The invasive ambrosia beetle Euwallacea fornicatus (Eichhoff, 1868) poses a significant threat to forests sensu latu in South America. Uruguay marked the third regional record since 2022, following infestations in Brazil and Argentina. The pest’s distribution now spans ~ 3,500 km of coastline, highlighting its adaptability to diverse climates and the vulnerability of urban ecosystems. Currently, two infestations started in Uruguay in two foci distant 500 km of each other: Rivera, a northern city bordering with Brazil and an established beetle population in Montevideo, the capital and a port city in the southern region of the country. The infestation in Montevideo initially mirrors those in the city of Buenos Aires, Argentina, with low attack densities (< 30 attacks/tree) concentrated at lower trunk heights (< 4 m). The key host species include Acer negundo L., Casuarina cunninghamiana Miq. and Platanus × acerifolia (Aiton) Willd., indicating an affinity for common urban trees in the Southern Cone. This pest is known to attack 602 plant species. However, our host plant survey recorded fourteen new host plant species, with nine new breeding hosts. While tree mortality is not yet evident, gallery excavation and symbiotic fungal activity threaten tree health and tend to escalate management costs. Molecular analyses confirm the presence of a single haplotype within E. fornicatus species, which is phylogenetically close to Argentine, Brazilian, Chinese and European populations. The rapid spread across Uruguay along with the increasing number of hosts with breeding potential, both exotic and native in Argentina and Uruguay, highlights the significant invasion threat this species poses for South America. It is crucial to implement coordinated supranational management strategies without delay. Considering the size of the populations, they should include eradication efforts using mechanical and chemical means, followed by continuous monitoring to prevent re-emergence or re-introduction of propagules from neighbouring countries.
