Elm Zigzag Sawfly

What is Elm Zigzag Sawfly?

(Aproceros leucopoda)

Elm Zigzag Sawfly (EZS) is an invasive forest insect native to East Asia. EZS is a new pest to North America (first reported in 2020 in Quebec, Canada) and to Vermont (first reported and confirmed in Swanton, VT in August 2023). EZS targets and feeds on elm trees exclusively.

Since it is a relatively new invasive species to the US, best management practices are still being determined. These insects are strong fliers which increases their spreading potential. EZS can travel up to 90 km per year. That’s nearly 56 miles in a single year!

What to look for? 

Elm zigzag sawfly have four physical forms through their lifecycle:

• Egg: blue green in color and turns black right before hatching. The eggs are found attached to the leaf margin at the tip of the leaf tooth.
• Larva: initially grayish white in color. Mature larvae are green with black spots near breathing openings and have one triangular black spot on their upper back near the 3rd body segment
• Pupa: encapsulated in cocoons that are attached to undersides of leaves, branches, or shoots. Appearance varies depending on the time of year they’re observed.
• Adult fly: black with yellow-white legs and smoky-brown wings.

EZS larvae produce a characteristic “zigzag” pattern that can be observed in elm leaves after feeding. As the larvae age, they feed more broadly on the leaves, leaving only thick leaf veins, and eventually resulting in complete defoliation of a tree.

Usually, a defoliated tree can recover from a defoliation event. Repeated mass defoliation, however, may cause the tree to become weakened or stressed, which can put them at risk of other pests, disease, or, sometimes, tree death.