Back to July 2020 Newsletter

Bee Viruses

Kim Fellows

The original intent of this bulletin article was to review the 13th annual Pollination Guelph Symposium, which would have taken place on Saturday March 14th, 2020. However, in an effort to slow the spread of COVID-19, the event was cancelled. So the focus this month is: are bees affected by viruses?

Yes, bees can be affected by viruses. Such viruses include acute bee paralysis virus, black queen cell virus, deformed wing virus, Lake Sinai viruses, sacbrood virus, chronic bee paralysis virus and many more. Bee viruses can be transmitted amongst several bee species, and susceptibility seems to be affected by nutritional status, host genetic composition, host sex, and bee age. Viral infections in bees can cause a range of deformities, systemic infections, reduced reproduction, and death. Honey bees are prone to a destructive parasite called the Varroa destructor mite, that can serve as a vector for many viruses.

Viruses are most commonly spread by shared floral resources. Infected bees can shed viruses on flowers as they forage, and these viruses can then infect other bees that visit these flowers. In the case of honey bees, infected foraging bees might also transmit the Varroa parasite (plus the viruses it carries) to foragers from other honey bee colonies. Infected members of social species, such as honey and bumble bees, can transmit the virus when they return to their colonies. And events such as the spring pollination of the almond crop in California, where almost all commercial hives are trucked, are opportunities for pathogenic transmission.

It appears that bee viruses are transmitted from wild bees to managed bees and from managed bees to wild bees. A recent study showed that wild bumblebees pick up more viruses the closer they forage to managed honey bee colonies. While viruses in particular have not been implicated in the following examples, it is pathogen spillover from commercial apiaries that is believed to be at least partly responsible for the decline of the rusty-patched bumble bee (now endangered) and another species at risk, the gypsy cuckoo bumble bee.

Could bees, like tigers, be afflicted by COVID-19 in particular? Apparently not. In order to replicate, viruses need to use the resources of the host’s cells, by first attaching to a site on the cell called a receptor. The coronavirus that causes COVID-19 uses a receptor which is found in cells in the respiratory and gastrointestinal tract of mammals. Bees are insects, in the phylum Arthropoda, and thus lack these receptors. However, it is interesting to note that Tobacco ringspot virus is a plant virus which can infect and replicate in the western domesticated honey bee. Little else is known about which plants and bees share similar viruses, serve as hosts to the same viruses, or serve as vectors of plant viruses.

How do bees resist viruses? Not much is known, although it has been reported that bees consuming higher-protein diets have lower viral loads. Bees' immune systems are capable of taking care of infections, as long as they have access to high quality forage (nectar and pollen) and their health hasn’t been compromised by pesticide exposure or other pathogens. And while it may seem evident that solitary bees might have an advantage over the social bees as far as physical-distancing measures go, bees need to go to the grocery store to survive.

Bee well.

--

Photo: Honey bee with deformed wing virus and Varroa destructor,  Creative Commons CC0 1.0

Back to July 2020 Newsletter