From bees to sequencer: tracking pollinator viruses in Wellies
Here we are, early spring in Oxfordshire. The sun is rising and a beautiful day is forecast. It’s time for field work. In the village of Wantage, we established our HQ in an Airbnb. In the garden, the hairy-footed flower bees, Anthophora plumipes, are already busy foraging. I should say, females Anthophora are busy foraging. Males seem to have other type of business in mind. Over breakfast, Toby Doyle, research technician, Sophie Hedges, Master student, and myself are discussing about our field site for the day, and speculate on if the blackthorns and willow trees will be in bloom, and bet a beer on whether rape will also be in bloom or not. We pack the van, set up the sat nav, and drive towards one of the ten farms we will be visiting within two weeks.
The reason for our breakfast discussion about flowers lies less in our interest for plants, and more in the flower visitors, bees and flies, and the microbes they may carry. The goal of our field work is to collect insects and their parasites, or in other words, bugs in bugs. Thus, for ten days, we are collecting hundreds of insect pollinators, and will carry them to the lab to finally get to sequence their viruses.
The overarching aim of our project is to understand the role of flower diversity and density on disease transmission between pollinators. To test the hypothesis that more flowers may lead to more disease transmission, we specifically selected five farms with increased summer foraging resources for bees (following the High Level Stewardship agri-environmental scheme), and five control farms with no additional flowers. In addition to our insect collection, we also record flower visitation networks and measure flower density and diversity.
Farmland habitat restoration for pollinators have a profound effect on bee populations. Recently, Claire Carvell et al. shown in their publication in Nature that such agricultural management has a tremendous effect on bumble bees’ fitness. Using a capture-and-release method, and collecting a small piece of leg for molecular identification of individuals, Carvell et al. followed the survival of family lineages of bumble bees across two years. Among other factors, the presence of early season foraging resources, such as cherry trees or willow, and of flower-rich field margins, was shown to ensure a successful production of offspring in comparison to less flower-rich habitats.
Consequently, if there are more bees nesting in more flower-rich habitats, one may expect from this crowd an increase of indirect contact between insects, via visitation on flowers for foraging. Thus, higher density of contact between potential hosts may increase disease transmission between pollinators. By superimposing high resolution flower-insect contact networks we are recording during our field work, and the insect-virus networks we will build from virus sequences analysis, we will determine in an unprecedented depth the complexity of the dynamics of pollinator viruses, and reveal whether agricultural landscape management may alter the epidemiology of bee diseases.
This field work is the end of our fourth sampling period within 12 months. After 10 days of collection, we will head back to our lab in Cornwall with lots of insect samples. It will be time for RNA extraction, and for the pollinator viruses to get ready for their last trip, from the lab to sequencer. While we are collecting our last samples by sweeping tree canopy with our nets, we are approached by walkers. The contrast is always striking, between the sweaty scientists, smelling of sun cream from miles away, and couples or families enjoying the country side, walking their dog towards the pub. But field work is also a unique opportunity to discuss with the public and we always welcome thoughtful questions from the curious onlooker.