A hitchhiker’s guide to Europe: mapping human-mediated dispersal of the invasive Japanese beetle

Early detection of hitchhiking pests requires the identification of strategic entry points via transport. We propose a framework for achieving this in Europe using the Japanese beetle ( Popillia japonica ) as a case study. Human-mediated dispersal has been responsible for its introduction into several continents over the last century, including Europe where it is listed as a priority pest. Furthermore, interceptions far from the infested area confirm the risk of unintentional transport within continental Europe. Here, we analyse how three modes of transport - air, rail and road - connect the infested area to the rest of Europe. We ranked all European regions from most to least reachable from the infested area. We identified border regions and distant major cities that are readily reachable and observed differences between modes. We propose a composite reachability index combining the three modes, which provides a valuable tool for designing a continental surveillance strategy and prioritising highly reachable regions, as demonstrated by recent interceptions. Significance statement Species can be moved long distances by unintentional human transport. Such events can lead to their introduction into non-native areas where they can cause biological invasions. Using the case study of the Japanese beetle, a hitchhiker invasive insect, we propose a framework for identifying entry points for human-transported pests within Europe. We consider how the European infested area is connected to the rest of the continent by three modes of transport: air, rail and road. We propose a methodology that considers the three modes to identify potential entry points. This framework could assist authorities in designing surveillance strategies to achieve early detection of pests in Europe.