EN
Within the last decades the slug Arion lusitanicus has expanded its range over wide areas of Europe, in most of them it is now a serious pest. Poland has been invaded relatively recently (since the late 1980s). Considering the ecological importance of the slug, very little is known yet about the mechanism of invasion, establishment of new populations and influence on the native fauna and flora. The analysis of nucleotide sequences of mitochondrial cytochrome oxidase subunit 1 gene (cox1) revealed a great inter- and intrapopulation variation in the Polish populations of A. lusitanicus. The differentiation of all the studied Polish populations of A. lusitanicus is 0.2–2.2%, while two analysed Belgian populations are monomorphic and moderately genetically diverse at 0.8%. This indicates a heterogeneous origin of the Polish populations, probably resulting from multiple independent introduction events. The genotype found in the first four Polish populations (S. Poland) suggests that their origin is different from the remaining populations.