Expanded geographic range and novel host association of elm zigzag sawfly (Hymenoptera: Argidae) with <i>Zelkova serrata</i> in North America

Abstract The elm zigzag sawfly (EZS), Aproceros leucopoda Takeuchi (Hymenoptera: Argidae), is a rapidly spreading invasive defoliator threatening North American elms (Ulmus spp.). Native to East Asia, EZS has established itself across Europe and Russia and was first detected in North America in 2020. Its parthenogenetic reproduction, high fecundity, and multiple dispersal pathways facilitate rapid range expansion and by 2025, EZS had been documented in 14 U.S. states and 4 Canadian provinces. In North America, human-assisted dispersal via vehicles, wood products, and potentially nursery soil may accelerate its spread beyond natural dispersal distances. This paper documents the first observation of EZS on Japanese zelkova (Zelkova serrata), an ornamental tree within Ulmaceae. In field choice assays, EZS oviposited, fed, and pupated on Z. serrata “Musashino” early in the growing season, although subsequent generations did not utilize the host. This suggests that Z. serrata may serve as an alternate host, likely influenced by earlier leaf-out relative to elm.