Bionomics of the Non-Native Elm Defoliator Aproceros leucopoda (Hymenoptera, Argidae) in North-Eastern Italy
Department of Agricultural, Food, Environmental and Animal Sciences (DI4A), University of Udine, Via delle Scienze 206, 31000 Udine, Italy
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Insects 2026, 17(4), 390; https://doi.org/10.3390/insects17040390
Submission received: 26 February 2026
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Revised: 27 March 2026
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Accepted: 1 April 2026
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Published: 3 April 2026
(This article belongs to the Special Issue Hymenoptera in Agroecosystems: Functions, Risks, and Management)
Simple Summary
The East Asian zigzag elm sawfly is a pest that feeds on elm trees and can cause severe defoliation in urban areas and mixed forest plantations. Over the past 20 years, it has spread across Europe and has recently been detected in North America, raising concerns about the health of elms. In north-eastern Italy, this invasive species was first detected in 2009. Its life history in newly invaded areas is not fully known. This study investigated the phenology and the number of generations per year the sawfly develops over the vegetative season in north-eastern Italy. Weekly field sampling over two years (2012–2013) showed five peaks of adult captures, suggesting five generations. However, in 2013, no eggs were found for the final generation, probably due to very high summer temperatures and drought that stressed the elm trees. From 2013 to today, a progressive decline in A. leucopoda populations has been recorded. Several natural enemies were observed during the study. These findings can help predict future outbreaks and support better management of elm trees in cities and mixed forest plantations.
Abstract
Aproceros leucopoda (Hymenoptera: Argidae) is an East-Asian pest of Ulmus spp. that has spread across Europe since the 2000s and, more recently, to North America, causing repeated defoliation of host plants. Laboratory studies have suggested four or five generations per year in Hungary; however, in the field, their number ranges from one to six. In 2012 and 2013, the bionomics of this invasive pest were studied in north-eastern Italy through weekly samplings from April to October, with data related to accumulated degree days (DDs). Although adult captures exhibited five peaks in both years, only in 2012 were eggs of the fifth and last generation of the season. Their apparent absence in 2013 might be due to elm water stress or temperatures much higher than optimal (30 vs. 19.5 °C). From 2013 to today, a progressive decline in A. leucopoda populations has been recorded. The possible reasons for the gradual decline in the sawfly population recorded in the subsequent years are discussed. Several natural enemies were observed. This study can contribute to a better understanding of A. leucopoda population dynamics in newly colonised areas, including the risk to wood production in mixed deciduous plantations if defoliation occurs over many consecutive years.
