Viruses of managed alfalfa leafcutting bees (Megachille rotundata Fabricus) and honey bees (Apis mellifera L.) in Western Canada: Incidence, impacts, and prospects of cross-species viral transmission.

We examined whether alfalfa leafcutting bees (ALCB, Megachille rotundata) experienced a higher incidence of seven viruses commonly found honey bees (Apis mellifera) when placed alongside honey bees for hybrid canola seed pollination. Although two viruses - sacbrood virus (SBV) and deformed wing virus (DWV) - were detected in ALCB adults, their presence appeared independent of whether honey bees were present in the same field or not. A further survey of viruses among ALCB adults in three different alfalfa seed growing regions in Western Canada confirmed the ubiquity of sacbrood virus (SBV) as well as the infrequent presence of acute bee paralysis virus (ABPV), both of which had not been previously reported on ALCB. Moreover, SBV and ABPV were detected in the cocoon stage and only in one region. Co-infection among pools of ALCB adults with both of these viruses was more closely correlated with decreasing levels of cocoon viability than infection levels in cocoons themselves. This research suggests ongoing viral transmission between honey bees and ALCB in the same fields is likely low but that co-infection with these viruses may lower ALCB productivity.

Higher prevalence of sacbrood virus in Apis mellifera (Hymenoptera: Apidae) colonies after pollinating highbush blueberries.

Highbush blueberry pollination depends on managed honey bees (Apis mellifera) L. for adequate fruit sets; however, beekeepers have raised concerns about the poor health of colonies after pollinating this crop. Postulated causes include agrochemical exposure, nutritional deficits, and interactions with parasites and pathogens, particularly Melisococcus plutonius [(ex. White) Bailey and Collins, Lactobacillales: Enterococcaceae], the causal agent of European foulbrood disease, but other pathogens could be involved. To broadly investigate common honey bee pathogens in relation to blueberry pollination, we sampled adult honey bees from colonies at time points corresponding to before (t1), during (t2), at the end (t3), and after (t4) highbush blueberry pollination in British Columbia, Canada, across 2 years (2020 and 2021). Nine viruses, as well as M. plutonius, Vairimorpha ceranae, and V. apis [Tokarev et al., Microsporidia: Nosematidae; formerly Nosema ceranae (Fries et al.) and N. apis (Zander)], were detected by PCR and compared among colonies located near and far from blueberry fields. We found a significant interactive effect of time and blueberry proximity on the multivariate pathogen community, mainly due to differences at t4 (corresponding to ~6 wk after the beginning of the pollination period). Post hoc comparisons of pathogens in near and far groups at t4 showed that detections of sacbrood virus (SBV), which was significantly higher in the near group, not M. plutonius, was the primary driver. Further research is needed to determine if the association of SBV with highbush blueberry pollination is contributing to the health decline that beekeepers observe after pollinating this crop.