Mature larvae are green, 10 to 11 mm long, head capsule 1.4 to 1.5 mm wide and green with one black band at each side. On hatching, larvae are grayish-white, 1.8 mm long, 0.3 mm wide. They are 0.8 to 1.0 mm long and 0.4 to 0.5 mm wide and are difficult to detect. Identification EggĮggs are tiny and blue-green, turning black before hatching, and are attached to the leaf margin right at the tip of each tooth. Upper crown die-back of branches is indicative of severe defoliation activity by the zigzag elm sawfly. As the larva matures, it turns around and eats toward the leaf edge, obliterating the zig-zag appearance, but leaves the leaf mid-rib intact. Brown leaves with branch mortality in the upper crown of host trees occur at high population levels.Įlm leaf eating with conspicuous zigzag cut channels from the leaf edge inwards is characteristic of early-stage feeding damage caused by Aproceros leucopoda (figure 4). Detection and identification Symptomsįlagging of upper crown branches coupled with severe leaf eating is characteristic of pest activity by Aproceros leucopoda. Trees in isolation (roadsides, fields) seem to be more frequently attacked and harmed. New growth after complete defoliation can be attacked by the next generation, leading to general weakening of the tree. Heavy attacks may induce crown die-back through severe defoliation of branches. The elm zigzag sawfly is a leaf eater causing defoliation that can attack elm hosts at any age or stage of development. This adaptive life strategy allows this insect to rapidly build up populations and successfully overwinter each year. The denser cocoons generally overwinter in the duff layer on the ground and adults emerge the following year. Two types of cocoons, light summer net-like cocoons and dense cocoons, are produced throughout the spring and summer (figure 3). Pupation occurs in 2 to 3 days with adults emerging 4 to 7 days later. The pre-pupal or eonymph stage loosely spins a cocoon and attaches itself to some structure such as the underside of the leaf, a twig or shoot, or anything underneath the tree. Larvae develop through 6 larval instars which are usually completed in 15 to 18 days. As larvae grow and develop they completely consume the entire leaf, except for the leaf mid-rib (figure 2). After 4 to 8 days larvae hatch and feed on leaves leaving a typical zigzag feeding channel on the leaf underside (figure 1). Eggs are laid singly into the serrated leaf margin. Females commence egg laying immediately after emergence and lay about 7 to 49 eggs. Adult females are present during the summer months and they live from 1 to 6 days. One generation can develop in about 24 to 29 days.Īproceros leucopoda is parthenogenetic and no males are known to exist. Larvae are usually found from late May to mid-October. Adults generally occur from mid-April to mid-September. This sawfly is an outbreak species as it is parthenogenetic and can produce up to 6 generations per year. The life cycle of Aproceros leucopoda is multivoltine (multiple generations that span one year) with an overwintering pupal stage. It is the only known established area in North America. The source of this introduction is unknown.

North America: The elm zigzag sawfly was confirmed in the province of Québec, in August 2020. DistributionĪsia: It is distributed throughout various parts of Asia, specifically parts of China (Gansu) and Japan (Hokkaido Honshu).Įurope: It has been introduced and spreading in Europe. Urban environments provide suitable hosts of all ages. It is generally found in temperate deciduous forests where it can successfully overwinter. HostsĪproceros leucopoda feeds exclusively on elms ( Ulmus spp.). In August 2020, the Canadian Food Inspection Agency (CFIA) confirmed the presence of the elm zigzag sawfly in Québec. The elm zigzag sawfly was reported for the first time in North America in Sainte-Martine, Québec, in July 2020 by a citizen scientist who reported it on iNaturalist.ca. The zigzag sawfly is well adapted to overwinter in temperate deciduous forests. Feeding larvae are usually present in each of the growing season months (May to September).

It is an invasive species that reproduces parthenogenetically and can produce up to 4 generations per year in temperate regions of the world. The zigzag elm sawfly, Aproceros leucopoda Takeuchi, 1939, is an insect pest that feeds on elms ( Ulmus spp.) during its larval stages and can cause severe defoliation damage. Aproceros leucopoda Takeuchi – (Elm zigzag sawfly) – Fact sheet Background

Zigzag plant information