The Elm zigzag sawfly (Aproceros leucopoda) is an invasive insect native to Asia, specifically parts of China and Japan. Its common name comes from the zigzag feeding pattern of its larvae. Elm zigzag sawflies feed exclusively on elm trees; elms in a variety of habitats, including arboretums, botanical gardens, roadside trees, urban plantings, and natural woodlands are threatened by the elm zigzag sawfly (2)(3)(4).
Elm zigzag sawfly larvae are light green with a black band on their head with T-shaped markings above the second and third pair of true legs. Adults are black with yellowish-white colored legs and smoky-brown colored wings. Cocoons are loosely-spun and net-like; they can be found attached to leaves or other objects like fence posts(2)(3)(4).
Elm zigzag sawfly was first reported in North America in July of 2020 in Sainte-Martine Quebec. The NYS DEC’s Division of Lands and Forest staff began surveying for the pest along the Canadian- U.S. border in 2021. The pathway of introduction to North America, as well as the amount of time it has been present, is currently unknown (1).
In August of 2022, the elm zigzag sawfly was confirmed for the first time in New York State. Three dead A. leucopoda Takeuchi (Argidae) were collected and confirmed present at Wildland in Brasher Falls in St. Lawrence County. Feeding patterns, characteristic of the elm zigzag sawfly, have also been reported at three locations in St. Lawrence County, the Brasher State Forest, Wilson Hill WMA, and the St. Lawrence State Park. At this time, sawfly populations appear to be at low levels and causing only minor damage. Confirmations were made possible through the survey and diagnostic efforts of the New York State Department of Environmental Conservation Forest Health Diagnostic Lab and USDA APHIS. Continued surveys through these organizations and partners will continue throughout the fall to determine the extent of the sawfly’s presence and impact on the region (1).
Young larvae of the elm zigzag sawfly feed on elm leaves in a distinctive zigzag pattern-hence their name, while older larvae feed more broadly on leaf tissue leaving behind only leaf veins. Although the sawfly has not yet been shown to cause tree mortality, the feeding of the larvae can cause significant defoliation, branch dieback, and crown thinning on infested elm trees. Competition between native sawfly species and native elm foilage-feeding species may become a concern. Infested trees are also more vulnerable to other tree pests and pathogens causing a cascading impact on forest ecology, the economy, and societal values (2)(3)(4).
The elm zigzag sawfly reproduces parthenogenetically, meaning females reproduce without mating. Females can lay up to 60 eggs at a time, with four to six generations a year (2).
The sawfly can be unknowingly spread through the introduction of infested nursery stock. Once introduced, the sawfly can fly up to 56 miles in a year or further when assisted by wind currents(1).
Prevention and early detection are considered to be the best control methods at this time. The NYSDEC encourages the public to report sightings of the elm zigzag sawfly through New York’s invasive species observation database, iMapInvasives.org.
To aid early detection efforts in the St. Lawrence Eastern Lake Ontario region, SLELO PRISM has developed an invasive species Volunteer Surveillance Network (VSN) with partners and community members.