11 Abstract Native to Asia, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is 12 considered an invasive alien ladybird in Europe and North America, where it was widely 13 introduced as a biological control agent of aphids and coccids. In Europe, H. axyridis was 14 sold by various biological control companies from 1995 in France, Belgium and the 15 Netherlands, and was also intentionally released in at least nine other countries. It has 16 spread very rapidly, particularly since 2002, and is now regarded as established in thirteen 17 European countries. The established range extends from Denmark in the north to southern

11 Abstract Native to Asia, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is 12 considered an invasive alien ladybird in Europe and North America, where it was widely 13 introduced as a biological control agent of aphids and coccids. In Europe, H. axyridis was 14 sold by various biological control companies from 1995 in France, Belgium and the 15 Netherlands, and was also intentionally released in at least nine other countries. It has 16 spread very rapidly, particularly since 2002, and is now regarded as established in thirteen 17 European countries. The established range extends from Denmark in the north to southern

Understanding the evolutionary histories of invasive species is critical to adopt appropriate management strategies, but this process can be exceedingly complex to unravel. As illustrated in this study of the worldwide invasion of the woodwasp Sirex noctilio, population genetic analyses using coalescent-based scenario testing together with Bayesian clustering and historical records provide opportunities to address this problem. The pest spread from its native Eurasian range to the Southern Hemisphere in the 1900s and recently to Northern America, where it poses economic and potentially ecological threats to planted and native Pinus spp. To investigate the origins and pathways of invasion, samples from five continents were analysed using microsatellite and sequence data. The results of clustering analysis and scenario testing suggest that the invasion history is much more complex than previously believed, with most of the populations being admixtures resulting from independent introductions from Europe and subsequent spread among the invaded areas. Clustering analyses revealed two major source gene pools, one of which the scenario testing suggests is an as yet unsampled source. Results also shed light on the microevolutionary processes occurring during introductions, and showed that only few specimens gave rise to some of the populations. Analyses of microsatellites using clustering and scenario testing considered against historical data drastically altered our understanding of the invasion history of S. noctilio and will have important implications for the strategies employed to fight its spread. This study illustrates the value of combining clustering and ABC methods in a comprehensive framework to dissect the complex patterns of spread of global invaders.