They are among us: the European invasion of the alien brown marmorated stinkbugs Halyomorpha halys (Heteroptera, Pentatomidae)

The brown marmorated stinkbug (BMSB), Halyomorpha halys is an invasive alien species native to eastern Asia. Its presence outside the original area of distribution has been recorded for the first time in North America (Canada and U.S.A.) and, more recently, in Europe (Switzerland, France, Hungary, Romania, Austria, Serbia and Italy), where H. halys is spreading rapidly. Other than being a household pest all over its introduced range, this stinkbug is causing great economic losses in the U.S.A and Italian orchards/crops due to its highly polyphagous nature and bivoltinism. Tracing back the pattern of introduction and monitoring the spread of BMSB in the European territory will be useful to implement better pest control strategies. The present study aimed to identify the potential pathways of entry of H. halys in Europe by detecting the genetic diversity of specimens collected all over Italy, and in Switzerland, Romania and Greece. The analyses of 1,175 bp of mitochondrial DNA cytochrome c oxidase I and II genes (cox1 and cox2) of over 200 specimens led to the identification of 12 haplotypes never observed before (10 for cox1 and 2 for cox2). Present data indicate a higher haplotype diversity of European specimens compared with the American ones; instead, the diversity is lower with regard to the Asian samples, except for the cox2 marker. A clear-cut difference in haplotype distribution was found between North and South Europe: Switzerland and France share a similar haplotype pattern, whereas Italian, Hungarian, Romanian and Greek samples are more similar, with the Italian and Greek specimens showing the higher genetic diversity. In Italy, genetic diversity for both markers is higher in Piedmont, Lombardy and Veneto, while in the remaining regions of Northern Italy in which the species is spread, it is fairly low. Haplotype similarity with both Chinese and Korean samples led to hypothesize that the introduction of H. halys in Europe, and in Italy in particular, has occurred by means of multiple events from Asia and that the BMSB is currently expanding its range in the European continent.