The expansion of the Australian tortoise beetle Trachymela sloanei (Chrysomelidae: Chrysomelinae, Chrysomelini, Paropsina) in Spain: Using human-made shelters for an early detection strategy

1. Invasive alien species are one main driver of biodiversity loss and can cause severe economic costs. Effective management of such species requires early detection of colonising individuals, but this is often hampered by biological or economic constraints. 2. Trachymela sloanei (Blackburn, 1896), an Australian Eucalyptus defoliator beetle, is an invasive alien species that has spread to the Americas, Asia and most recently Europe. 3. We analyse the expansion of T. sloanei in the Iberian Peninsula both at regional and local scales, study its phenology and relative abundance, and explore the use of nest boxes for early detection. 4. The species is spreading steadily, and the area potentially affected has increased dramatically in a few years. Both adults and larvae were observed between June and November, suggesting the occurrence of several overlapping generations. More than 300 individuals were found aggregated behind single nest boxes. 5. We conclude that the installation and monitoring of nest boxes or similar structures (e.g., cork boards) can facilitate early detection of this species.