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.