Abstract
Human transportation networks can provide pathways for invasive species to expand beyond their distribution ranges. The Formosan subterranean termite, Coptotermes formosanus Shiraki, is listed among the world’s worst invasive species and has established invasive populations across continents. Most studies have emphasized transoceanic dispersal and establishment in coastal areas. However, inland expansion at the local and regional scales within the terrestrial landscape has rarely been tracked. Here, we show that expansion of C. formosanus is strongly associated with road transportation infrastructure, particularly the interstate highway system in Alabama, USA. We compiled 40 years of distribution records, primarily reported from the Alabama Cooperative Extension Service and the Alabama Pest Control Association. Since its first detection at the Port of Mobile in 1984, C. formosanus has been recorded in 32 of 67 counties, with an ongoing increase in detections. Our time-to-detection models indicated that climate, urbanization (e.g., road and population density), and the presence of interstate highways were associated with county-level C. formosanus infestation, whereas railway density was not. These results suggest that the expansion of C. formosanus was primarily linked to the interstate highway system, although early spread was often considered associated with railroad infrastructure during the 1980s and 1990s. Our study illustrates a steady northward progression of the species’ established range, highlighting the importance of continued monitoring of inland invasion pathways.