Climatic suitability and invasion risk of the elm zigzag sawfly in North America

The elm zigzag sawfly, Aproceros leucopoda (Hymenoptera), native to eastern Asia, is among the most concerning potential pests for elm trees ( Ulmus spp.); elms form an important component in many North Temperate forests. This sawfly species invaded Europe in 2003 and spread rapidly across much of that continent. In 2020, it was recorded in North America, and it has since become established in several parts of the eastern United States and Canada. Sawfly infestations can cause severe elm tree defoliation, branch die-back that weakens tree health, and potentially tree mortality. Sawfly invasions have the potential to further exacerbate elm decline, especially in conjunction with other pressures, including Dutch elm disease ( Ophiostoma ulmi ). We used rigorous approaches from distributional ecology to explore climatic suitability for A. leocopoda across North America, considering various sources of uncertainty in the data. We found that, without control, the elm zigzag sawfly could establish populations across eastern Canada, much of the central-eastern and northeastern United States, as well as in the Pacific Northwest. More southern areas of North America were not climatically suitable for this species. Predicted suitable areas for the sawfly overlap broadly with elm distributions, highlighting the need to control this invasion to mitigate potential economic and environmental impacts.