One giant leap for pathogen-kind.
This past week, the news has been buzzing* with the latest threat to honeybees, a virus which has jumped from the plant world to the insect world (although I found the exact same article at three different urls, so there’s not exactly a wealth of info out there). This is a fascinating story, because pathogens don’t usually jump from one kingdom to another!
The Tobacco Ring Spot Virus (TRSV) normally infects a wide variety of plants and can cause serious damage to crops. Its biggest impact has been on soybean crops, which can experience losses from 25-100% (source). Interestingly this virus seems to have a variety of transmission pathways, from vertical transmission through the seeds, to horizontal transmission through vectors like nematodes and thrips (Bergeson et al. 1964).
However, the mode of transmission we’re particularly interested in today is through pollen. Many plant viruses spread through pollen (kind of like an STD for plants, but that’s for another post). This is also how the virus came in contact with the honeybees.
Scientists found the virus to be systemic throughout honeybee hives that had already been classified as “weak”, as well as in the Varroa mites feeding on the honeybees (Li et al. 2014, open access).
A grain of salt to take with you on this story: as exceptional as it is to find the virus jumping from plants to animals, we still don’t know how the bees are affected by it, whether it actually causes losses in fitness, or whether it is a part of the CCD story. Because the virus is only found in colonies that are already weak, we don’t know whether it can infect healthy honeybees under normal conditions.
The bees are already stressed; that could make them the perfect host for an opportunistic jump from one kingdom to another.