Elm Zigzag Sawfly – Aproceros leucopoda

Elm Zigzag Sawfly – Aproceros leucopoda Description of Insect: The elm zigzag sawfly (Aproceros leucopoda) has caused significant damage to elm trees across Europe and parts of North America. Adult sawflies are small, typically measuring 6-7 mm in length; with dark black bodies, white legs, and smoky-brown wings. The larvae of Aproceros leucopoda are pale green with black markings on their heads and T-shaped markings on their legs. They are easily recognized by their distinctive feeding patterns, creating a characteristic zigzag pattern on the leaves, which gives the insect its name. The larvae move across the leaves, consuming the tissue between the veins, leaving a skeletonized appearance that ultimately results in defoliation. The larvae can grow up to 11 mm in length before they pupate, weaving a silk cocoon around themselves. The sawfly’s ability to fly up to 90 km per year, coupled with its aggressive feeding behavior, makes it a significant pest to elm trees. Life cycle of Elm Zigzag Sawfly The life cycle of the elm zigzag sawfly consists of four main stages: egg, larva, pupa, and adult. There are no male beetles, and the females reproduce parthenogenetically. Adult female sawflies lay blue-green eggs on the undersides of elm leaves which turn black just before hatching, typically in early spring. The eggs hatch in about 4-8 days, and the larvae begin feeding on the leaves, creating the characteristic zigzag patterns as they chew through the leaf tissue. After approximately 15-18 days, the larvae reach their full size after passing through 6 instars. They spin a silk, net-like case around themselves, attached to the host-plant leaves or on the ground. The pupal stage lasts around 10 days, and adult sawflies emerge to begin the cycle anew. In areas with mild climates, the insect may be active for most of the year, continuously attacking elms. Depending on the environmental conditions, they can produce 2 to 6 generations per year. Damage they cause: The elm zigzag sawfly impacts the trees, as well as the broader ecosystem and human activities dependent on elms.

1. Ecological Impact: Elm trees play a vital role in forest ecosystems, providing shelter, food, and habitat for a variety of wildlife. The feeding activity of the elm zigzag sawfly weakens the trees by stripping them of their leaves. Over time, this leads to stunted growth, premature leaf drop, and, in extreme cases, the death of the tree.

The destruction of these trees by the sawfly can alter the habitat for other species, such as the rare white-letter hairstreak butterfly (Satyrium w-album) and white-spotted pinion moth (Cosmia diffinis). It also competes with the native elm-feeding insects, leading to a decrease in biodiversity in the affected areas.

2. Aesthetic Impact: In residential and recreational settings, elm trees are valued for their shade, beauty, and contribution to the landscape. Infestations of the elm zigzag sawfly reduce the visual appeal of these trees, as the characteristic zigzag feeding patterns and extensive defoliation make them look unhealthy and unsightly. This diminishes the beauty of public parks, streets, and private gardens, resulting in reduced aesthetic quality and land value.

How Elm Zigzag Sawfly got into USA: The elm zigzag sawfly is native to East Asia, where it has been a known pest of elm trees for centuries. It has now spread to other parts of the world, including Europe and North America. However, the exact mode of entry is still unknown. The first confirmed sightings of the elm zigzag sawfly in North America occurred in July of 2020 in Sainte-Martine Quebec. It was then reported in Virginia in 2021, Maryland, Pennsylvania, North Carolina, New York, and Vermont. In 2023, the elm zigzag sawfly was also discovered within Berkshire and Hampden Counties in Massachusetts. Once established in the U.S., the sawfly has spread rapidly, particularly in urban areas where elms are common. Its ability to reproduce quickly has made it a serious pest in these environments.