeepers simply wouldn’t be able to sustain.

What stayed with me wasn’t just the science—it was the workload, and the uncertainty.

When bee behaviour doesn’t behave as expected

One of the more interesting, and slightly uncomfortable questions is how our bees themselves will respond to Tropilaelaps.

There’s been some suggestion that bees showing resistance to Varroa, particularly through hygienic behaviours like uncapping and removing brood, may also cope better with Tropilaelaps. It’s an attractive idea. But at the moment, it’s just an assumption.

Some preliminary observations I made in Georgia last October suggest the situation may be more complicated. Colonies that demonstrated brood uncapping and recapping behaviours consistently had higher levels of Tropilaelaps that colonies that didn’t exhibit this behaviour. I began to suspect that uncapping and recapping brood might actually increase Tropilaelaps levels in certain situations. The thinking is this: Tropilaelaps reproduce and mature quickly under sealed brood. If bees uncap those cells, they may release mature mites earlier than would otherwise happen. Those mites are then free to move on to new brood cells as Tropilaelaps do not need to feed on adult bees in order to be able to reproduce and here they simply being to reproduce again.

So instead of interrupting reproduction, the behaviour could potentially accelerate it.

That’s speculative at this stage, and I’ll be doing more work on it this year. But it highlights something important: we can’t assume that traits which help against Varroa will automatically help against Tropilaelaps.

A gap we can’t ignore

What’s becoming increasingly clear is how much we still don’t know.

• How will Tropilaelaps behave over multiple seasons in a UK climate? They have faired surprisingly well over the winter of 2025 and 2026 in Georgia, which is doing little to reassure this beekeeper.
• Which treatments will actually work, and how will control of Tropilaelaps differ from that of Varroa? Again, my observations from Georgia show that formic acid is an effective treatment. However, this is a harsh treatment for colonies to tolerate and multiple treatments are needed throughout a season to manage reinfestation and high levels of reproduction. The added workload that this entails will impact the financial viability of commercial beekeepers and for hobbyists could make what was once an enjoyable pastime a chore.
• How important are viruses in colony collapse? Tropilaelaps are a difficult mite to research. They are very small and difficult to handle and until recently were only present in Asia. While there has been some research into viral transmission through Tropilaelaps there has been nowhere near as much as similar work with Varroa. It’s clear from the work that Tropilaelaps vector viruses and this undoubtably contributes to colony collapse but to what extent is not fully understood.
• Will any form of natural resistance emerge quickly enough to matter? And are we being too narrow in what we select for? Beekeepers have spent decades trying to breed bees that can live with Varroa, and while progress has been made, it’s worth asking how robust that “resistance” really is. In many cases, when these bees are moved outside the environment they were selected in, the resistant traits become far less evident and after two or three generations, they can disappear altogether. If truly universal Varroa resistance existed, Varroa would no longer be the global problem it still clearly is. That raises an uncomfortable question: in focusing so heavily on selecting for Varroa resistance, what have we lost? Honey bee populations are the product of complex, locally adapted genetics. By narrowing that diversity, we may have inadvertently reduced traits that could prove important against other threats. Tropilaelaps may be one of those threats. The behaviours that help control Varroa, particularly hygienic behaviours like uncapping and recapping brood, are often assumed to be beneficial. But they may not function in the same way here. My observations from Georgia suggest they could even have the opposite effect, potentially accelerating Tropilaelaps reproduction by releasing mature mites earlier. By contrast, entirely different mechanisms, such as mite mutilation, may prove more important, but we simply don’t know yet. The key point is this: we cannot assume that because something works against Varroa, it will work against Tropilaelaps. They are very different parasites, and the bees’ responses to them may need to be different too.

These aren’t small questions—and right now, we don’t have solid answers to many of them.

What worries me is not just the uncertainty, but the risk of filling that uncertainty with assumptions.

Why PHIRA-Science exists

PHIRA-Science was set up because of this gap.

Quite simply, there isn’t the level of government-funded field research you might expect for something with the potential impact of Tropilaelaps. Laboratory work is happening, but practical, on-the-ground studies, watching how this mite behaves in real apiaries, are much more limited.

So, we decided to start doing that work ourselves.

It’s small-scale, and it’s operating on a very tight budget. But it’s focused on the questions that matter to beekeepers:

• How fast does Tropilaelaps spread in real conditions?
• What actually works for detection in an apiary?
• How effective are different treatment approaches in practice?
• What happens when you apply “standard” Varroa strategies?

We’ve started to address these questions through our work in Georgia, where the mite has only recently arrived. This gives us a chance to observe these early stages of infestation properly in a beekeeping system that much more closely resembles what we are familiar with in the UK and Western beekeeping.

Much of the existing research from Asia has been carried out in very different conditions—often with smaller colonies, different hive systems, and within tropical climates where brood is present almost year-round. Those differences matter. Colony size, seasonality, and management practices all influence how a parasite behaves. Georgia, by contrast, offers a far more comparable setting: larger colonies, temperate conditions, and beekeeping practices that are much closer to our own.

It’s not a perfect solution—but it’s a start.

Reasons not to give up

All of this might sound quite bleak. But there is something important to hold on to: we are not where we were with Varroa. We have time – some time, at least. We can learn from other regions. We can test ideas before the mite arrives here. We can question assumptions rather than relying on them. That doesn’t mean Tropilaelaps won’t be a serious challenge. It almost certainly will be. But it does mean we have a chance to respond differently.

What can we do now?

There’s no simple checklist, but there are a couple of things that feel increasingly important:

Learn how to look in brood
Tropilaelaps is easy to miss in colonies. Getting comfortable with brood inspection will matter because as Tropilaelaps spreads it’s the beekeepers that find it first. If we are to stand any chance of early detection and eradication every beekeeper needs to take on the responsibility of checking their colonies for Tropilaelaps.

Stay curious, not complacent
If something sounds reassuring but isn’t backed by evidence, it’s worth questioning. Some of what we “know” from Varroa may not apply. Being flexible, open to new ideas and staying informed will be important.

A final reflection

Tropilaelaps is on its way. The real difference this time is that we are not completely in the dark. But having a warning only helps if we take it seriously and if we assume too much, too early, we risk repeating the past.

If we stay open, observant, and willing to question what we think we know, we give ourselves, and our bees, a better chance.