Conservation measures or hotspots of disease transmission? Agri-environment schemes can reduce disease prevalence in pollinator communities

Insects are under pressure from agricultural intensification. To protect
pollinators, conservation measures such as the EU agri-environment schemes
(AES) promote planting wildflowers along fields. However, this can
potentially alter disease ecology by serving as transmission hubs or by
diluting infections. We tested this by measuring plant-pollinator
interactions and virus infections (DWV-A, DWV-B and ABPV) across
pollinator communities in agricultural landscapes over a year. AES had a
direct effect on DWV-B, reducing prevalence and load in honeybees, with a
tentative general dilution effect on load in early summer. DWV-A
prevalence was reduced both under AES and with increasing niche overlap
between competent hosts, likely via a dilution effect. In contrast, AES
had no impact on ABPV; its prevalence was driven by the proportion of
bumblebees in the community. Epidemiological differences were also
reflected in the virus phylogenies, with DWV-B showing recent rapid
expansion, while DWV-A and ABPV showed slower growth rates and geographic
population structure. Phylogenies indicate that all three viruses freely
circulate across their host populations. Our study illustrates how complex
interactions between environmental, ecological and evolutionary factors
may influence wildlife disease dynamics. Supporting pollinator nutrition
can mitigate the transmission of important bee diseases, providing an
unexpected boost to pollinator conservation.