Parthenogenesis is common among invasive pest species,with many parthenogenetic species also showing polyploidy.Parthenogenetic polyploid species often have multiple hybrid origins and the potential to rapidly spread over vast geographical areas.In this study,we examine pattes of mitochondrial and microsatellite variation in a widespread triploid parthenogenetic chironomid pest species,Paratanytarsus grimmii.Based on samples from five countries,including Australia,England,Germany,Japan,and Canada,we found extremely low mitochondrial diversity (＜ 0.14％),with most individuals sharing a common and widespread haplotype.In contrast,microsatellite diversity revealed 41 clonal variants,which were regionally endemic.These findings suggest a single invasive mateal lineage of P.grimmii is likely to have recently spread over a broad geographical range.High levels of genotypic endemism suggest P.grimmii populations have remained relatively isolated after an initial spread,with little ongoing migration.This,in part,can be attributed to rapid genetic differentiation via mutations of common clonal genotypes after P.grimmii spread,but multiple polyploidization and subsequent founder events are also likely to be contributing factors.