Technical Abstract: First detected in Europe in 1992, the western corn rootworm (Diabrotica virgifera virgifera), the most destructive pest of maize in the USA, is now present in several European countries. To discriminate between introduction scenarios, genetic variation of European and American western corn rootworm populations was analyzed at eight microsatellite loci, using an Approximate Bayesian Computation (ABC) framework relying on computer simulations. For each European outbreak, our ABC method allowed quantitative comparison of different introduction scenarios that differ by putative source populations: the USA or one of the other European populations. Our results indicate that three out of the five analyzed western European outbreaks did not originate from the Central Europe spreading area, but from the USA. Moreover, these introductions were independent from each other and from the initial European introduction in Central Europe.