A new Safeguard study examines the direct and indirect mechanisms that shape viral pathogen transmission between managed honey bees and wild pollinators.
The study investigates whether honey bees act as a reservoir host for several widespread pollinator viruses - specifically black queen cell virus (BQCV) and deformed wing virus (DWV-A and DWV-B). It also explores how overlap in floral resource use influences viral transmission, and how broader landscape factors such as urbanisation and agricultural intensification modify these dynamics. Few previous studies have addressed these questions holistically by considering host identity, plant-pollinator network architecture, and landscape structure simultaneously.
The findings confirm earlier research showing that honey bees are the dominant reservoir hosts of both BQCV and DWV, and the primary drivers of viral prevalence in wild pollinators. However, the study shows that viral density within honey bee colonies matters far more than honey bee density itself. This suggests that improving hive management and colony health to control pathogens is more effective for reducing transmission risks to wild pollinators than limiting honey bee numbers alone.
Floral niche overlap also emerges as a key transmission mechanism. BQCV transmission increases with overlap in flower use between honey bees and wild pollinators, largely independent of how infected honey bees are. DWV transmission, by contrast, is more strongly associated with high viral loads in honey bees, with floral overlap becoming important primarily under those conditions. This distinction highlights that pollinator viruses follow different transmission dynamics and cannot be easily generalised.
The study identifies a dilution effect: greater wild pollinator abundance reduces viral prevalence, particularly for DWV-B. Species richness alone does not appear to have the same effect. Many wild pollinators are poor-quality hosts for DWV-B, which reduces effective transmission chains.
Landscape context further shapes these processes by restructuring transmission networks. In urban landscapes, BQCV prevalence increases in managed honey bees but decreases in wild pollinators. The authors suggest this pattern may be driven by greater floral heterogeneity in cities, which reduces repeated and predictable flower sharing and fragments interaction pathways among pollinators. As a result, even when honey bees carry high viral loads, transmission to wild pollinators appears less efficient.
Overall, the authors conclude that reducing viral load in honey bees through improved colony health practices is currently the most effective strategy for lowering viral prevalence in wild pollinator communities.
Read the full study here.