Last year, the parasitic mite Tropilaelaps mercedesae was detected in Europe for the first time. Immediately, the discussions about a new threat for honey bees came up. Another mite, another challenge for the beekeeping industry? The discussion took off when it was also found in Georgia (the European state, not the place in the USA). Rumours came up that it was also in Greece and other European countries. Without a proof of it.
So, besides the rumours, let’s look at the facts. Which, in my opinion, is the only way to prepare to and deal with new threats. Panicking and misinformation doesn’t help anyone.
What are Tropilaelaps mites?
Tropilaelaps mites live on honey bees and have a similar biology to varroa. Samesame, but different, as I often heard in Thailand (not only related to mites and bees). They reproduce in the capped brood and feed on the larvae and pupae. The big difference, apparently, is the dispersal phase, so the time they spend on adult bees: Only after one to two days after hatching, they enter the next brood cell. This shorter reproductive cycle increases the number of mites in the colonies faster than we know it from varroa mites. They also move very fast. I remember that it was difficult to observe and follow them, when they came out of an infested brood cell.
How they look like and where they come from
Tropilaelaps mites are smaller than varroa and have an elongated, brown body. Flip a varroa mite by 90° and cut it in thirds – then you have more or less the dimensions of it. When they come out of a brood cell, you also may see young mites that are still white. But being so small, they’re more difficult to see than varroa mites.
The original host of these mites are giant honey bees, Apis dorsata and Apis laboriosa. In Asia, they were also found on Apis cerana (the original host of varroa mites) and Apis florea (red dwarf honey bees). So, they already had switched to other hosts in their native distribution range. We know four species of these mites. Two of them, Tropilaelaps clarae and Tropilaelaps mercedesae, also use our honey bees as a host. The one spreading at the moment is the latter. In the following, I’ll be talking only about “Tropilaelaps” to make things a bit easier.
A new threat to honey bees?
When I was in Thailand in 1998/99, beekeepers who worked with Western honey bees told me that varroa wasn’t a problem. But Tropilaelaps was. Actually, the sentence “Mai mii varroa, mii Tropilaelaps” (There’s no varroa, there’s Tropilaelaps) is one of the few things I remember in Thai. One of the beekeepers got angry when he heard that I was working with varroa – and not the issue they were fighting with.
I understand that. And the “hype” now as a “new” threat reminded me of that, too. Tropilaelaps was an issue for many years already, but in the Western world we felt safe. Now that it’s coming near, it becomes a “new threat to honey bees”. It’s not new, it’s just new to some of us.
However, it’s not totally true that it was totally neglected before. Already in the beginnings of the varroa spread, there was a fear that also Tropilaelaps could make its way to other parts of the world. Which wasn’t the case for a long time. I.e., there’s also research from that time which can be built on.
Damages by Tropilaelaps
So, it may not be new, but is it a threat? In this case, I’m afraid, the answer is yes. The damages are, again, similar to those of varroa. The brood mortality is quite high and they also transmit viruses, like DWV or also Black Queen Cell Virus. In the end, the single bees have a shorter lifespan, the colonies get weaker, and collapse. Climate change is apparently favouring its spread, which makes it to one of the challenges that we have to prepare for.
Especially, as we obviously still don’t know everything. In the past the dominant opinion stated that Tropilaelaps doesn’t survive longer brood breaks. That’s also why beekeepers in temperate regions could feel quite safe. But apparently this isn’t absolutely true. There are regions with longer brood-free winters that still have issues with this parasite. If one of my readers is Korean, can you say something about this in the comments, please? In any case, a lot of brood makes colonies more susceptible to this mite.
Can we do something about Tropilaelaps?
As I said, we’re not “new” to this mite. It’s studied since the 1980s. Asian beekeepers treat it almost continuously with fluvalinate or amitraz strips. I saw that already when I was working in Thailand: Every Apis mellifera colony you opened, had strips of some sort. Apparently, that’s still the case, as I read in an article by Maggie Gill in a German beekeeping magazine. That’s an issue, as it favours resistance to these substances.
But organic acids seem to help, which have a much lower risk of resistance. In addition, brood breaks still could help. So, things like queen caging and a treatment with oxalic acid could be an option. This has to be studied yet, we don’t have data on that. But formic acid has been studied. With its action into brood cells it could be a very good option for Tropilaelaps which doesn’t stay that much time outside the brood cell.
Unfortunately, formic acid evaporates very quickly with warmer temperatures. In these conditions, the damage to the colonies (queen loss and dead brood) can be quite high. That’s the reason why formic acid is used mostly in cooler regions. That’s why I brought up the queen caging and oxalic acid treatment, which is independent of temperature. But again, it has to be studied first.
It would definitely help, though, if beekeepers wouldn’t import bees. This won’t stop the spread. But it would slow it down, giving scientists and consultants more time to develop strategies against Tropilaelaps. Or any other invasive species that could be a honey bee disease.
Stay calm and vigilant
So, though Tropilaelaps isn’t new threat for honey bees, it’s definitely a potential menace. As such, it has to be treated with calm and brains. The current discussion is way too sensationalist in many cases. That may help to get attention, but it doesn’t help to find solutions. For that, we need sober discussions, properly analysing the situation and the data we’re getting from the research. This needs time, going step by step. Sustainable solutions will have to be adapted over time, too. Because conditions change. Especially in times of global warming and biodiversity loss.
Beekeepers should now keep calm and vigilant. The project BeeGuards published a leaflet with information on Tropilaelaps, which will also show you how to identify this mite. There’s also a platform that collects all available information on this parasite, with maps and all relevant scientific papers. A useful resource for those who want to dig a bit deeper.
Most importantly, if you see something suspicious, don’t hesitate to inform the authorities in your country. Controlling a parasite or disease always means to know where it is. This parasitic mite may give us the chance to establish this aspect of good practices. Because be it varroa or Tropilaelaps: Bee health issues are solved only if everyone does their part.
