Floral resources shape parasite and pathogen dynamics in bees facing urbanization

Abstract

Urbanization is associated with increases in impervious land cover, which alters the distribution of resources available to wildlife and concentrates activity in unbuilt spaces such as parks and gardens. How resource shifts alter the dynamics of parasite and pathogen transmission has not been addressed for many important species in urban systems. We focus on urban gardens, resource‐rich “islands” within the urban matrix, to examine how the availability of floral resources at local and landscape scales influences the prevalence of six RNA viruses and three parasites in honey bees and bumble bees. Because parasites and pathogens are transmitted at flowers between visitors, we expected that floral abundance would concentrate bees within gardens, amplifying infection rates in pollinators, unless increases in floral resources would enhance bee diversity enough to dilute transmission. We found that garden size and flowering perennial plant abundance had a positive, direct effect on parasite and pathogen richness in bumble bees, suggesting that resource provisioning amplifies transmission. We also found that parasitism rates in honey bees were positively associated with parasites and pathogens in bumble bees, suggesting spillover between species. Encouragingly, we found evidence that management may mitigate parasitism through indirect effects: garden size had a positive impact on bee diversity, which in turn was negatively associated with parasite and pathogen richness in bumble bees. Unexpectedly, we observed that that parasite and pathogen richness in honey bees had no significant predictors, highlighting the complexity of comparing transmission dynamics between species. Although floral resources provide bees with food, we suggest more research on the tradeoffs between resource provisioning and disease transmission to implement conservation plantings in changing landscapes.

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

“…For example, Daughenbaugh et al [ 81 ] showed that the probability of AnBV-1 infection in honeybees is greater in habitats with low floral diversity, and suggest that between-species transmission is modulated by local floral community. Recently, Cohen et al [ 82 ] found that bee diversity reduced the parasite and pathogen richness in bumblebees in urban gardens, a dilution effect, even though the provision of resources (i.e. the size of gardens and the abundance of perennial plants) itself was associated with higher parasite and pathogen prevalence, an amplification effect.…”

Urban habitat fragmentation and floral resources shape the occurrence of gut parasites in two bumblebee species

“…Hence, PCR methods are suitable for screening and could provide detailed insights into the role of urbanization in pollinator epidemiology and pollinator-parasite interactions (Cohen et al, 2022).…”

Occurrence of Honey Bee (Apis mellifera L.) Pathogens in Wild Pollinators in Northern Italy

“…As many pollinators exploit the same floral resources as honey bees, horizontal transmission of pathogens, especially honey bee pathogens ( Dalmon et al., 2021 ), becomes possible with other Hymenoptera species ( Santamaria et al., 2018 ; Purkiss and Lach, 2019 ; Gusachenko et al., 2020 ; Ocepek et al., 2021 ), other pollinators ( Bailes et al., 2018 ), and other arthropods ( Nanetti et al., 2021a ). Considering the importance of wild pollinators and the adaptive plasticity of pathogens transmitted via regular flower visits ( Burnham et al., 2021 ; Cohen et al., 2022 ; Manley et al, 2019 ), our understanding of both ecosystem health and its impact on pollinator decline requires increased research on the interspecific interactions occurring in these ecosystems. The increasing number of studies reporting honey bee pathogens in other host species portrays a scenario consisting of one reservoir species and multiple spillover events.…”