GENETIC-STRUCTURE AND DISPERSAL OF PEAR PSYLLA (CACOPSYLLA-PYRI L.) POPULATIONS

The electrophoretic analysis of eight polymorphic enzyme loci in one I talian and 14 French psylla populations showed no significant differen ces between the genotype frequencies and the Hardy-Weinberg equilibriu m. Gene differentiation was low (Fst = 0.0111) and gene flow was high (Nm = 22.3). Populations from western France presented higher gene dif ferentiation than those from eastern France. Separately studying two g enes coding for esterases revealed a high level of structuring. Each l ocus was independent and characterized by a null allele and an express ed allele with the same mobility. The geographical distribution of eac h locus and the existence of confluence zones suggest that the exchang es between sub-populations preferentially occur via the north and the south of the Massif Central. The possible involvement of esterase gene s in resistance to insecticides is discussed in relation with their kn own role of detoxification. (C) Elsevier, Paris.