Insect pest invasions pose a major threat to agriculture, forestry and many natural ecosystems. Thaumastocoris peregrinus is an invasive sap-sucking pest of significant economic importance to Eucalyptus forestry that has recently invaded several countries worldwide. In this study we identify the origin and retrace the invasion history of T. peregrinus. We analysed samples from six locations in Africa, South America and Australia using microsatellites markers and a combination of clustering methods and scenario testing using Approximate Bayesian Clustering. We detected clear genetic substructure differentiating African and South American samples, with representatives of both present in Australia. The Australian population from New South Wales showed substantially higher genetic diversity than the Queensland source, which could indicate that this region could be part of the core range and evolutionary origin of the species. Africa and South America were colonised by independent introductions that occurred more or less concurrently. The study illustrates the impact of the bridgehead effect on global invasions following an outbreak or ‘invasion’ within a city in the native range of the insect.
