The Elm Zigzag Sawfly is an invasive insect native to Asia that eats the leaves of elm trees. It is monitored by the Canadian Food Inspection Agency (CFIA) after being first discovered in North America in 2020. In 2025 it was found for the first time in Winnipeg. It gets its name from the unique, back-and-forth pattern the larvae leave behind as they chew through the leaves.
https://inspection.canada.ca/en/plant-health/invasive-species/insects/elm-zigzag-sawfly/fact-sheet
CFIA Elm Zigzag Sawfly Reporting Page
More information on this pest can be found on the plant pest cards page. Cards can be printed for your convenience.
How to Identify It
- Zigzag feeding pattern: Larvae carve a distinct "zigzag" trace between the leaf veins.
- Larval stage: Tiny, legless, whitish or green caterpillars up to 8 mm in length.
- Adult stage: Small, shiny black flying insects about 6 to 7 mm long with banded wings.
- Cocoons: Found on the underside of leaves and enclosed in a loose, net-like mesh.
Impact on Trees
- Feeds exclusively on elm tree species.
- Can complete 3 to 4 generations per year, leading to rapid population growth.
- Heavy infestations can cause severe defoliation, stressing the tree.
- While it does not spread Dutch elm disease directly, stressed trees are much more vulnerable to the disease and other pests.
Where It Is Found
- First discovered in Sainte-Martine, Quebec in 2020.
- Has since spread into eastern Ontario, the Greater Toronto Area, and confirmed by CFIA in Winnipeg, Manitoba in 2025.
- Also widespread in parts of the United States.
Prevention and control https://inspection.canada.ca/en/plant-health/invasive-species/insects/elm-zigzag-sawfly/fact-sheet
- Aproceros leucopoda is a strong flier and can disperse locally. It is known to move by human-assisted means via plants for planting and hitch-hiking. Cocoons can be found on twigs and leaves; larvae or pupae may be associated with roots and soil.
- At this time, raising public awareness of the risk of moving infested elm material is essential to help control and limit the spread of A. leucopoda in Canada. Elm trees can be infested with all life stages of the sawfly. Maintaining tree vigour and health, and a diversity of tree species (that is, avoiding monocultures) is one of the best methods to reduce and control infestations of elm zigzag sawfly.
Reporting the Pest
- If you suspect you have spotted the insect or its characteristic leaf damage and to help determine the extent of its distribution, the CFIA is encouraging the public and all stakeholders to submit samples of any suspect pests they observe on elm trees to their local CFIA office. Suspect sightings can also be reported to the CFIA Elm Zigzag Sawfly Reporting Page
- This information will assist in evaluating the extent of the infested area and the threat posed by this pest and will help direct the next steps for Canada.