COLUMBUS — A researcher recently discovered a population of the invasive elm zigzag sawfly infesting elm trees at the U.S. Department of Agriculture’s Forest Service Northern Research Station lab in Delaware and in northern Franklin County. The Forest Service and the Ohio Department of Natural Resources (ODNR) Division of Forestry report that subsequent surveys have also located the species on nearby properties.
“Elm zigzag sawfly is an invasive insect native to Asia that was first found in Canada in 2020 and in multiple eastern U.S. states in 2021 and 2022,” ODNR Division of Forestry, Forest Health Program Manager Tom Macy said. “This is the first detection of the species in Ohio.”
While capable of significant defoliation of elm trees, the overall impact of the species to forests and urban landscapes is not fully known and is an area of active research. There are no reports of the elm zigzag sawfly causing the death of elm trees. Management options for the species are still being studied. The ODNR Division of Forestry will continue to survey for the elm zigzag sawfly across the state.
The elm zigzag sawfly larva is up to one-half-inch long, caterpillar-like, and light green in color. The larvae feed exclusively on the leaves of elm trees—including native and introduced elm species. The larvae create a distinctive zigzag pattern through the leaves as they feed. Before pupating, the larvae spin loose, net-like cocoons attached to leaves. In the fall, they form more solid-walled overwintering cocoons on the ground in leaf litter or soil. Adults are less commonly observed but are small (0.25″ in length), shiny black, and winged.
“The Northern Research Station has conducted important research on Dutch elm disease-tolerant elm at the Delaware lab for several decades. Because we manage multiple acres of elm plantations and monitor them closely, we were able to detect this infestation of elm zigzag sawfly,” Northern Research Station Ecologist Kathleen Knight said. “Northern Research Station scientists worked with the appropriate regulatory agencies to confirm the identification of the insect and identify infested areas.”
A few elm zigzag sawfly larvae were noticed on trees in the nursery in early July and officially confirmed by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service on July 21. Subsequent surveys were quickly performed to understand the extent of the infestation, which led to identifying the insect on nearby properties. Elm zigzag sawfly was confirmed in Franklin County on Aug. 18. The Forest Service and ODNR prioritized accurate assessment of the situation and sharing knowledge as rapidly as possible.
If you find a suspected elm zigzag sawfly or signs of infestation, report the sighting using the free Great Lakes Early Detection Network mobile app or try to get a good photo or collect a specimen and notify the ODNR Division of Forestry at 614-265-6694.