RNA virus spillover from managed honeybees (Apis mellifera) to wild bumblebees (Bombus spp.)

Abstract

The decline of many bumblebee species (Bombus spp.) has been linked to an increased prevalence of pathogens caused by spillover from managed bees. Although poorly understood, RNA viruses are suspected of moving from managed honeybees (Apis mellifera) into wild bumblebees through shared floral resources. We examined if RNA viruses spillover from managed honeybees, the extent to which viruses are replicating within bumblebees, and the role of flowers in transmission. Prevalence and active infections of deformed wing virus (DWV) were higher in bumblebees collected near apiaries and when neighboring honeybees had high infection levels. We found no DWV in bumblebees where honeybee foragers and honeybee apiaries were absent. The prevalence of black queen cell virus (BQCV) was also higher in bumblebees collected near apiaries. Furthermore, we detected viruses on 19% of flowers, all of which were collected within apiaries. Our results corroborate the hypothesis that viruses are spilling over from managed honeybees to wild bumblebees and that flowers may be an important route for transmission.

Fig 1. Percent prevalence of infected bumblebee individuals for black queen cell virus (BQCV) and deformed wing virus (DWV).

Bumblebees were either caught in sites with honeybee apiaries present or no apiary nearby. BQCV and DWV were more prevalent in bumblebees caught in sites with a honeybee apiary present than in sites without an apiary nearby. Standard error bars are shown. Asterisks represent significance.

Fig 2. Percent prevalence for bumblebees infected with deformed wing virus (DWV) at sites where honeybees had high and low viral loads, and sites where no honeybees were present and therefore could not be collected.

DWV was more prevalent in bumblebees caught at sites with honeybees with high average viral loads, than sites with honeybees with low average viral loads. Standard error bars are shown.