Date Published: June 26, 2019
Publisher: Public Library of Science
Author(s): Samantha A. Alger, P. Alexander Burnham, Humberto F. Boncristiani, Alison K. Brody, Olav Rueppell.
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.
Many infectious diseases are caused by generalist pathogens that infect multiple host species . For pathogens capable of infecting multiple hosts, spillover occurs when the pathogen is introduced and transmitted from a reservoir population into a naive host population. Pathogen spillover between managed and wild animals causes species declines, threatens global biodiversity, and alters ecosystem function and services [2,3].
We detected BQCV in 75.7% and DWV in 9.3% of bumblebees tested (Table 1). We did not detect Israeli acute paralysis in any of the bees. The virus prevalence in honeybees was 100% for both BQCV and DWV, and loads ranged from 106 to 109 for BQCV and 104 to 1010 for DWV. Honeybee DWV loads followed a bimodal distribution (S1 Fig) with clear separation between two groups which we designated as either having “low” (< 107 genome copies) or “high” (> 107 genome copies) virus loads. The prevalence of BQCV was significantly higher in B. bimaculatus (86.3%) compared to B. vagans (65.9%) (χ12 = 15.671,P<0.001) but DWV prevalence was similar in both bumble bee species (χ12 = 0.263,P = 0.608; Table 2). The higher prevalence of both BQCV and DWV in bumblebees near honeybee apiaries, the lack of finding DWV in bumblebees at sites without honeybees, and the presence of viruses on flowers collected only from sites with apiaries, provide strong support for the hypothesis that RNA viruses are spilling over from managed honeybees into wild bumblebee populations through the use of shared floral resources. Source: http://doi.org/10.1371/journal.pone.0217822