Western honey bees are in danger: American and European beekeepers have been reporting massive bee losses for several years. One of the main causes of these losses is the varroa mite. In the past, efforts to control this parasite have concentrated exclusively on treatment in the hive, but foraging bees then bring back new mites when they return home. Bayer’s scientists have been working with bee researchers from Frankfurt University to develop the varroa gate, which is designed to prevent reinfection. This innovative front door should effectively protect the hive against the deadly parasite.
Life in the hive is highly organized, with busy insects working all around the queen. Worker bees distribute pollen, clean and look after larvae, or defend the entrance against enemy invaders like wasps and other honey thieves. But the varroa mite, Varroa destructor, slips in unnoticed on the bodies of some worker bees, evading the strict door policy. It brings a deadly danger with it; this tiny, brown arachnid can wipe out entire bee colonies. Like a tick, it fastens itself onto a bee with its jaws and so sneaks its way into the realm of the hard-working nectar collectors. Once inside, mites reproduce by laying their eggs in the honeycombs where new bees are raised. After ten to fourteen days their offspring spread throughout the bee population along with the newly emerged bees.
Varroa mites transmit dangerous viruses and bacteria
Varroa mites transmit pathogens like viruses and bacteria which are damaging to bee health. This parasite has wiped out entire populations of Western honey bees over recent years. Without human intervention, infestation with varroa means certain death sooner or later for honey bees in Europe and America. Things are different in Asia, where the deadly mite originated. There, a balanced relationship between the parasite and its original host, the Eastern honey bee or Apis cerana, has evolved over many generations.
The varroa mite was not seen in Europe until the 1970s and in America until the 1980s, but since its introduction it has caused massive bee deaths, as the Western honey bee has no defense against the parasite.
This was a disaster not just for beekeepers: in most countries honey bees are the main pollinator of crops such as apples, oilseed rape and almonds. In Europe, they are therefore regarded as the third most important domesticated animal after cattle and pigs.
”But this service provided by nature is under threat – and so is our food supply – if varroa is not adequately controlled,” comments Dr. Klemens Krieger, a parasitologist working in Bayer’s Animal Health Division.
However, for years the mite was not recognized as the main cause of large-scale bee death. Says Krieger, “Many scientists concentrated on viral infections or other factors such as pesticides or pollen from genetically modified crops, ignoring the harmful effects of the varroa mite.”
He followed a different path, reasoning that “Why focus on viruses, for instance, if they cannot do any damage without the mite that carries them?” A four-year field study by the Bee Research Institute in Oberursel, Germany has found that the parasite is at the heart of the problem: “If we keep up our efforts at controlling the varroa mite, many more bee populations will survive,” explains Professor Nikolaus Koeniger, who was the institute’s director for many years; he and his wife have been devoted to studying the varroa mite for decades.
As this famous bee expert couple knows, it is horizontal infection that is most dangerous. “Particularly at the end of the flowering period, foraging bees from healthy colonies invade colonies weakened by varroa to steal honey.
They then become infected and take back large numbers of mites to their own population.” The researchers want to prevent this transfer of mites, since “it is vital for effective mite control to stop new pests constantly entering the hive.”
They have therefore concentrated on the strategically most important point, and the joint efforts of the Bee Institute and Bayer have led to the creation of the varroa gate, a structure at the entrance to the hive. Every bee must climb through this gate when leaving or returning to its own hive. At first sight it doesn’t look anything special: just a plastic strip with holes through which the bees fly in and out.
Inspired by tick collars worn by dogs and cats
Only a closer look shows the immense benefits of this innovation. The plastic strip is coated in chemicals. Whenever a bee passes through the gate, it touches the edge. This transfers a mite poison (acaricide) to the bee and kills any mites it may be carrying. The substance needs to be permanently available on the surface of the strip so that protection can last for several weeks. This proved to be a particular technical challenge. It was solved when Bayer’s scientists thought back to an earlier project: the flea and tick collar Seresto™ for dogs and cats.
This innovative collar was the result of a joint venture by scientists from Bayer HealthCare’s Animal Health Division, Bayer MaterialScience and Bayer CropScience.
They used a little physical trick: “The active substance molecules move between the polymer chains of the plastic matrix. They are always trying to balance out the gap in concentrations between the collar and the animal’s coat, and so rise to the surface. When some of the active substance is removed, it is automatically replenished,” says Krieger, explaining the principle.
Scientists are now using the same system to protect bees: “The acaricide is embedded in the plastic. When some is transferred to the legs or hairs of a bee, fresh supplies are automatically released from the strip to balance out the gap in concentrations between the plastic matrix and the surface,” he explains. This means that the device remains fully effective for the several weeks needed for treatment. At the same time, the amount of chemical available is never more than necessary. Scientists are still fine-tuning the formulation and application rate, and are testing two Bayer substances on bee populations in the field at various concentrations.
The findings to date show that “the bees have been fully protected against reinfection, and no side effects have been seen,” says Gudrun Koeniger.
The bee experts have also been testing for residues in honey and wax.
According to Krieger, “the analysts have been working at the limits of their equipment and methods.” But the formulation is not the only important factor in really barring the way to mites.
Integrated control approach vital for real protection
Careful consideration must also be given to the shape of the gate: “What we are doing is building a barrier on the beehive, but it must not interfere with hive ventilation or traffic,” comments Nikolaus Koeniger. And yet it must release enough chemicals to control the mites. Scientists are conducting a battery of tests to find just the right delicate balance between shape, formulation and function, testing various hole sizes and distances, for example.
To ensure that Western honey bees can continue to do their vital pollination work in future, beekeepers will be able to install this innovative bee protection gate to protect their colonies against parasites in late summer, before the bees become dormant for the winter and stop flying. It is then that long-lived winter bees emerge, to ensure that the colony survives the winter. “We have learned over the past few decades that no single weapon is effective in controlling mites. We need an integrated approach to mite control,” comments Gudrun Koeniger. The bee gate should close an important gap in the integrated control concept.
Interview: “Effective control of varroa mites”
Mariano Higes is a bee researcher at the Bee Diseases Laboratory of the Spanish bee research institute, the Centro Apícola de Castilla-La Mancha.
Rresearch talked to him about bee health.
What other factors are responsible for bee death in addition to varroa?
It varies from region to region. For example, in Spain we have found that Varroa destructor is not the only problem. The single-cell parasite Nosema ceranae, which also originated in Asia, also plays an important part, as do the viruses spread by varroa and nosema.
Are crop protection products dangerous to bees?
The finger of blame is often pointed at insecticides, but our investigations show that they are not involved at all in bee losses in Spain. This does not mean that in some parts of the country uncontrolled use of these insecticides cannot cause bee losses, but they are not behind widespread bee death.
Will bee numbers recover?
Not without efficient control of the varroa mite by the targeted use of appropriate mite controls, that much is certain. We also need products to control Nosema ceranae.