Invasion Potential of the Recently Established Woodwasp Sirex obesus (Hymenoptera: Siricidae) Across South American Pine Plantations.

Invasive forest pests are among the greatest threats to global forestry, causing substantial economic losses and disrupting ecosystem dynamics worldwide. The recent detection of the North American woodwasp Sirex obesus (Hymenoptera: Siricidae) in Brazilian pine plantations poses a serious risk to South America's 4.6 million hectares of commercial pine forests. Here, we present the first comprehensive assessment of its invasion potential across the continent, combining species distribution modeling with a multi-factor invasion risk index. Using occurrence records from the species' native range, we modeled climatic suitability across South America and addressed invasion risk by integrating bioclimatic suitability, host distribution, proximity to invaded areas, and wood trade volumes with Brazil. Our model predicts suitable climatic conditions in 48% of South American pine plantation areas, particularly in montane and high-altitude regions along the Andean corridor and central-eastern Brazil. The mean temperature of the driest quarter was the most influential predictor of suitability. The invasion risk index identified southern Brazil, northeastern Argentina, Argentine Patagonia, and central Chile as the regions most vulnerable to the establishment, due to the convergence of extensive pine plantations, favorable climate, and either proximity to infested areas or intense trade connections with Brazil. These findings provide a foundation for targeted surveillance and phytosanitary measures aimed at preventing further spread. Early monitoring in high-risk regions, combined with stricter inspections of wood products, will be critical to avoiding widespread establishment and severe economic impacts across South American forestry.