Inferring the origin of populations introduced from a genetically structured native range by approximate Bayesian computation: case study of the invasive ladybird Harmonia axyridis E. LOMBAERT,* T. GUILLEMAUD,* C. E. THOMAS,† L. J. LAWSON HANDLEY,† J. LI,‡ S. WANG,§ H. PANG,– I. GORYACHEVA,** I. A. ZAKHAROV,** E. JOUSSELIN,†† R. L. POLAND,‡‡ A. MIGEON,†† J. VAN LENTEREN,§§ P. DE CLERCQ,–– N. BERKVENS,–– W. JONES*** and A. ESTOUP†† *INRA, UMR 1301 IBSV (INRA ⁄ Universite ´ de Nice Sophia Antipolis ⁄ CNRS), 400 Route des Chappes, BP 167-06903 Sophia Antipolis Cedex, France, †University Hull, Evolutionary Biology Group, Kingston-Upon-Hull HU6 7RX, N Humberside, UK, ‡College of Environment and Plant Protection, Hainan University, Haikou 520228, China, §Group of Invasive Species Identification and Management, Institute of Zoology, Chinese Academy of Sciences, Beijing, China, –School of Life Sciences, State Key Laboratory of Biocontrol, Sun Yat-Sen University, Guangzhou 510275, China, **Vavilov Institute of General Genetics, Moscow State University, Moscow, Russia, ††INRA, UMR CBGP (INRA, IRD, Cirad, Montpellier SupAgro), Campus International de Baillarguet, CS 30016, F-34988 Montferrier-sur-Lez Cedex, France, ‡‡Clifton College, 32 College Road, Clifton, Bristol BS8 3JH, UK, §§Laboratory of Entomology, Wageningen University, 6708PB Wageningen, The Netherlands, ––Department of Crop Protection, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium, ***Biological Control of Pests Research, National Biological Control Laboratory, ARS, US, DA, PO Box 67, Stoneville, MS, USA Abstract Correct identification of the source population of an invasive species is a prerequisite for testing hypotheses concerning the factors responsible for biological invasions. The native area of invasive species may be large, poorly known and ⁄ or genetically structured. Because the actual source population may not have been sampled, studies based on molecular markers may generate incorrect conclusions about the origin of introduced populations. In this study, we characterized the genetic structure of the invasive ladybird Harmonia axyridis in its native area using various population genetic statistics and methods. We found that native area of H. axyridis most probably consisted of two geographically distinct genetic clusters located in eastern and western Asia. We then performed approximate Bayesian computation (ABC) analyses on controlled simulated microsatellite data sets to evaluate (i) the risk of selecting incorrect introduction scenarios, including admixture between sources, when the populations of the native area are genetically structured and sampling is incomplete and (ii) the ability of ABC analysis to minimize such risks by explicitly including unsampled populations in the scenarios compared. Finally, we performed additional ABC analyses on real microsatellite data sets to retrace the origin of biocontrol and invasive populations of H. axyridis, taking into account the possibility that the structured native area may have been incompletely sampled. We found that the invasive population in eastern North America, which has served as the bridgehead for worldwide invasion by H. axyridis, was probably formed by an admixture between the eastern and western native clusters. This admixture may have facilitated adaptation of the bridgehead population. Keywords: biocontrol, biological invasion, harlequin ladybird, invasive species, microsatellite, source population Received 18 March 2011; revision received 15 September 2011; accepted 16 September 2011 Correspondence: Eric Lombaert, Fax: +33 4 92 38 64 01; E-mail: lombaert@sophia.inra.fr Ó 2011 Blackwell Publishing Ltd Molecular Ecology (2011) doi: 10.1111/j.1365-294X.2011.05322.x