Animals

Tiny Mite Killing Millions of Honeybees: Photos

We have fueled a perfect storm involving little mites and a virus that has been killing off millions of honeybees across the globe.

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The global pandemic that is killing bees worldwide is man-made, with humans fueling the spread of tiny disease-carrying mites, a new study finds. At the center of it all is the Varroa mite, which can harbor the virus for the bee-killing disease known as deformed wing virus, or DWV. The new study, published in the journal Science, found that European honeybees are the source of cases of DWV infecting hives worldwide. "Varroa mites feed on honeybee hemolymph or 'blood,'" lead author Lena Bayer-Wilfert, a senior lecturer in molecular evolution at the University of Exeter's Center for Ecology and Conservation, told Discovery News. "They can get infected or contaminated when they feed on infected honeybee larvae and can then in turn pass on the virus to new bee larvae."

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The mites have been inflicting a devastating double blow to bee colonies. They feed on bee larvae, a practice that itself is clearly damaging. Even worse, if the larvae were previously infected with DWV by another mite, the feasting parasite could then spread the virus to other larvae as well as to adult bees. For the study, Wilfert and her team sequenced data of DWV samples across the globe from both honeybees and the mites. They additionally tracked the occurrence of the mite worldwide. The researchers then used that information to reconstruct the spread of DWV. They found that the epidemic largely spread from Europe to North America, Australia and New Zealand. There was some two-way movement between Europe and Asia, but none between Asia and Australasia, despite their closer proximity. (Australasia refers to Australia, New Zealand, the island of New Guinea, and neighboring islands in the Pacific Ocean.) The scientists also looked at samples from other species suspected of transmitting the disease, including different species of honeybee, mite and bumblebees, but concluded that the European honeybee was the key transmitter.

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Look closely and you will see the mites attached to some of these honeybees. The researchers found that how the host bees and their mite parasites interact with each other has changed over the past century. Bayer-Wilfert explained that the change is due to a combination of increased man-made movement of bee colonies over large geographic scales, and the emergence of Varroa mites as a carrier of DWV, which humans facilitated. "Moving animals and plants around, especially to areas where they are not native, can facilitate the spread of diseases," she explained.

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The normal flight range of a bee hive's population is just over 6 miles, but because humans move whole hives over long distances, Varroa mites were able to spread from Southeast Asia through much of Russia within little more than a decade. "Some of the early spread can be traced back to efforts to increase beekeeping as part of developmental aid, largely a noble undertaking that did, however, contribute to the very rapid global spread of Varroa," Bayer-Wilfert said. She continued, "Honeybee queens, hives and bee products, such as pollen that can be used to supplement bees when local forage is poor, are also traded. In some cases, most notably pollen, we have only in recent years become aware of how easily these can spread diseases."

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DWV does not just infect honeybees. It can infect bumblebees and other pollinators too, according to the researchers. Future studies will look at the role mites may play in infecting wild and unmanaged pollinators, like bumblebees. The good news is that the virus does not sicken humans. Varroa mites also do not parasitize people.

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Symptoms of the virus include damaged wings and other bee body parts, miscoloring and paralysis of the legs and wings, and a severely reduced lifespan. Infected bees, such as this one, are typically expelled from the hive.

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Winter, with its cooler weather and reduced food sources for bees, is especially tough for DWV victims. Since the mites are so plentiful and the virus spreads easily, many bees within a hive can be infected at once. "That means that whole honeybee hives may be lost over the winter period," Bayer-Wilfert said. To combat the problem, she and her colleagues call for upholding existing restrictions of the international movement of honeybees. Efforts should also be made to ensure that areas that are free from Varroa mites remain that way. "This is particularly relevant for smaller islands that may not have been a priority so far," Bayer-Wilfert said. "The best way of achieving this is to make the local beekeeping community aware of the potential risks." She added that there are several chemical treatments to rid bees of mites, but the mites have started to develop resistance against them. A non-chemical way of combating the mites, she says, is to cultivate a comb of male drone bee larvae (male larvae are larger and a better food source for the mites). Then that comb can be removed -- along with the mites -- from the colony. "This means that some larvae have to be sacrificed, but there is not chemical exposure of the rest of the hive and the mites cannot develop resistance," she said.

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"Honeybees are our most important managed pollinator, but they face major threats across much of the globe," Mark Brown, a professor at Royal Holloway, University of London, told Discovery News. Brown is also the head of the university's Center for Ecology, Evolution and Behavior. "Understanding how deformed wing virus, which has a major impact on honeybee health, has spread around the world is important," he added. "It can help us to manage the future flow of honeybees and associated products to minimize the impact of emerging diseases like DWV, and to prevent the spread of future viruses." "Lena's results show clearly how DWV has spread, and thus give us clues as to where efforts could be best spent to protect the health of our managed honeybees, and the wild bees with which they interact."

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