Résumé
The aphid relative Daktulosphaira vitifoliae (Fitch) (Homoptera : Phylloxeridae) feeds on the leaves and roots of grapevine (Vitis spp.). The insect was introduced into France from North America around 140 years ago and caused severe damage until control of the root-infesting form was initiated by grafting European cultivars onto resistant rootstocks. The objective of our research was to analyze both the variation in pathogenicity and the genetic diversity of the insect in southern France. Twenty samples of phylloxera were collected from leaf galls throughout the region. Their aggressiveness was monitored by measuring the reduction in root dry mass of artificially inoculated potted plants. One trial was performed with three rootstocks (41B, 3309C and 140R) and another with the highly susceptible Vitis vinifera cv. Carignan. No evidence for preference was shown, but aggressiveness varied widely among phylloxera samples, especially in the Carignan trial. Genetic diversity was assessed using 30 Random Amplified Polymorphic DNA (RAPD) markers obtained with 15 primers. Wide diversity was found and all samples corresponded to distinct RAPD phenotypes. The genetic structure of phylloxera population in Southern France was not showed to be influenced either by the location or by the host.