Vespa velutina nigrithorax: the Asian hornet. Photo: Wikimedia Commons

 

by Guillaume Kaufmann

This is where we stood in 1983—a good beekeeping year when hives produced 10kg of honey! A threat was casting its shadow from the East, but beekeepers nurtured the secret hope of being spared. In 1985, panic! An apiary in Solothurn is infected. In 1987, 12'484 hives are decimated by varroa. In the press, one still reads signs of hope: “Varroasis, miracle cure?” speaking of an obscure, promising treatment based on natural stimuli, of which no one today retains the slightest memory. Protection zones and quarantines are established. Perhaps it is not too late? Without success. In 1988, Neuchâtel is the last canton affected: the game is over, varroa is everywhere.

I am telling you about a time I did not know, having been born that famous year 1988. And yet I imagine the shock! Those beekeepers who remember it likely had to go through all the stages of grief: grief for the beekeeping of their fathers and mothers. A simple beekeeping where one mainly feared the death’s-head hawkmoth and foulbrood, and where honey was simply given—like a gift of nature. Everything was about to change, and many would abandon their passion: too discouraging, too difficult to resist the scourge, and too hard to see one’s bees decimated. Others would face it and relearn almost everything, with the greatest resilience. Still others would lock themselves into denial: “I don’t have those creatures!” until they were shown them in drone brood.

My friends, if I tell you this story, it is because today we are facing the same challenge. For more than 15 years, the shadow has been looming from the West this time, from France. A batch of Chinese pottery contained a queen of a kind never seen in Europe: a black hornet with the appearance of a wasp. Arriving during a favourable spring, she would found—alone, despite all dangers—the first nest. The beginning of an inexorable colonisation that advanced at a speed of 60km/year to reach Spain, Portugal, and the entirety of France. The Asian hornet knocked at our door in 2017, in the Jura: an isolated queen, from which one hoped (always the same hope) that none would return. Another incursion occurred in Mont-sur-Rolle in 2019. It is an old Swiss habit to hope that our mountains will protect us: it will not come, it will not cross the Alps or the ridges, the altitude will kill it. And yet, it reappeared this year both in Le Noirmont at 1000m altitude and in Geneva, demonstrating its extraordinary capacity for acclimatisation.

Dear beekeepers, I want to be a little solemn today because it is imperative that everyone grasp what is happening. This advice is addressed to everyone because today we are all beginners! None of us has experience of what awaits us from next year onward. And we must start with a simple but very hard fact: no invasive species of hymenopteran (and there have been hundreds) has ever been eradicated. Take the time to reread this sentence and understand what it means. I know it will outrage some of you who will not want to believe it and will see it as a form of defeatism. Far from me the idea of giving up (I am, on the contrary, rolling up my sleeves), but it is a fact: the Asian hornet will invade our country no matter what we do. Together we will do everything in our power to slow it down so that we have time to prepare, but it is impossible to hope to push it back. Perhaps not next year, perhaps not the year after, but within 10 years nests will be counted in the thousands and enormous hive losses will be lamented if we do not grasp the scale of it. Some of you will be discouraged, others will face it. Almost everything will have to be relearned.

Identifying the threat

Source: apiservice.

Vespa velutina nigrithorax—this is the scientific name of the Asian hornet. Vespa velutina must not be confused with its European cousin, Vespa crabro, which lives in good harmony with our bees, even if it eats one from time to time. It is important that you can recognise it and distinguish these species. Our threat, the Asian hornet, has:

• A single yellow band on the abdomen, whereas the European hornet has several.
• Yellow tips on its legs.
• The ability to hover.
• Nests with a lateral entrance. They strongly resemble those of wasps and European hornets, but for the latter, the entrance is always at the base when nests are high up. All can also occur underground.

I ask you to study carefully the image showing the differences between the two hornets. Also go online to see Vespa velutina in flight. It is absolutely essential that you can recognise it! Our authorities, the SSA and apiservices, already have a strategy to fight the Asian hornet. But you have a central role in it and are the first link in the chain: it is from you that alerts are expected to trigger the procedure aimed at destroying nests. From next year onward, you will need to monitor your hive entrances—from August—to detect the presence of the intruder. You may also see it in orchards and near fruit or ivy. If you do not do this observation work, nothing will happen, and the Asian hornet will settle peacefully near your apiaries. Our fate is in our hands, and we must rise to the challenge.

Understanding the threat

Why is Vespa velutina particularly feared? Because unlike Asian bees such as Apis cerana (the same species that coexists with varroa), our Apis mellifera has not had millennia of cohabitation that would have allowed it to develop defence strategies. When the Asian hornet attacks our hives, our bees do not know what to do. The hornets hover above the landing boards and wait for foragers slowed by their load of honey or pollen to return to the hive. The hornet then grabs them, carries them a little further away, decapitates them, and keeps only the thorax, rich in protein, making small pellets used to feed its larvae. During a good day, a hornet will capture some 150 workers. It is estimated that a hornet nest, with around 3000 individuals, can, during the month of August alone, decimate more than 60'000 bees—two strong colonies. Up to the first frosts of October or November, this is therefore equivalent to 6 to 7 hives that will be lost.

Hornet stationed in front of a hive, waiting for a forager to return. Photo: MNHN (France)

Of course, these worker losses weaken colonies. But the main threat is not there. Unable to defend themselves, our bees retreat into the hives, block the entrances, and stop all activity. During the last months of the year, there is no longer any nectar intake (which can be compensated with syrup) but also no pollen intake. It is often this resource that is then lacking in spring, leading to major colony losses. The presence of the hornet also induces very high stress, which weakens colonies.

In the weakest hives—and where entrances are poorly adapted—the hornet can also enter and wreak havoc, even attacking brood. One can nevertheless fairly easily protect against this problem with entrances that only allow bees to pass. But such a hive does not need to be visited by the hornet to succumb in spring.

Multiplying the threat

Fortunately, this catastrophic scenario occurs only at the end of the season, leaving us a fairly precise window of time in which to intervene. It is important to understand the Asian hornet’s reproductive cycle to know what to expect.

As with wasps, hornet queens live only one year. With the first frosts, workers and males die and the nest is abandoned. Several hundred fertilised individuals—foundresses—then leave the nest and hide wherever they can to spend the winter: under bark, in a hole left by a rodent, in a Chinese pot. At the first light of spring, they emerge, refuel their energy, and set out alone to build a first rudimentary nest. It is quite impressive to imagine that these foundresses, before becoming queens of a kingdom, must build it entirely and without help. The foundress will create the first cells in which she will raise her first workers. These will be underdeveloped and very small, but the queen will have her first few dozen workers, who will take over the expansion of the nest and the search for food. These small workers will not trouble our bees too much, which can still compete. During June, the queen no longer leaves the primary nest, where she will only lay eggs. This quickly becomes too small for the ever-growing colony. It is time to migrate: the queen and a good part of the workers will then set out to build a secondary nest, often very high in trees. The primary nest will still be occupied until the last nymphs emerge.

Source: MNHN (France) Photos: JH = J. Haxaire, MD = M. Duret, QR = Q. Rome, CV = C. Villemant.

It is in the secondary nest, much larger and built rapidly, that the large mature workers will emerge. The time then comes for expansion; the queen lays the first males, and protein is needed to raise all of them. This is when our hives will be attacked. Among the workers, some will develop sexual organs and be fertilised by the males. These new foundresses (indistinguishable from workers by observation) are estimated at around 500, but their number could be far higher in exceptional years.

With the first frosts, these 500 foundresses then seek shelter so that the cycle can begin again. The old queen, the workers, and the males will die from the cold, and their nest will be abandoned. 500 may seem like a huge number, but it appears that only a few foundresses manage to establish nests the following spring. Cold, birds, other insects, rodents, etc. will kill the vast majority (more than 98%). But the few that succeed will be enough for the threat to spread again and again.

Fighting the threat

A heroic climber lost in the branches of the Côtes du Doubs. The nest was perched at 38m! Photo: Lukas Seehausen, CABI.

The safest and most effective strategy to fight the Asian hornet therefore lies in destroying nests. It is essential that nests and their inhabitants be destroyed before the migration of foundresses at the end of autumn. When this is achieved, one ensures that the nest will leave no offspring. The only problem: locating nests can be very difficult. Several experts admit that even when they could determine that a nest was in a specific tree, it was sometimes impossible to see it from the ground, as the leaves concealed it. And this even for enormous nests approaching 1m in diameter.

Several techniques are being tested. The three nests destroyed this year in Geneva and in the Jura were located thanks to beacons emitting a radio signal and attached to captured hornet workers. This technique is promising and will probably be prioritised here at the beginning of the invasion. Other research groups are trying to use thermal cameras to locate colonies in trees, but leaves and the excellent insulation of nests make the task difficult. Italians are trying to deploy harmonic radars that can detect small metal residues placed on captured workers. Here again, the technique seems promising, but it is very costly. The last known technique consists in estimating the position of a nest based on the flight paths of workers. With several observation points and triangulation, it seems possible to succeed. But even after narrowing down a reasonable area, the nest remains a needle in a haystack.

In all cases, the starting point is always the observation of hornet workers, often near apiaries. To be effective in locating nests, it is also essential that all apiaries are properly declared to cantonal inspectors and that their position can be communicated quickly. If an apiary is attacked, it is important to visit other apiaries within a 2km radius: this can already greatly guide the search. Undeclared apiaries are a scourge in the event of epizootics and also risk being so in the event of hornet attacks.

The nest barely visible in the canopy. Drone photo by Nicolas Chevre.

Locating nests is not the only difficult step: destruction also brings its share of challenges. The Jura nest was located 38m above the ground in a forest on a steep slope of the Côtes du Doubs—meaning that no aerial platform could be brought in. Fortunately, it was possible to rely on two heroic climbers (one to treat the nest, the other to retrieve it). But it is to be expected that each nest will bring its own surprises. In any case, it is absolutely not expected that you deal with a nest yourselves. Your task is to spot the presence of the Asian hornet in your apiaries and to contact apiservice by email (info@apiservice.ch) or by post (apiservice, Schwarzenburgstrasse 161, 3003 Bern). It is important that you have a photo, or even a captured specimen so that it is possible to ensure that it is indeed Vespa velutina. Do not forget to indicate the date and the place where the specimen originates. Authorities receive hundreds of photos of flies, wasps, or even bees from the public who think they have discovered Asian hornets. If you are relied upon in particular, it is because you are likely to encounter hornets during your beekeeping activities, and because you are recognised as having skills that should allow you to identify an insect. But once again, train yourselves!

Hornet worker captured in Le Noirmont with a transmitter attached. Photo: Lukas Seehausen, CABI.

The problem with photos

Let us be frank: the requirement that a photo be taken is a weakness in our control plan. It is not always easy for everyone to take sharp photos of an immobile landscape. Now imagine a fast insect in full flight … Even for seasoned photographers, it is a challenge! What I advise, if you cannot take decent photos of what you suspect to be an Asian hornet, is to take a video. This is often much easier, and it is then possible to create screenshots. Free software such as VLC makes this very easy (several photos accompanying my advice come from this technique). Here again, do not hesitate to practise and ask for help if you cannot manage. This also assumes that you always have a camera (or a smartphone) with you at the apiary, in any case at the end of the season. Of course, if you manage to capture and kill a hornet, it will also be easier.

The trap controversy

Once one understands that nests are built by a handful of foundresses that barely made it through winter, the idea naturally arises to try to eliminate them by trapping. The internet is full of videos showing beekeepers checking their traps and proposing more or less sophisticated trap designs. Scientists are unanimous about the ineffectiveness of this approach as well as its danger to biodiversity. Without a truly selective solution, these trapping campaigns mainly result in slaughter of other insects. It often takes hundreds of dead insects to catch a few Asian hornets. Moreover, an Asian hornet killed in spring does not necessarily mean one fewer nest. Indeed, more than 98% of foundresses will not manage to build a mature nest. Such campaigns can at best raise the proportion by a few tenths. Most of the trapped foundresses are those that would, in any case, have been eaten by a bird or another predator. We are facing what mathematicians call an asymptotic phenomenon: the closer one gets to 100%, the more colossal the efforts required, and the more sacrifices are demanded from biodiversity. Yet one never reaches 100%. Our fight against varroa has taught us: even with 98% efficacy of oxalic acid treatments, there are thousands of varroa in our hives the following autumn. Even if, by multiplying treatments and stressing our bees further, we reached 99.5%, it would not fundamentally change the situation.

Another reason not to trap foundresses in spring: they engage in a form of competition and can fight and steal nests from one another. This competition phenomenon eliminates a large share of candidates to establish a mature nest. The more foundresses are trapped, the less this natural thinning occurs. Thus, the already low effectiveness of trapping is unfortunately offset by the reduction of natural competition among foundresses. Three French departments are currently participating in a study on the real effectiveness of spring trapping. For now, however, nothing indicates that it is effective, and everything shows that it is dangerous for biodiversity.

There remains the question of traps near apiaries when hornets attack in autumn. Here again, the internet is full of models promising the moon, as well as testimonies from people who tried and show that things are not so simple. Here again, we must wait for solid studies and trials, which will take some time to arrive. Until then, do your best.

For now, the most effective solution is as follows: protect hive entrances with 6mm mesh so that hornets are kept about twenty centimetres away. Bees are then less stressed and do not stop flying. Many foragers die, but colonies have up to 50% higher chances of making it through winter. Details and construction plans for such hive muzzles are available on abeille.ch, quick reference guide 2.7.1. Why not start building them this winter? You will need them sooner or later.

Concretely, what should be done?

• Plan for meshes in front of hive entrances for the end of the season. It is never too late to equip yourselves with this type of material.
• Take good care of your colonies: keep only strong, vigorous, and populous hives at the end of summer. Do not hesitate to unite—and even eliminate—those that limped through the season.
• Spend time observing your hives from August onward. Come by regularly and keep an eye out. If you see Asian hornets, photograph them or capture them, then contact apiservice by email (info@apiservice.ch) or by post A (apiservice, Schwarzenburgstrasse 161, 3003 Bern).
• In any case, prepare yourselves—and do so starting today! We have learned to live with varroa; we will learn to live with the Asian hornet. That said, the sooner we accept the scale and seriousness of the threat, the more coordinated our action can be, and the better we will be able to face it. Good luck to you, beekeeping friends. We will take stock next autumn!

 

See also:

• Vespa velutina, Asian hornet
• Apiservice quick reference guide
• Threats to our bees