Reproductive mode of grape phylloxera (Daktulosphaira vitifoliae, Homoptera: Phylloxeridae) in Europe: molecular evidence for predominantly asexual populations and a lack of gene flow between them.

The genetic structure of European grape phylloxera populations, Daktulosphaira vitifoliae (Homoptera: Phylloxeridae), was analyzed using 6 polymorphic microsatellite markers. Genetic diversity data of 6 populations originating from northern and southern European viticultural regions was assessed for geographic differences, and the structure of 2 additional populations was examined in more detail, focusing on specific host plant and habitat characteristics. To test for "signatures" of clonal reproduction, different population genetic measures were applied to the data obtained from these populations. A total of 195 multilocus genotypes were detected in 360 individuals tested. Significant deviations from Hardy-Weinberg equilibrium, negative FIS values (from -0.148 to -0.658 per population), and the presence of multicopy genotypes revealed that the current major reproductive mode at each of the locations tested was asexual. The high genotypic diversity detected within and among populations, however, together with the occurrence of unique D. vitifoliae genotypes, indicates sexual recombination events took place, probably prior to the multiple introductions into Europe. The absence of overlapping genotypes between the sampling sites suggests low migration rates among the populations studied and implies that the main mode of insect dispersal is through infested plant material carried by human agency. The specific features of European D. vitifoliae habitats are illustrated to discuss the role of habitat and life cycle in the genetic structure of this globally important pest aphid species.