Comparison of insect invasions in North America, Japan and their Islands

Among the various animal taxa that are have established outside their native ranges, invasions by insect species are the most numerous worldwide. In order to better understand the characteristics of insect species that make them more invasion prone, the characteristics of habitats that make them more susceptible to invasions and to understand the pathways that facilitate invasions, we compared the compositions of the native and non-native insect communities among five Pacific regions: North America, the Hawaiian Islands, mainland Japan, Ogasawara and Okinawa Islands. These regions comprise both island and mainland habitats and have historically been subjected to varying activities affecting insect movement. Among the five regions, the oceanic islands, Hawaii and Ogasawara, appear to be the most prone to invasions. Specific insect orders such as the Blattodea, Siphonaptera, Thysanoptera and Hemiptera are disproportionally represented in the non-native insect fauna compared to the native fauna in all regions. A large fraction of the non-native insect species in North America (9.4 %) and Hawaii (13.2 %) were introduced intentionally, as part of biological control programs, which were historically pursued more vigorously in those regions than in Japan. Dominance by individual insect orders within invaded communities can be explained by the historical importance of invasion pathways, some of which were likely similar among regions (e.g., movement on live plants), while other pathways appear more region specific. Translocation of insect species among world regions appears to be affected by climatic similarity, host plant similarity and propagule pressure, though these effects are often confounded.