Wild bees face heightened environmental challenges in cities: Canadian study

A bee collects pollen from a crocus flower as it blooms along the Sir George-Etienne Cartier Parkway in Ottawa on Monday, April 11, 2022. THE CANADIAN PRESS/Sean Kilpatrick

Researchers from York University have found that wild bees living in cities like Toronto encounter growing environmental challenges, such as more pathogens and parasites, compared to rural and even suburban areas.

The researchers published their findings last Friday in in the journal Global Change Biology. They say alterations in the microbiomes of these bees in urban and fragmented habitats pose challenges to their access to food, suitable nesting spots, and potential mates.

These environmental stressors will likely increase as cities expand in the future, the researchers warn, noting that two-thirds of the world’s population will be living in cities by 2050.

“Having less connected habitats in dense urban areas not only leads to more inbreeding, so less genetic diversity, but it also creates higher pathogen diversity leaving city bees exposed to more pathogens,” corresponding author and associate professor Sandra Rehan of the York University’s Faculty of Science said in a news release published on Tuesday.

The data comes from an experiment that employed the whole genome sequencing of 180 common carpenter bees (Ceratina calcarata) in order to investigate their population genetics, metagenome, and microbiome, as well as the impact of environmental stressors across the Greater Toronto Area.

The carpenter bees are wild and native, distinct from managed and non-native bees like honeybees, the study notes.

Researchers observed notable variations in the microbiomes and availability of nutritional resources among bees in different environmental conditions even in the absence of genetic differentiation.

“Parasite and pathogen infections in bees are a major driver in global bee population declines and this is further exacerbated by urbanization and a loss of habitat and degraded habitat. There are things, though, that cities could do to help wild bees,” lead author and York University Ph.D. student Katherine D. Chau said in the release.

Researchers warn that cities that create an “urban heat island” effect with higher temperatures could impact all insect pollinators including bees which pollinated more than 87 per cent of flowering plants and 75 per cent of food crops globally.

With the identification of numerous bee and plant pathogens in densely urbanized regions, researchers say that these findings open up avenues for the early detection and surveillance of threats to wildlife within cities.

Reporting for this story was paid for through The Afghan Journalists in Residence Project funded by Meta.