A devastating virus that has infected bees worldwide spread through global trade in pollinators used in commercial farming, a study in the journal Science finds. “Deformed wing virus,” spread by the Varroa mite, leads to significant mortality in overwintering colonies of honeybees, which pollinate fruits, nuts and other crops.
The virus isn’t the only factor in the worrisome recent rise in bee deaths. Neonicotinoid pesticides, which are among the most widely used pesticides, have been implicated, too. Bees encounter the pesticides by visiting plant species sprayed with the chemicals. Deformed wing virus strikes in the winter, among mite-infested colonies, and is one of the most deadly diseases bees can get.
The study, “Deformed wing virus is a recent global epidemic in honeybees driven by Varroa mites,” showed that mites which infected European honeybees (Apis Mellifera) became a global vector for the disease as pollinators spread with agricultural intensification after World War II. Hives increased 45 percent globally, but along with the bees, the mite travelled as well, jumping first from Asia to Europe, from Europe to the Americas, and from there to Australia, and recently to Hawaii and New Zealand, turning the disease into a global pandemic. The researchers used genetic tools to study the evolution of the disease globally and uncover its path of transmission.
Deformed wing virus is endemic in European honeybees and by itself isn’t deadly. “The virus alone is equivalent to a low level cold, not something that will kill you,” said lead author Lena Wilfert, of the University of Exeter’s Centre for Ecology and Conservation, in an interview. But when the mite appears, the virus turns fatal. The mites feed on bee larvae and spread the disease, which in turn kills overwintering bees.
Wilfert said the study showed that while the disease was largely man-made, measures could prevent or minimize its impact. Cross-border regulations that currently exist have to be more strictly enforced, and beekeepers need to take precautions to reduce mites during the winter — though Wilfert said such work was labor intensive.
These efforts are especially important because the disease has now spread to wild pollinators, such as bumblebees, which are not subject to such control measures.
Senior author Mike Boots, a professor at Exeter and UC Berkeley, added in a statement: “The key insight of our work is that the global virus pandemic in honeybees is manmade not natural. It’s therefore within our hands to mitigate this and future disease problems.”