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Elm zigzag sawfly larvae create characteristic zigzag-shaped damage in elm leaves. Photo Credit: Kelly Oten, NC State University, retrieved from NC State Extension Publications (ncsu.edu).
Elm Zigzag Sawfly
COMMON NAME:
Elm Zigzag SawflySCIENTIFIC NAME:
Aproceros leucopodaORIGIN:
Asia, mainly China and JapanDESCRIPTION:
Elm zigzag sawfly adults are shiny and black with a wasp-like appearance. They have a white patch on the bottom of the thorax and yellow legs. Adult females reproduce asexually and can lay up to 50 eggs at a time. This species can produce 4 – 6 generations each year, but in North America only 2 per year have been observed thus far. Eggs are attached to the leaf margin at the tooth and start out blue green then turn black before hatching. Elm zigzag sawfly larvae begin with a greyish white color and turn green as they mature. The larvae have a dark band on the head and T-shaped markings on the second and third pair of true legs. In the summer, cocoons are found on leaves and have a loosely woven, net-like casing. In the winter, they are solid and buried in leaf litter or soil.HABITAT:
The elm zigzag sawfly feeds and develops on elm trees (Ulmus spp.). This includes many species of elm, both native and non-native, such as winged elm (Ulmus alata), slippery elm (Ulmus rubra), American elm (Ulmus americana), English elm (Ulmus minor 'Atinia'), lacebark elm (Ulmus parvifolia), Siberian elm (Ulmus pumila) and hybrid elms (Ulmus spp.). The elm zigzag sawfly carries out its life cycle on elm trees, including egg production, larval feeding and the pupa stage. This species occupies temperate deciduous forest zones in the mid-latitudes, ranging from 34°S to 59°N, and is found in natural and urban habitats. In winter months, the elm zigzag sawfly can tolerate temperatures as low as -30°C (-22°F).THREAT:
The larvae feed on elm leaves and create a zigzag pattern, and these notches are about 5 – 10 mm into the leaf from the edge. Mature larvae can feed more broadly on leaf tissues and defoliate entire leaves which removes the zigzag shaped damage. Entire leaves can be defoliated with only veins remaining. Currently, elms can recover from periodic defoliation by this pest. But overtime, more persistent defoliation events may cause individual elms to be weakened and susceptible to stressors that could lead to tree decline. The elm zigzag sawfly also competes with native species for food resources.MANAGEMENT:
The elm zigzag sawfly is still in the early detection phase in North America. Please report all sightings of elm zigzag sawfly through iMapInvasives, to help determine the distribution of this species, ahead of any management efforts. Since most elm trees can recover from elm zigzag sawfly defoliation events, control may not be necessary, and research into management options is ongoing. If removal is necessary, small populations can be removed by hand, and larvae can be picked off trees and placed in a bucket of water and soap. Insecticide treatments can be used if the pesticide is labeled for elm zigzag sawfly, and treatment should occur in spring once larvae are present.
SYMPTOMS:
The characteristic zigzag pattern created by larvae in elm leaves is a key sign to identify an early infestation, and larvae can be present on elm trees from May – October. In more advanced infestations, completely defoliated elm leaves with only leaf veins present may be found. Larval cocoons are present underneath eaten elm leaves. The cocoons are found in the summer and have a loosely woven, net-like casing. They can also be found on other objects such as fence posts. Winter cocoons are solid and buried in leaf litter or soil, which makes them difficult to detect.
WNY PRISM PRIORITY:
Data Gap Priority Species
Tier 5 – Survey and Research
ADDITIONAL RESOURCES:
Invasive Species Centre - Elm Zigzag Sawfly
UMass Extension Landscape, Nursery and Urban Forestry Program - Elm Zigzag Sawfly
NYS Prohibited and Regulated Species - Part 575:
PATHWAYS OF INVASION:
The elm zigzag sawfly is native to eastern Asia, which includes Japan, eastern Russia, eastern China and the Korean peninsula. This species was first reported in North America in southern Québec in 2020. It has since been found in the United States including Virginia, Pennsylvania, North Carolina, Maryland, Massachusetts and New York. Elm zigzag sawfly adults are strong fliers and can travel up to 90 km (55 miles) per year, and establish in new elm stands.
REGIONAL DISTRIBUTION:
In the WNY PRISM region, this species has been reported in Allegany and Erie Counties as of January 2024, and has been confirmed in the adjacent Finger Lakes PRISM region. As a data gap priority species, data collection is focused on elm zigzag sawfly presence and distribution in the WNY PRISM region.