Why so many Hemiptera invasions?

Aim The Hemiptera is the fifth-largest insect order but among non-native insect species is approximately tied with the Coleoptera as the most species-rich insect order (Hemiptera comprise 20% more species than in world fauna). This over-representation may result from high propagule pressure or from high species invasiveness. Here, we assess the reasons for over-representation in this group by analysing geographical, temporal and taxonomic variation in numbers of historical invasions. Location Global. Method We assembled lists of historical Hemiptera invasions in 12 world regions, countries or islands (Australia, Chile, Europe, New Zealand, North America, South Africa, South Korea, Japan and the Galapagos, Hawaiian, Okinawa and Ogasawara Islands) and border interception data from nine countries (Australia, Canada, European Union, United Kingdom, Hawaii, Japan, New Zealand, South Korea, USA mainland and South Africa). Using these data, we identified hemipteran superfamilies that are historically over-represented among established non-native species, and superfamilies that are over-represented among arrivals (proxied by interceptions). We also compared temporal patterns of establishments among hemipteran suborders and among regions. Results Across all regions, patterns of over- and under-representation were similar. The Aphidoidea, Coccoidea, Aleyrodoidea, Cimicoidea and Phylloxeroida were over-represented among non-native species. These same superfamilies were not consistently over-represented among intercepted species indicating that propagule pressure does not completely explain the tendency of some Hemiptera to be over-represented among invasions. Asexual reproduction is common in most over-represented superfamilies and this trait may be key to explaining high invasion success in these superfamilies. Conclusions We conclude that both propagule pressure and species invasiveness are drivers of high invasion success in the Sternorrhyncha suborder (aphids, scales, whiteflies) and this group plays a major role in the exceptional invasion success of Hemiptera in general. The high historical rates of invasion by Sternorrhyncha species provide justification for biosecurity measure focusing on exclusion of this group.