Four decades of inland invasion by Formosan subterranean termite in Alabama: expansion associated with transportation infrastructure

Xing Ping Hu, Nobuaki Mizumoto 

Invasive termites pose ecological and economic concerns as both cellulose-destroying pests and ecosystem engineers. 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 their transoceanic international dispersal and establishment in the 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, human population density, and the presence of interstate highways were associated with county-level C. formosanus infestation, whereas small roads or railway density were not. These results suggest that the spread has shifted from railroad-related infrastructure in the 80s and 90s, after incubation around the city with railroad stations. Our study illustrates a steady northward progression of the species’ established range, highlighting the importance of continued monitoring of inland invasion pathways.