Invasion history reconstruction and potential distribution of the ambrosia beetles Euwallacea fornicatus and E. perbrevis (Coleoptera: Scolytinae), two global emerging pests

The global spread of invasive insects poses serious ecological and economic threats to forest ecosystems. Euwallacea fornicatus and E. perbrevis are cryptic ambrosia beetles native to Southeast Asia that have invaded multiple regions worldwide, damaging diverse woody hosts through gallery formation and fungal symbiont inoculation. We compiled confirmed and novel occurrence records to describe their global distributions, reconstruct invasion histories and likely origins using mitochondrial COI phylogenies, and compare their potential distributions through models based on bioclimatic variables. Euwallacea fornicatus has expanded rapidly over the past decades, establishing in North America (2003), Israel (2009), South Africa (2016), South America (2020), Australia (2021), Europe (2022) and Turkey (2024). In contrast, E. perbrevis has an earlier but slower invasion history, with establishments in Hawaii (1918), Central America (1979), Oceania (1982), and North America (2004). Phylogenetic analyses revealed at least six independent introductions for each species. Euwallacea fornicatus primarily originated from native populations in China, Taiwan and Vietnam, whereas E. perbrevis from Indonesia and Thailand, with additional introductions from unknown sources. Secondary spread from invaded regions is also likely. Distribution models indicated distinct climatic niches. Euwallacea fornicatus tolerates broader thermal ranges and drier conditions, enabling establishment from subtropical to temperate regions, whereas E. perbrevis appears restricted to tropical climates. Only 32% of predicted suitable habitat overlapped, indicating low coexistence potential. The broader climatic tolerance and faster recent spread of E. fornicatus highlights a higher invasion risk and greater management challenges. These findings provide key insights to strengthen biosecurity strategies aimed at preventing further spread.