There’s a new invasive insect taking aim at Wisconsin trees: the elm zigzag sawfly (EZS).

The pest, named for the distinctive zigzag pattern its caterpillars chew in elm leaves, had its first Wisconsin sighting in Portage County on July 4. As of Aug. 13, the insect has since been detected in at least 17 Wisconsin counties.

Originally from Eastern Asia, the elm zigzag sawfly was first detected in the U.S. in 2021 in Virginia.

In many cases, elm zigzag sawfly causes only minor or cosmetic damage to elm trees. However, levels of damage can vary significantly, and the insect does carry the potential to cause significant defoliation.

All elm zigzag sawflies are female and reproduce parthenogenically (without the need for mating). The insect sometimes has multiple generations in a single year, with new generations sometimes continuing their attacks on the same tree. Observers have noted up to four generations in a year in some states (even more in Europe).

Elm zigzag sawfly cocoons are sticky and can attach to human-made items such as vehicles and patio furniture. Even without hitching a ride, adults can travel more than 50 miles in a year.

In many cases, the presence of elm zigzag sawfly should not be a cause for alarm for landowners and foresters. Careful monitoring is recommended, and management may be warranted to help preserve the health of high-value trees.

The Wisconsin Department of Agriculture, Trade and Consumer Protection reports that there are no current or planned federal or state quarantines for elm zigzag sawfly.

Find more info on the elm zigzag sawfly from the University of Wisconsin-Madison Extension: https://hort.extension.wisc.edu/articles/elm-zigzag-sawfly/

From the Facebook of: Wisconsin Department of Natural Resources