Flowers as dirty doorknobs: Deformed wing virus transmitted between Apis mellifera and Bombus impatiens through shared flowers

Abstract

In light of bee declines, the importance of pollination services from managed and native bees to our agriculture and economy is of great political, scientific and public interest. Viruses, first observed in honeybees, have been documented in bumblebees and the prevalence and load of some RNA viruses have been associated with managed honeybees. Shared flowers may be the bridge across which viruses pass between bees but no study has yet demonstrated that bumblebees can pick up viruses while foraging on contaminated flowers. Here, through a series of mechanistic laboratory experiments and mathematical modelling, we ask whether viruses can be transmitted between bee genera on shared flowers and how transmission can be effectively mitigated. We demonstrated that deformed wing virus (DWV) can be transmitted from infected honeybees to bumblebees through the use of shared red clover. We were also able to show that the route may work in reverse and bumblebees could contribute to the spread as well. Our model showed that reducing vector‐mediated transmission in honeybee colonies could potentially lead to a far greater reduction in bumblebee infection than simply reducing the number of honeybees. Additionally, we identified a dilution effect, whereby increasing floral abundance reduced transmission. Synthesis and applications. In this study, we showed that DWV may be spread between bee genera through the shared use of flowers. Through mathematical simulation, we identified two practical management options for reducing spread. The combination of treating honeybees effectively for the Varroa mite, a known vector of DWV, and increasing floral abundance where honeybees and native pollinators share the landscape were shown to reduce the spread of DWV within bee communities in simulations.

Honey bees and climate explain viral prevalence in wild bee communities on a continental scale

“…Although both the AKI-virus complex and SBPV can also be vectored and amplified to lethal levels in honey bee colonies by V. destructor , these viruses are more commonly found in wild bees 20 , 59 , 61 , 68 , 69 , suggesting key differences in host susceptibility and competence between these three viruses. The strong relations found in our study between viral prevalence in honey bees and wild bees together with the results from previous studies 19 , 55 highlight the need for good beekeeping practices, which include proactive varroa monitoring and control by beekeepers as well as appropriate hive placement, where the beekeeper takes into account the presence of endangered wild bees, to prevent managed honey bee colonies becoming sources of virus amplification and dissemination to wild bees 19 , 55 , 70 .…”

“…Interestingly, the effects of managed honey bee viral prevalence on wild bee viral prevalence did not differ between bumble bees and solitary bees, despite their different lifestyles and social organization, thereby underlining the importance of interspecific pathogen transmission, e.g. via shared floral resources 16 , 39 , 42 , 54 , 55 . Even though some solitary bee species are dietary specialists, visiting flowers of only a few plant species, the presence of generalist species such as honey bees connect many species in one network module, increasing the likelihood of viral transmission to all bee species present in the same environment 56 – 60 .…”

“…However, in contrast to wild bees, honey bees face the additional pressure of the parasitic mite Varroa destructor , which besides its virus-vectoring capacity can also weaken colonies, increasing the impact of viral infections 66 , 67 . A recent study highlighted the role of V. destructor in the transmission dynamics of DWV 55 . Incorporation of within-honey bee colony transmission, mediated by V. destructor vectoring and bee-to-bee transfer into a transmission model could explain the higher DWV prevalence in managed honey bees compared to wild bumble bees observed in the field 55 .…”

“…A recent study highlighted the role of V. destructor in the transmission dynamics of DWV 55 . Incorporation of within-honey bee colony transmission, mediated by V. destructor vectoring and bee-to-bee transfer into a transmission model could explain the higher DWV prevalence in managed honey bees compared to wild bumble bees observed in the field 55 . These results may also explain why we only observed DWV in wild bees when its prevalence in honey bees was high and the environmental viral load is likely to have been high.…”

Experimental cross species transmission of a major viral pathogen in bees is predominantly from honeybees to bumblebees

“…Moreover, in laboratory assays with genetically labelled DWV, Gusachenko et al [26] were able to demonstrate that DWV actively replicates when injected into the Western Palearctic Bombus terrestris (see also [27]) but failed to demonstrate viral acquisition and replication by feeding, questioning the spillover of DWV from honeybees to bumblebees through shared resource use at flowers in the field. In a more recent series of flight cage experiments with B. impatiens and DWV, Burnham et al [28] have now demonstrated the potential for viral transmission from honeybees to bumblebees as well as transmission from Bombus back to Apis; DWV-infected honeybees deposited DWV onto red clover (Trifolium pratense), B. impatiens foraging on DWV-infected flowers became infected with DWV, and DWV-infected B. impatiens themselves deposited DWV onto artificial flowers in a laboratory setting. It is unclear whether differences among studies in the potential for transmission of DWV (from Apis to Bombus) reflect the choice of Bombus species or experimental paradigm.…”