Got Nature? Blog

Purdue Landscape Report: The elm zigzag sawfly (EZS), Aproceros leucopoda, is a non-native insect recently detected in several midwestern states. Originally from eastern Asia, this insect is rarely considered a problem in its native range, having several natural enemies and environmental factors able to keep it in check.

Figure 1. Elm zigzag sawfly adult, Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org

However, when in new landscapes, aspects of this insect’s life cycle enhance its ability to spread across new habitats and do significant damage to its host plant, the elm tree. EZS was first detected outside of its native range in Europe in 2003. Then, in 2020, it was found in North America for the first time in Quebec. It has since been detected in several states in the US, spreading first through the Northeast before entering the Midwest. It has not yet been detected in Indiana, but has been in the surrounding area.

Elm zigzag sawfly is a member of the insect order Hymenoptera, which includes bees, ants, and wasps. More specifically, sawflies belong to a suborder known as Symphyta, whose members are noted for a broad-waisted appearance and a saw-shaped ovipositor. Sawflies are a fairly common group of insects, though observers will often overlook them or confuse them for other insects. Adult EZS are generally small, darkly-colored insects that are easy to write off as ‘just another black bug’ you see around the garden or yard (Fig. 1).

Figure 2. Elm zigzag sawfly larva feeding, Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org

They resemble wasps, but possess a broad waist with no narrowing of space between the thorax and abdomen, and they lack a stinger. EZS larvae closely resemble caterpillars in both form and feeding habits, with pale green coloration, a black stripe that runs down the length of the body, and dark T-shaped markings on the legs (Fig. 2). The larvae, like moth and butterfly caterpillars, will also possess six pairs of fleshy prolegs that are lost upon reaching maturity. While the larvae bear chewing mouthparts to consume the leaf material of many kinds of plants, the adults are nectar and pollen-feeding. It should be noted that EZS larvae chew zigzag patterns into elm leaves, thus the common name of the insect. Like bees and wasps, sawflies also possess wings, but are typically lazy fliers, choosing to fly only during warm, sunnier periods of the day.

View the rest of the article here: A New Threat to Elms in North America

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Resources:
Intro to Trees of Indiana: American Elm, Got Nature? Blog, Purdue Extension – FNR
Intro to Trees of Indiana: Slippery Elm, Got Nature? Blog, Purdue Extension – FNR
ID That Tree, Playlist, Red Elm, Siberian Elm, Winged Elm, Purdue Extension – Forestry and Natural Resources (FNR) YouTube Channel
ID That Tree, Playlist, Purdue Extension – FNR YouTube Channel
Invasive Species Playlist, Playlist, Purdue Extension – FNR YouTube Channel
A Woodland Management Moment, Playlist, Purdue Extension – FNR YouTube Channel
Woodland Stewardship for Landowners, Playlist, Purdue Extension – FNR YouTube Channel
Indiana Department of Natural Resources: Invasive Species
Indiana Invasive Species Council
Cooperative Invasive Species Management Area (CISMA)
Report Invasive, Purdue Extension
Episode 11 – Exploring the challenges of Invasive Species, Habitat University-Natural Resource University
What are invasive species and why should I care?, Got Nature? Blog, Purdue Extension – FNR
Native Trees of the Midwest, The Education Store, Purdue Extension’s resource center
Investing in Indiana Woodlands, The Education Store
Forest Improvement Handbook, The Education Store

Bob Bruner, Exotic Forest Pest Educator
Purdue Entomology