After the great bee death in the early 2000s, the honey bee population in Germany has slowly but surely increased again. In 2007 there were only 670,000 bee colonies in Germany, today there are nearly a million more.
But now scientists are warning of a new threat: a type of deadly deformed wing virus (DWV). According to the results of their study recently published in the journal International Journal of Parasitology: Parasitology and Wildlife The mutant pathogen appears to be spreading rapidly throughout the world. “The new DWV-B mutant is more lethal and possibly easier to transmit than the original pathogen,” says Robert Paxton, a zoologist at Martin Luther University Halle-Wittenberg. Infected animals usually die after 10 to 14 days.
It is not entirely clear how the virus kills bees. In any case, the deformed wings typical of the disease are not the main problem. Anyway, they only occur in already infected animals as pupae and then hatch with defective wings due to infection. But even adult bees, which you cannot distinguish from the outside, can become infected with pathogens and die from them. “Sick animals move much less and can’t function in the cell either,” Paxton says.
The virus takes two to three years to eradicate the entire population. “Most infected colonies die in the winter,” Paxton says. There is still no medicine against the virus itself. But against its carrier, the Varroa mite. The parasites, which are about one millimeter long and one and a half millimeters wide, suck blood, specifically hemolymph, from bees and transmit the deformed wing virus in the process. “It’s a bit like mosquitoes and the pathogens that cause malaria,” Paxton says. Vampires themselves are annoying, but they are not fatal. What’s really dangerous are the pathogens they transmit.
The new virus variant is now present in almost all large blocks
According to the study authors, there is evidence that the new DWV-B mutation, unlike the original virus, is not only transmitted by the Varroa mite, but also reproduces in the parasite. The scientists suspect in their study, “This could represent an additional mechanism that increases the incidence of DWV-B compared to DWV-A.”
Type B deforming wing virus was first discovered in 2001 in the Netherlands. 16 percent of their genome has been altered compared to the A variant. These changes seem to give the virus enormous benefits. This is the only way to explain why the aggressive DWV-B variant spreads so quickly and suppresses the original virus.
To find out the prevalence of the new variant, Paxton and his team evaluated genetic data and publications about DWV viruses found in honeybees around the world between 2008 and 2021. In addition, researchers in Germany, Great Britain and Italy sampled themselves. The result was: “The new virus variant is now present in all major land masses on Earth except Australia.” In the 2000s, DWV-B spread mainly in Europe and Africa. It has also been prevalent in North and South America since 2010 and can be detected in Asia since 2015. “In Germany there is now only type B,” says Paxton. You have completely replaced variable A.
Wild bees become infected from flowers previously visited by infected honeybees
What does this mean for beekeepers in Germany? “They have to pay more attention to hygiene in the hive than before to prevent Varroa mite infestation,” Paxton says. Because varroa mites infected with deformed wing virus transmit the pathogen to bees with a probability of close to one hundred percent. If the colony is already infested with mites, it should be treated with special insecticides that kill the mites, not the bees – twice a year if necessary.
In this way, beekeepers protect not only their bee colonies, but also wild bees, of which there are about 580 different species in Germany. Wild bees are at least as important pollinators as honeybees, and unlike them, many species are actually endangered. Some species, such as the common bumblebee, are known to be capable of contracting deformed wing virus. Laboratory studies have shown that infected bees also die earlier than healthy people.
“Wild bees become infected when they visit flowers in which a previously infected honey bee has collected and left its droppings,” Paxton says. So if the infection rate of the new virus in honeybee colonies can be kept low, the risk of infecting wild bees also decreases. Fortunately, transmission of Varroa mites from honeybees to their wild relatives is rare or impossible, as these parasites primarily affect honeybees.
But wild bees are more threatened by many other dangers than honeybees, which humans take care of in emergency situations. Intensive farming is one of the main reasons for the sharp decline in many wild bee species. On the other hand due to the abundance of pesticides and herbicides, the effects of which are not limited to the organisms that farmers want to control. Recently, an investigation into the journal Science Sciences He showed that glyphosate also harms bumblebees in a roundabout way. Perhaps the biggest problem for wild bees is habitat loss. The densely cultivated fields are like a green desert for insects, where they simply cannot find anything to eat.