Oak trees are among the highest natural emitters of isoprene, releasing large amounts especially during hot, sunny days. (Photo courtesy of Michigan State University)

MARQUETTE — A powerful natural bug repellent is hiding in some of our plants, but Michigan State University researchers said it may also be making our air dirtier, raising new concerns about crop science and climate.

The chemical is called isoprene and it helps plants fight off insects. Researchers said it does not kill bugs directly but triggers a hormone that makes the plant harder to digest. It is good news for the plant but bad news for the atmosphere.

Thomas Sharkey, professor of botany at Michigan State University, who led the study, is an expert on isoprene.“When you mix hydrocarbons such as isoprene with nitrogen oxide, and sunlight is present, then it makes ozone,” Sharkey explained. “More hydrocarbons are coming from plants than all of the manmade hydrocarbons.”

Sharkey pointed out fewer than half of plants produce isoprene and some labeled “non-emitters” actually do. He noted he hopes his research will help determine when it is useful to harness isoprene for pest control and when it is not.

MSU researchers said the findings could change how people grow food, balancing plant resilience with air quality. Sharkey shared what he called the most surprising part of the entire study. In 2022, there was a twist in the research that changed what scientists thought they knew about a familiar crop.

“We thought for a while that soybean didn’t have the required enzyme,” Sharkey recounted. “But we discovered that it did have the required enzyme and then we from there quickly discovered that, in fact under these certain conditions, we could cause it to make isoprene.”

Sharkey worries as heat waves become more common, soybeans could end up pumping more isoprene into the atmosphere, compromising air quality.