New invasive insect elm zigzag confirmed in Minnesota

A new invasive insect has been confirmed in Minnesota for the first time.

The state Department of Agriculture announced Tuesday that the elm zigzag sawfly was found on the University of Minnesota Twin Cities campus.

The insect — native to east Asia, and first found in the U.S. in 2021 — is named for the distinctive pattern that its larvae leave when feeding on elm leaves. Prior to this year, the insect’s spread in the U.S. had mostly been confined to states on the East Coast.

“The potential impacts of the elm zigzag sawfly are unknown because of the short period of time it has been present in the United States. Although the insect causes defoliation of elm trees, most defoliated trees can recover from a defoliation event,” the Minnesota Department of Agriculture said. “Best management practices are also unknown. However, since most trees can recover, management may not be necessary.”

The discovery of the elm zigzag sawfly in Minnesota stemmed from a citizen report on the iNaturalist platform for sharing nature observations.

State agriculture officials said an out-of-state college student studying the invasive insect saw that report, and Minnesota officials were notified. Experts at the Smithsonian Institute’s National Museum of Natural History.

The unique pattern of leaf damage left by larvae may be the easiest way to locate the insect. State agriculture officials said those larvae are “green with a black band on their head. They have T-shaped brown or black markings on the top of their second and third pair of legs.”

Experts at North Carolina State University created a website with more photos and information about elm zigzag sawfly.

Minnesota agriculture officials said they’re looking for the public’s help to determine where elm zigzag sawfly is in the state. Suspected sightings can be reported online on the state’s “Report a Pest” site, or by calling (888) 545-6684.