Bee Conservation

Red-tailed bumblebees found to be key hosts for dangerous bee virus

Wild bumblebees serve as key hosts for acute bee paralysis virus. While the virus appears to cause little harm to bumblebees, infection is usually fatal to honeybees. Until now, it was assumed that honeybees were the key host for the virus. By using data from extensive field trials, a team from Martin Luther University Halle-Wittenberg (MLU) and Georg August University of Göttingen has now identified the red-tailed bumblebee as the key host for acute bee paralysis virus.

Their study is published in the journal Ecology Letters and could help inform policies that aim at curbing the spread of such diseases in nature.

Honeybees, wild bees and other insect species are connected by their shared visits to flowers. "A flowering summer meadow is therefore both a source of food and a potential site for the transmission of viral infections. This is because insects searching for food there come into contact with material that may be contaminated with viruses, such as pollen and nectar," says biologist Professor Robert Paxton from MLU.

Until now, research has assumed that honeybees serve as primary hosts for various viruses and can thus infect bumblebees and other wild bees. However, the new study paints a different picture: according to it, wild bees can also be reservoir hosts for viruses and thus theoretically contribute to the infection of honeybees.

This result is based on field data collected by the team at 32 locations in Lower Saxony and Hesse. The researchers first observed whether different bee species visit the same flower species. They also used virus screening of 1,725 insects comprising multiple bee species to analyze how much each bee species contributes to the spread of various viruses.

To identify the bee species that contribute the most to the spread of viruses, we used the basic reproduction number, R? This measure estimates how widely a virus can spread from one insect to others of the same species," explains Patrycja Pluta from MLU, lead author of the study.

The team calculated precisely for each combination of virus and bee species how easily a virus can spread and how much each bee species potentially contributes to the spread of viruses.

The researchers identified the most important host insects for three known bee viruses. They found that honeybees are the main carriers of deformed wing virus (DWV) and black queen cell virus (BQCV) at the sites studied.

"However, the main host insect for the acute bee paralysis virus is a wild bee: the red-tailed bumblebee Bombus lapidarius," says Patrycja Pluta. When honeybees become infected with the virus, they are unable to fly after a short time, start to tremble and die within a few days. This can lead to the rapid collapse of an entire colony.

Another finding: the composition of bee species at a location has less influence on the spread of viruses than previously assumed. In contrast, direct contact with bees that transmit many viruses plays a decisive role. And this occurs when visiting flowers.

According to Robert Paxton, these findings are important for understanding how diseases spread in nature and how they can possibly be counteracted.

"The more space and the more diverse food bees have, the less likely infections are to occur. To minimize the risk of further spread of disease, more flower strips with many different plant species would be very helpful, for example," says Paxton. DOI: 10.1111/ele.70327