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For Release: Monday, September 26, 2022

DEC Finds New Exotic Pest Affecting Elm Trees in St. Lawrence County

Surveys Underway to Determine Extent of Insect Populations and Potential Impact to Native Elms

The New York State Department of Environmental Conservation (DEC) today announced that the elm zigzag sawfly (Aproceros leucopoda) was detected for the first time in New York State at three locations in St. Lawrence County, including Wilson Hill Wildlife Management Area, Brasher State Forest, and Lost Nation State Forest. This exotic pest feeds exclusively on elm trees and can cause severe defoliation, branch dieback, and crown thinning. Although the sawfly has not yet been shown to cause tree mortality, repeated defoliation by established sawfly populations would put added stress on native elm trees already heavily impacted by Dutch elm disease.

"Assessing threats to the health of our forests and street trees is essential for maintaining the immeasurable benefits they provide," said DEC Commissioner Basil Seggos. "DEC will continue to investigate the potential threat of elm zigzag sawfly to determine if management actions are needed to protect New York's elms and the variety of wildlife that depend on these trees."

Native to East Asia, the elm zigzag sawfly was discovered in southern Québec in 2020. DEC's Division of Lands and Forests staff began surveying for the pest along the Canadian-U.S. border in 2021. DEC conducted surveys at 12 State-owned properties in proximity to where the sawfly was detected in Canada and that also have a high density of elm trees. Surveyors looked for the distinctive zigzag pattern, for which the insect is named, left behind as the larvae feeds on elm leaves. At this time, sawfly populations appear to be at low levels and causing only minor damage. Additional surveys will be performed throughout the fall to determine the extent of the sawfly's presence and impact in the region.

Once introduced to an area, the elm zigzag sawfly is capable of flying up to 56 miles in a year-further when assisted by wind currents. They can also be transported accidentally on infested nursery stock. The sawfly reproduces asexually with each female laying up to 60 eggs at a time and there are four to six generations a year, allowing these pests to quickly establish themselves in new areas.

DEC encourages the public to report sightings of the elm zigzag sawfly through NY iMapInvasives' online reporting system (leaves DEC website). The Saint Lawrence and Eastern Lake Ontario Partnership in Regional Invasive Species Management (SLELO PRISM) also has opportunities for the public to get involved in their volunteer surveillance network (leaves DEC website).

For more information about the elm zigzag sawfly, visit the Invasive Species Centre website (leaves DEC website). For more information about terrestrial invasive species in New York State and how to help prevent their spread, visit DEC's website.

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