Abstract
The population structure of Cacopsylla pruni, the insect vector of ‘Candidatus Phytoplasma prunorum’, was studied from a sampling in 12 localities in western and southern France and in northern Spain. All specimens were collected on Prunus spinosa. More than 300 individuals were genotyped at nine microsatellite loci. Two complementary approaches (Fst, Bayesian clustering) were used to analyse the data and gave congruent results. They show the existence of two strongly differentiated populations (provisionally called A and B). Both populations occurred sympatrically in most sites studied, but the first one was strongly dominant in the Massif Central, and the second one in western France. Despite both populations overlapped over a large geographic area, hybrids seem to be very rare or absent.