Phylogeography and Wolbachia Infections Reveal Postglacial Recolonization Routes of the Parthenogenetic Plant Louse Cacopsylla myrtilli (W. Wagner 1947), (Hemiptera, Psylloidea)

To reveal the phylogeographic pattern of the parthenogenetic psyllid Cacopsylla myrtilli (W. Wagner 1947) (Hemiptera, Psylloidea), we sequenced a 638 bp fragment of the mitochondrial COI gene from 962 individuals. These insects originated from 46 sampling sites, which cover a significant part of the northern Palearctic distribution range of the species. The sequence data revealed 40 haplotypes, with three main (H1, H2, and H3) and 37 derived ones. The main haplotypes H1 or H2 or both were present at all sampling sites. The star-like shape of the haplotype networks indicated recent population expansion. In most cases, the derived haplotypes were specific for each country, suggesting that the main haplotypes H1 and H2 are of refugial origin, and the derived haplotypes have emerged after the postglacial recolonization process. Based on the haplotype sequences, we suggest H3 to represent the ancestral haplotype from which H1 and H2 have evolved. We suggest that the main haplotype H3 together with its derived haplotypes represents bisexual C. myrtilli, which shows a limited distribution on both sides of the border between Finland and Russia in northern Fennoscandia. The genetic diversity was the highest in Sjoa in southern Norway and also high in the White Sea region in northwest Russia. Higher diversity in Sjoa was attributed to both earlier recolonizations compared to that of the White Sea region and the absence of Wolbachia infection. We suggest that these sites were colonized from different Pleistocene refugia, i.e., from western and eastern refugia, respectively. From the White Sea region, recolonization continued eastwards to Ural Mountains and westwards to Finland and further north to Kola Peninsula. From northern Finland, recolonization continued to Finnmark, Norway, and further to Sweden and finally reached a secondary contact zone with colonizers from Norway in Central Sweden. The Caucasus and Siberian/Manchurian refugial regions have played an important role in the origin of C. myrtilli populations in Siberia and the Russian Far East.