The threat of pathogen spillover from introduced bees to native bumblebee populations in the UK

The UK's bumblebee populations are vulnerable, with 3 out of 25 species now extinct, 7 threatened and 15 having undergone major range contractions in recent years. The importance of bumblebees for crop pollination means their declines are of economic as well as conservation significance. Britians already vulnerable bumblebee populations face additional risks from emerging diseases. Approximately 60,000 bumblebee colonies are imported to the UK from continental Europe each year for the pollination of greenhouse crops, and these potentially carry with them exotic parasites. As the introduced bees frequently interact with native bumblebee populations, the threat of pathogen spillover is real and significant. Indeed, such pathogen spillover is thought to have been responsible for bumblebee declines in North America. In addition, there is evidence that honeybee viral parasites may be able to infect bumblebees. Some honeybee viruses are highly virulent, most recently being implicated in the 'Colony Collapse Disorder' syndrome which has caused substantial honeybee mortality. The threat of pathogen spillover from honeybees to bumblebees is therefore also real and significant and there may be the additional potential for introduced bumblebees to bring with them parasites detrimental to honeybees. However, there is still only very little data on which to base an assessment of these threats. This project aims to address this. It will use molecular methods to identify the diversity of parasites infecting introduced bumblebees and determine if they differ from British strains. Experimental exposures will determine if both intraspecific and interspecific pathogen spillover is possible, and the resulting virulence and transmission dynamics of the resulting infections. Cage trials will be used to prevent escape while mimicking the conditions in bumblebee rearing facilities. In parallel, and again using cage trials to prevent escape, the project will determine experimentally if three honeybee viruses are able to infect bumblebees and what impacts they have on their new hosts. Experiments will finally determine whether the viruses are then able to transmit between bumblebee hosts, or if they are reliant on mite vectors for this. The results will substantially add to our understanding of the level of risk posed by pathogen spillover to the UK's ecologically and economically important populations of bumblebees, and will provide the evidence for appropriate management strategies.