A spatially explicit model of pollinator-plant-pathogen interactions

Flowers have long been suggested to be infection hotspots for pollinator diseases, as, during their brief lifespan, they are visited and handled by many individuals from a diverse range of species. Evidence that floral hotspots are an important point of contagion is building, but few models currently allow us to characterise these novel plant-pathogen-pollinator systems where horizontal infections occur from concentrated, short-lived sites of contagion. Infection success is going to depend heavily upon the behaviour of individual pollinators, alongside the structure of the floral landscape that they are foraging within. Here, we describe an individual-based model that considers the impact of environmental heterogeneity and individual differences in movement on the spread of a disease that is spread via floral hotspots, considering a centrally nesting social pollinator (such as a social bee). The biggest effects we saw were associated with the likelihoods of leaving and staying in the nest and the distances travelled by the pollinators, and so it is likely that social pollinators, most of which are constrained to return to a central nest, could be strongly impacted by the schedules they use for allocating foraging behaviour. We also considered the impact of the pollinators being able to deposit and detect temporary scent-marks, which could inform an uninfected pollinator of a potentially infected site. Scent marks have a negative impact on pathogen transmission, and their effect may be dependent on both the longevity of the scent mark, the turnover of flowers in the environment, and the factors affecting pathogen viability and infectivity. Overall, although the structure of the landscape may have limited impact on pathogen spread, the behaviour of the pollinators is important, and needs further consideration within models of this pathogen system. AUTHOR SUMMARYFlowers have long been suggested to be infection hotspots for pollinator diseases, as, during their brief lifespan, they are visited and handled by many individuals from a diverse range of species. Evidence that floral hotspots are an important point of contagion is building, but we currently know little about the environmental biology of these infections. We describe a model that considers how pathogens caught at floral infection hotspots might spread in populations of social pollinators (such as a bumblebee or honeybee), and show that both pollinator behaviour and how flowers are distributed through the landscape can have a big impact on the spread of the pathogen. Pollinators can leave temporary detectable scent marks on the surfaces of the flowers that they visit: our model demonstrates that being able to detect these marks reduces the spread of the pathogen, as the pollinator is better able to avoid potential hotspots.