A North American pest is recognizing that acres and acres of the Corn Belt’s soybean fields could become its next food source as it migrates south from Canada into Minnesota and the Dakotas, with eyes potentially on Iowa soon.

University of Minnesota entomologist Robert Koch said the soybean tentiform leafminer has moved into the Upper Midwest, laying eggs on the underside of soybean leaves that then hatch in the leaves.

As the larvae (caterpillar) lives and feeds within the leaves, it tunnels through the leaf tissue, leaving what Koch describes as “mines,” hollowed out areas that can damage and kill leaf tissue.

“This is a native insect that feeds on a couple vining forest legumes throughout much of eastern North America,” Koch explained. “I’m not aware of any confirmed detections in Iowa soybeans. So far, we have found this insect in soybeans throughout much of Minnesota and into the eastern Dakotas.”

Koch said he’s working to secure federal funding to support a coordinated survey effort across several states to determine how widespread the pest has migrated. Researchers are currently conducting lab studies to learn more about the insect.

Transition to soybeans

Koch said he’s curious to investigate why the insect has transitioned to feed on soybeans. “A simple hypothesis about this is that if some individuals somehow developed the ability to feed on soybeans, they would suddenly be surrounded by millions of acres of food instead of just the scattered native plants that they used to feed on in wooded areas,” Koch said. “A change like this could potentially be a big benefit to such individuals.”

While the leafminer was discovered in Canada in 2016, it wasn’t until 2021 that it was uncovered across Minnesota and in South Dakota.

Iowa farmers are encouraged to scout for the insect, especially along field edges near wooded areas. If discovered, contact local extension personnel for further review.

Treatment could include chemical control, host-plant resistance or biological control.

“We are evaluating a couple different insecticides for control of this pest,” Koch said. “Because the insect lives inside the leaves and could be protected from some applications, we are ev­­aluating foliar application of products that have translaminar activity, the ability to move through the leaf tissue.”

Different species of legume crops have been screened, and the pest is specific to soybeans, he said. “Our next step is to screen different varieties of soybeans that are known to be resistant to other pests to see if they might be resistant to this pest,” Koch explained.

“We are also evaluating the potential for biological control of the pest. We have found even though this pest hides inside the soybean leaves, it is attacked by several different species of parasitic wasps. 

“Interestingly, these tiny parasitic wasps lay their eggs on or in the pest insect, and then the egg of the wasp hatches into a larva that will feed on and eventually kill the pest,” he said.