Humans Didn't Cause the Honeybee Pandemic, But We Did Spread It Everywhere

Honeybees the world over are dying out. And now researchers have found that the continued deadly spread of a pandemic infecting hives, and decimating them, is caused by humans.

In a study published Thursday in the journal Science, researchers describe how a global pandemic killing off honeybees is driven by both the trade and transport of honeybees (Apis mellifera) from Europe to the rest of the world.

"It's been known for a while that the combination of Deformed Wing Virus (DWV) and the Varroa mite are really bad news for honeybees," explained Lena Bayer-Wilfert, lead study author and an evolutionary geneticist at the University of Exeter's Centre for Ecology and Conservation, over the phone. "We wanted to know how the diseases they cause had spread globally, and which populations are driving the epidemic at a global level."

Deformed Wing Virus is a disease that affects honeybees and other pollinators. The Varroa mite is a parasite that feeds on the blood of honeybee larvae. According to Bayer-Wilfert, these are two separate issues, both DWV and Varroa can cause honeybees to die off at breakneck speed. Humans are fueling the spread.

"We consider DWV a re-emerging disease because we have evidence that DWV was around in honeybees and other pollinators before the arrival of Varroa, but this new vector has lead to a new global epidemic," said Bayer-Wilfert. "This in turn is mainly driven by European populations of European honeybees."

Bayer-Wilfert explained that European honeybees would never have picked up Varroa from Asian honeybees in the first place, if it had not been for the human-assisted movement of European bee colonies from one region to another.

For their study, the researchers analysed Deformed Wing Virus sequencing data from samples collected from honeybees and Varroa mites. Their findings allowed them to see how the virus had spread from Europe to North America, Australia and New Zealand.

Bayer-Wilfert explained that the Apis mellifera had most probably been taken to countries outside of Europe in order to "encourage beekeeping in other areas, and to bring better hives to them." That, she explained, is how the Varroa mite managed to infest global honeybee networks.

Bees, said Bayer-Wilfert, only fly around ten kilometers away from their hive. This means that if bees had spread the pandemic themselves, it would have taken hundreds of years. The researchers findings showed that in some cases, these honeybee populations had moved across Russia within just over a decade. This fast movement strongly implied human involvement.

In order to contain the pandemic, Bayer-Wilfert recommended that beekeepers stick with the best practices they've upheld over the years. At an international level, in the last decade, many countries have brought in trade regulations that limit the movement of honeybees. This, however, still leaves no room for complacency.

"We've shown that a particular variant of DWV could spread globally very quickly. Viruses, however, evolve all the time, if there is a new variant arising, it could use the previously existing trade routes to spread just as fast again," she added.