Efforts to promote the future health of both wild bees and managed honeybee colonies need to consider specific habitat needs, such as the density of wildflowers, say researchers.

At the same time, improving other habitat measures—such as the amount of natural habitat surrounding croplands—may increase bee diversity while having mixed effects on overall bee health.

The findings are from a new analysis of several thousand Michigan bees from 60 species. The study looks at how the quality and quantity of bee habitat surrounding small farm fields affects the levels of common viral pathogens in bee communities.

“Future land management needs to consider that broadly improving habitat quality to benefit pollinator community diversity may not necessarily also benefit pollinator health,” says University of Michigan biologist Michelle Fearon, lead author of a study in the journal Ecology.

“To promote pollinator health, we need to focus on improving specific habitat quality features that are linked to reducing pathogen prevalence, such as planting greater density of flowers,” says Fearon, a postdoctoral fellow in the ecology and evolutionary biology department.

Pollinators and Pathogens

Bees are indispensable pollinators, supporting both agricultural productivity and the diversity of flowering plants worldwide. But in recent decades, both native bees and managed honeybee colonies have seen population declines, which are blamed on multiple interacting factors including habitat loss, parasites, and disease, and pesticide use.

As part of the work for her doctoral dissertation, Fearon and her colleagues netted and trapped more than 4,900 bees at 14 winter squash farms in southeastern Michigan, where both honeybees and wild native bees pollinate the squash flowers.

The bees were analyzed for the presence of three common viral pathogens. Consistently, lower virus levels were strongly linked to greater species richness, or biodiversity, among local bee communities. The number of bee species at each farm ranged from seven to 49.

Biodiversity and the 'Dilution Effect' 

Those findings, published in February 2021 in Ecology, provided support for what ecologists call the dilution effect. This controversial hypothesis posits that increased biodiversity can decrease, or dilute, infectious disease transmission.

But an unresolved question lingered after that study was published: Was biodiversity truly responsible for the observed reductions in viral levels, or was there something about habitat quality that drove changes in both bee biodiversity and viral pathogen prevalence?

Read the full article about biodiversity for bee habitat by Jim Erickson at Futurity.