By Scout Nelson
Research conducted by the University of Minnesota highlights how roadside areas may serve as valuable habitats for pollinators while also raising questions about pollution risks. Scientists study how environmental pollutants, especially microplastics from vehicle tires, affect insects such as butterflies and caterpillars that depend on roadside plants.
Pollinators like bumblebees and butterflies play an important role in ecosystems because they help plants reproduce. However, many pollinator populations have declined over recent decades. To help protect these species, transportation agencies and ecologists explore ways to restore roadsides as pollinator habitats.
Roadside land provides an opportunity because it often remains unused for farming, livestock grazing, or development. In states like Minnesota, roadsides already support plants such as milkweed, which provide food for many pollinators.
Despite these benefits, scientists question whether pollution near highways could harm insects. Emilie Snell-Rood, professor of ecology, evolution, and behavior at the University of Minnesota, explains the concern.
“Roadsides have a lot of potential as pollinator habitat. At the same time, though, we worry that they could be an ecological trap,” said Emilie Snell-Rood, professor of ecology, evolution, and behavior at the UMN and the study’s lead.
Roadside environments can contain several pollutants, including lead, gasoline residues, heavy metals from brake pads and tires, agricultural pesticides, and excess sodium or nitrogen. These substances may affect insects feeding on roadside plants.
For nearly a decade, researchers funded by the Minnesota Department of Transportation and the Minnesota Environment and Natural Resources Trust Fund have studied pollution levels along roadsides. One major focus involves microplastics from tire wear, which can settle on nearby vegetation.
Scientists discovered that small tire particles make up about 3.6 percent of the dry mass of milkweed leaves in some roadside areas. Because caterpillars feed on milkweed, researchers test how these particles affect insect health.
In laboratory experiments, researchers mixed different levels of ground tire particles into the diets of cabbage white caterpillars. The study included 400 caterpillars with microplastic levels ranging from zero to 16 percent of their diet.
Results show that caterpillars tolerate microplastic levels of up to eight percent without major effects on survival or development. Researchers find similar results when repeating the tests with monarch caterpillars.
While scientists continue studying possible effects on body size, reproduction, and lifespan, early findings offer encouraging signs for roadside habitat programs.
“The levels of microplastics that we’re seeing on the leaves do seem to be below thresholds of concern for caterpillars, at least in respect to survival and development time,” Snell-Rood said.
Even with these positive results, researchers stress that pollution control remains important. Snell-Rood emphasizes that roadside habitat development should continue alongside efforts to reduce environmental contamination.
“This is good news, but not a license to pollute,” Snell-Rood said.
Photo Credit: istock-herreid
Categories: Minnesota, General