Mass-flowering monoculture attracts bees, amplifying parasite prevalence

Abstract

As the global agricultural footprint expands, it is increasingly important to address the link between the resource pulses characteristic of monoculture farming and wildlife epidemiology. To understand how mass-flowering crops impact host communities and subsequently amplify or dilute parasitism, we surveyed wild and managed bees in a monoculture landscape with varying degrees of floral diversification. We screened 1509 bees from 16 genera in sunflower fields and in non-crop flowering habitat across 200 km 2 of the California Central Valley. We found that mass-flowering crops increase bee abundance. Wild bee abundance was subsequently associated with higher parasite presence, but only in sites with a low abundance of non-crop flowers. Bee traits related to higher dispersal ability (body size) and diet breadth (pollen lecty) were also positively related to parasite presence. Our results highlight the importance of non-crop flowering habitat for supporting bee communities. We suggest monoculture alone cannot support healthy bees.

Floral resources shape parasite and pathogen dynamics in bees facing urbanization

“…We suggest that morphological and physiological differences in traits between host species may drive parasite and pathogen colonization and persistence in this system. There is little literature on the role of bee host traits in epidemiology, but traits such as body size and diet breadth have been found to play a role in pathogen exposure (Cohen et al, 2021;Figueroa et al, 2019Figueroa et al, , 2020, probably by mediating bee behaviour at flowers harbouring parasites and pathogens. For example, bees with a broader diet breadth may visit more plant species and therefore risk exposure to a diversity of parasites and pathogens.…”

Understanding effects of floral products on bee parasites: Mechanisms, synergism, and ecological complexity

“…Similar patterns were found for initially pathogen-free commercial B. impatiens colonies deployed in farms that varied in the number of sunflower flower heads present (Malfi et al, unpublished data). However, in another recent study in commercial sunflower farms, C. bombi prevalence in wild caught bees (of multiple genera) trended higher in plots that were adjacent to sunflower fields compared to plots with no sunflower adjacent ( Cohen et al, 2021 ). This mixed evidence highlights the complexity of evaluating the effect of antiparasitic floral products in field conditions, where a multitude of other factors are operating to shape patterns of bee parasite prevalence and disease.…”

“…The authors suggest this pattern could result either from the improved nutritional status of bees in flower-added landscapes leading to better tolerance of parasites, or from the concentration of bees at small, resource-rich sites leading to high parasite transmission ( Piot et al, 2019 ). Similarly, in commercial sunflower plantings in California, USA, high bee abundance was linked to greater parasite prevalence at sites with low-to-average floral abundance, but to reduced parasite prevalence at sites with high floral abundance ( Cohen et al, 2021 ). And in another study across multiple habitats and two years in Pennsylvania, USA, the prevalence of N. bombi and several pathogenic viruses in B. impatiens was negatively correlated with the availability of early-season floral resources ( McNeil et al, 2020 ).…”

Pollen DNA metabarcoding and related methods in global change ecology: prospects, challenges, and progress

“…Expansions in agricultural land cover can have a range of impacts on pollinators (Potts et al, 2010), including decreasing floral resource diversity (Grab et al, 2019;Richardson et al, 2021), increasing pesticide exposure risk (Douglas, Sponsler, Lonsdorf, & Grozinger, 2020;Douglas & Tooker, 2015), and increased parasite loads (Cohen et al, 2021). Pollen DNA metabarcoding can show how pollinators respond to this changing agroecosystem and can be used to monitor changes.…”