The question ‘What is killing the bees’ has been baffling scientists in recent years. Several reports have talked about the mysterious drop in honeybee populations worldwide, with study focusing on likely causes, including parasites, a kind of pesticide known as neonicotinoids, and other factors.

Now, a research by the University of Exeter in the UK and the University of California, Berkeley, has come up with another explanation that the spread of a viral disease, accidentally helped along by human beings.

Published in the journal Science, the study has discovered that European honeybees are the key source of Deformed Wing Virus, which has spread via bee hives worldwide. The researchers have discovered that the spread of this insect pandemic has been majorly triggered by human trade and transportation of bees.

The disease is carried by the Varroa mite, feeding on bee larvae. Later, the virus itself kills off the bees.

The lead author of the study, Dr. Lena Wilfert, of the University of Exeter's Centre for Ecology and Conservation, mentioned that they have found proof that human involvement has played a main part in the epidemic.

In a press statement, she said, “If spread was naturally occurring, we would expect to see transmission between countries close to each other, but found that, for example, New Zealand virus population originated in Europe. This significantly strengthens theory that human transportation of bees is responsible for spread of devastating disease”.

The researchers examined sequence data of the virus samples gathered worldwide from virus carrying bees and the mites.

With the help of data, they built a path of how the virus spread, and came to know that it took a route from Europe to North America, Australia, and New Zealand. No movement was noticed between Asia and Australia, however, there was slight back-and-forth between Europe and Asia.

After examining other species of bees, they came to know that the European honeybee was to be mainly blamed for the virus’s spread.