The elm zigzag sawfly (Aproceros leucopoda) is an invasive species that defoliates trees in the elm genus (Ulmus spp.) in the larvae stage. It was detected first in North America in Canada (2020), and was first found in North Carolina in 2022. It originates from eastern Asia. It has recently been found for the first time in Buncombe County.

Elm zigzag sawfly can be found in either the larval stage, pupae stage or adult stage. Eggs are laid on elm leaf serrations in early spring and, as the larvae hatch (usually within 8 days), they feed on the leaves in a zigzag pattern defoliating the elm tree quickly.

Larvae is gray-white when they first emerge from eggs and mature to be green with a characteristic black band on their head and black t-shaped markings on their second and third set of legs.

They then pupate in cocoons that are loosely-spun net-like cocoons on the back of leaves, tree trunks, or nearby objects in summer. They can also overwinter in solid-walled cocoons in leaf litter on the ground. The elm zigzag sawfly can travel long distances via human assistance by attaching their cocoons to vehicles or other objects, as well as fly long distances. Be aware and on the lookout if you are entering areas with known infestations.

After ten days on average during the summer months, winged adults emerge from the cocoon and start the process all over again laying eggs on the leaf margins of elm trees. Adults are small (7-8mm long) with a white patch on the underside of the thorax, dark brown “upper lip”, and have yellow-white legs.

In NC, 4 generations have been observed within a year, but this varies and research is ongoing. Interestingly, elm zigzag sawflies reproduce using parthenogenesis meaning that females lay eggs without ever having to mate (no male elm zigzag sawfly has ever been found).

If you notice elm defoliation and suspect elm zigzag sawfly could be the culprit:

1. Note the location
2. Try to photograph the insect and the leaves that have been eaten upon
3. Contact your local NCFS county ranger, your local cooperative extension office, or utilize this reporting form to notify where the suspected insect has been found.

This is a relatively new pest but we do know that most trees can ultimately recover from defoliation due to elm zigzag sawfly. In situations where specimens are defoliated year after year, tree decline could ultimately occur if treatment is not administered. Research is ongoing into management of this insect, however systemic insecticide products dinotefuran and imidacloprid have both been found to treat infestations of this insect in other areas. Always follow pesticide label instructions and be mindful of application timing, safe handling practices, and appropriate dosage. Stay up to date on the latest research as it is ongoing into what the best treatment plan is. If you have questions, reach out to your local county cooperative extension office.

Elm Zigzag Sawfly Factsheet- NCSU Extension

NCFS County Offices

Elm Zigzag Sawfly Reporting Form