The cause of a virus that wiped out billions of honeybees remains a mystery after new research disproved the theory that it was transmitted by mites.

For years scientists believed that the deformed wing virus (DWV) was spread by varroa destructor mites, which have invaded and spread infections among honeybee colonies in Britain.

But researchers from the Rothamsted research institute in Harpenden, Hertfordshire, found out that DWV does not grow within the mite. Instead, the infection has been found only inside the gut of the varroa, suggesting that the mite has merely eaten it from the bodies of bees already infected. Varroa mites cannot regurgitate their gut contents, and so would not be able to transmit the virus. The researchers used an antibody technique to track the viral particles. It does not appear that the virus has invaded the mites’ cells and can reproduce within them.

Teresa Santillan-Galicia, who led the study, which is published today, said: “The presence of deformed wing virus in large amounts in mite faeces suggests it is picked up during feeding on an infected bee. However, one important question remains: how is the virus transmitted to bees?

“It is likely that the amount of virus acquired by the mite plays an important role in the interaction between deformed wing virus and the varroa mite.

“Full understanding of the interaction between deformed wing virus and the varroa mite will provide basic information for the future development of more sustainable control strategies against the mite and the virus.”

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