Molecular phylogeny and population structure of the codling moth (Cydia pomonella) in Central Europe: II. AFLP analysis reflects human-aided local adaptation of a global pest species.

Originally resident in southeastern Europe, the codling moth (Cydia pomonella L.) (Tortricidae) has achieved a nearly global distribution, being one of the most successful pest insect species known today. As shown in our accompanying study, mitochondrial genetic markers suggest a Pleistocenic splitting of Cydia pomonella into two refugial clades which came into secondary contact after de-glaciation. The actual distribution pattern shows, however, that Central European codling moths have experienced a geographic splitting into many strains and locally adapted populations, which is not reflected by their mitochondrial haplotype distribution. We therefore have applied, in addition to mitochondrial markers, an approach with a higher resolution potential at the population level, based on the analysis of amplification fragment length polymorphisms (AFLPs). As shown in the present study, AFLP markers elucidate the genetic structure of codling moth strains and populations from different Central European apple orchard sites. While individual genetic diversity within codling moth strains and populations was small, a high degree of genetic differentiation was observed between the analyzed strains and populations, even at a small geographic scale. One of the main factors contributing to local differentiation may be limited gene flow among adjacent codling moth populations. In addition, microclimatic, ecological, and geographic constraints also may favour the splitting of Cydia pomonella into many local populations. Lastly, codling moths in Central European fruit orchards may experience considerable selective pressure due to pest control activities. As a consequence of all these selective forces, today in Central Europe we see a patchy distribution of many locally adapted codling moth populations, each of them having its own genetic fingerprint. Because of the complete absence of any correlation between insecticide resistance and geographic or genetic distances among populations, AFLP markers do not have a prognostic value for predicting an outbreak of pesticide resistance in the field. By combining mitochondrial genetic data and AFLP analysis it was possible, however, to track the recent evolutionary history of Cydia pomonella on three different time scales: from population splitting in Pleistocene, to interbreeding of mitochondrial haplotypes in Holocene, to human-aided complete intermixing and splitting into many locally adapted populations in very recent times. The case of Cydia pomonella is reminiscent of examples of sympatric speciation and another example of a human-induced globally successful pest species.