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.