Bee viruses in bee-mimicking flies

The hoverfly (or syrphid fly) Eristalis interrupta (or nemorum), photo by James Lindsey in Belgium.

This week's paper is in Biology Letters, led by post-doc Emily Bailes from Royal Holloway University of London. Dr. Bailes examined the presence of honeybee viruses in hoverflies (also called syrphid flies as they are in the family Syrphidae). Syrphid flies first deserve some introduction of their own. The Syrphidae family is comprised of flies whose adult lifestages predominantly feed on flower nectar and pollen. What is particularly striking about them is their mimicry of other pollinators including a variety of bees and wasps. As a small example, the insects in the photos below are all flies!

Syrphid flies. Photos and layout by Joaquim Alves Gaspar. 

Although syrphid flies fill the same niche as bees (foraging from flowers), and look like bees, there has been little investigation of their role in the spread of pollinator diseases. It has been previously demonstrated that viruses originally found in managed honeybees can spread to wild native bees through visits to shared floral resources . The role of very ecologically similar, but evolutionarily distant, syrphid flies in disease dynamics had remained unexplored. Dr. Bailes and her colleagues collected 20 individuals each of honeybees and four species of syrphid fly at a long-term study site in England called Wytham Woods (famous for its research with great tits). Of the four syrphid flies, two species are honeybee mimics in the genus Eristalis that not only look like honeybees (see the first photo above) but also mimic honeybee behavior at flowers. The other two species were in the genera Episyrphus and Platycheirus and although they forage for nectar and pollen from flowers they do not look or act like honeybees. Dr. Bailes and her colleagues used RNA sequencing to determine the presence or absence of six common bee viruses in the honeybees and flies. They found bee viruses present in the two honeybee mimicking Eristalis, but not in Episyrphus and Platycheirus even though those flies are visiting flowers in the same habitat! The viruses that occured in Eristalis were in lower numbers than in honeybees, and had almost identical RNA sequences to the viruses from honeybees, indicating that the viruses may not be replicating in flies, rather the flies are picking them up from honeybees. The flies, however, may still be able to serve as vectors of the viruses even if they don't infect the flies. The extent to which these viruses are replicating in the flies (and negatively impacting the flies) is an area in need of further investigation. Also I really want to know more about why the viruses only occur in Eristalis. Are they more likely to have the viruses because they share more individual flowers with honeybees? Or is it because of something else about how they behave? I am fascinated by how behavior could be shaping disease transmission.