Globalization of trade and travel is increasingly responsible for the accidental transport of non-native species worldwide. Insects are the most numerous and diverse group of invasive animals, and have widespread impacts on biodiversity, agriculture and human health. Previous studies modelling the spread of invasive insects have largely used general measures of trade such as GDP as a proxy for propagule pressure. However, general trade flows can be very different from trade in specific commodities, and consequently may fail to explain the dispersal of species exclusively transported with a few commodities. This study aims to improve our understanding of introduction pathways for invasive insects by testing i) if the transport of individual species is associated with specific commodities and ii) if different insect families share commodity profiles.
Using border interception records from USA, New Zealand, Australia, Korea and Japan we analysed commodities linked to dispersal of non-native insects from 1960 onwards. We classified the commodities insects are intercepted on using an internationally standardized system for trade products, with hierarchical levels analogous to taxonomic classification. Patterns of commodity diversity among insect species were analyzed using a Double Principle Component Coordinate Analysis, accounting for the hierarchical classification of both species and commodities.
Results/Conclusions
We identified broad groups of commodities transporting the most important families of invasive insects, e.g. ants were largely associated with fruit and live plants. However, as many species were highly commodity specific, this level of precision is not sufficient to predict the spread of individual species. Technomyrmex albipes for example was almost exclusively intercepted on orchids, and Camponotus linnaei was only intercepted on bananas. These patterns are likely to be applicable for other groups of insects, and have implications both for further research and the development of management protocols and policy. Insects are almost exclusively introduced unintentionally, as contaminants of traded commodities or as stowaways attached to a transport vector. If many insect species are exclusively transported with specific commodities, it may explain why some previous studies have found no link between patterns of insect invasions and general trade metrics such as GDP. Our results suggest that modeling the spread of specific insect species will require a precise understanding of the associated transport vectors, rather than simply including a general measure of trade as a proxy for human-mediated dispersal.