Mites, not a virus, are the main threat to bees, study finds

Jan. 30 (UPI) -- Several studies have suggested parasitic mites both spread and worsen the effects of Deformed Wing Virus among honey bees. But new research shows the link between the two threats is tenuous.

In a new study published in the Proceedings of the Royal Society B: Biological Sciences, scientists in Australia argue mites pose the greater threat to honey bee health. The virus, they say, is mostly an innocent bystander.

"The prevailing wisdom is that the mite selects for very virulent strains of the virus," Madeleine Beekman, professor of environmental sciences at the University of Sydney, said in a news release. "For that reason, the virus is now known as a very dangerous virus and the Australian beekeepers are adamant this virus should not get into the country. In fact, there is legislation that prevents the import of any bee products that could contain the virus."

To better understand the relationship between the Varroa mite, a tissue-eating parasite, and deformed wing virus, scientists injected bee pupae with large amounts of the viral strain carried by mites.

Researchers have previously hypothesized that mites transmit a stronger version of the virus. But the latest lab tests showed the mite actually does the opposite. The strain transmitted by mites surpasses deadlier viruses, including the Sacbrood Virus and Black Queen Cell Virus.

With deadlier viruses eliminated in mite-infected bees, only the Deformed Wing Virus remains. The research showed Deformed Wing Virus alone doesn't kill bees.

"Our work therefore changes our understanding of the effect Varroa has on Deformed Wing Virus and the health of honey bee colonies," Beekman said. "It means we don't have to be scared of the virus. Instead we need to focus on eliminating the mite and reducing its numbers."

Australia is currently the only place in the world where honey bees remain mite-free. As a result, the country's honey is free of the traces of chemicals used to combat mite infections. However, most scientists believe it's only a matter of time before mites make their way Down Under. Beekeepers, researchers argue, need to start preparing for that inevitability.

"Many countries actively select for honey bee populations that can tolerate the Varroa mite without treatment. Australian beekeepers would like to import the sperm from such populations to start preparing their honey bees for when the mite arrives," Beekman said. "But the importation of the sperm is currently forbidden because of the threat of Deformed Wing Virus, which can be present in bee sperm. Perhaps beekeepers can now convince the authorities that bee sperm is safe."

The takeaway from the new study, according to Beekman and her colleagues, is that both beekeepers and researchers need to focus their efforts on combating the Varroa mite, not Deformed Wing Virus.