New research in Nature: Disease associations between honeybees & bumblebees as a threat to wild pollinators

Emerging infectious diseases (EIDs) pose a risk to human welfare, both directly1 and indirectly, by affecting managed livestock and wildlife that provide valuable resources and ecosystem services, such as the pollination of crops2. Honeybees (Apis mellifera), the prevail- ing managed insect crop pollinator, suffer from a range of emerging and exotic high-impact pathogens3,4, and population maintenance requires active management by beekeepers to control them. Wild pollinators such as bumblebees (Bombus spp.) are in global decline5,6, one cause of which may be pathogen spillover from managed polli- nators like honeybees7,8 or commercial colonies of bumblebees9. Here we use a combination of infection experiments and landscape- scale field data to show that honeybee EIDs are indeed widespread infectious agents within the pollinator assemblage. The prevalence of deformed wing virus (DWV) and the exotic parasite Nosema ceranae in honeybees and bumblebees is linked; as honeybees have higher DWV prevalence, and sympatric bumblebees and honeybees are infected by the same DWV strains, Apis is the likely source of at least one major EID in wild pollinators. Lessons learned from vertebrates10,11 highlight the need for increased pathogen control in managed bee species to maintain wild pollinators, as declines in native pollinators may be caused by interspecies pathogen trans- mission originating from managed pollinators.

Trading practices in domesticated animals enable infectious dis- eases to spread rapidly and to encounter novel hosts in newly sympa- tric wildlife12. This ‘spillover’ of infectious disease from domesticated livestock to wildlife populations is one of the main sources of emerging infectious disease (EID)13. Small or declining populations are particu- larly challenged, as the source host may act as a disease reservoir14, giving rise to repeated spillover events and frequent disease outbreaks that, in the worst case, might drive already vulnerable or unmanaged popula- tions to extinction14. Such severe impacts have been well documented over the past decades in vertebrates10, but have largely been overlooked in invertebrates15. Recent years have seen elevated losses in multiple populations of one of the major crop-pollinating insects, the honeybee (Apis mellifera)16. EIDs have been suggested as key drivers of decline, and deformed wing virus (DWV) (particularly in combination with the exotic Varroa mite (Varroa destructor)) and Nosema ceranae are two likely causes for losses of honeybees17. As generalist pollinators, honeybees are traded and now distributed almost worldwide for crop pollination and hive products. They share their diverse foraging sites with wild pollinators and thus facilitate interspecific transmission of pathogens, as has been suggested for intraspecific disease transmission from commercial to wild bumblebee populations18. Our focus is on inter- specific transmission, as EIDs in managed honeybees are a potential threat to a range of wild pollinators worldwide. Although evidence from small-scale studies suggests that wild pollinators like Bombus spp. may already harbour some honeybee pathogens7,8,19,20, the true infectivity and landscape-scale distribution of these highly virulent EIDs in wild pollinator populations remains unknown. Read full article