Road networks extend some 20 million miles across the globe, and that number is projected to increase by an additional 15 million miles or so by 2050.

Roads can be barriers to wildlife of all sorts, and scientists have studied road impacts on animals ranging from Florida panthers and grizzly bears to box turtles, mice, rattlesnakes and salamanders.

But much less is known about the impact of roads on pollinating insects such as bees and to what extent these structures disrupt insect pollination, which is essential to reproduction in many plant species.

In a paper published online May 10, 2021 in the Journal of Applied Ecology, University of Michigan researchers describe how they used fluorescent pigment as an analog for pollen. They applied the luminous pigment to the flowers of roadside plants to study how roads affected the movement of pollen between plants at 47 sites in Ann Arbor, Mich.

The researchers found that plants across a road from pigment-added plants received significantly less pigment than plants on the same side of the road. The study also suggests relatively simple ways to reduce this road-barrier effect.

“Our study shows that roads and paths pose a significant barrier to bee movement and therefore substantially reduce pollen transfer,” said study author Gordon Fitch, a doctoral candidate in the U-M Department of Ecology and Evolutionary Biology. His co-lead author is Chatura Vaidya, also an EEB doctoral candidate.

The study focused on two species of insect-pollinated flowering plants native to the region, wild bergamot (Monarda fistulosa) and threadleaf coreopsis (Coreopsis verticillata).

“Ours is the first well-replicated study to examine how roads impact bee movement,” Fitch said.

“Moreover, we used an innovative technique relying on pigment as a pollen analog—rather than direct observation of insect behavior—which allowed us to collect data efficiently. As such, we are also the first to show that roads disrupt the movement of pollen between plants.”

The study is receiving widespread media attention, including in Popular Science, Academic Times, the Applied Ecologists blog and on WEMU 89.1 NPR's Issues of the Environment.

Read full Michigan News press release