GENETIC CHANGES IN THE POPULATION-STRUCTURE OF THE 2-SPOTTED SPIDER-MITE, TETRANYCHUS-URTICAE KOCH (ACARI, TETRANYCHIDAE), ON VINYL-HOUSE STRAWBERRIES

Two alleles were detected at the phosphoglucoisomerase (PGI) locus of the two-spotted spider mite, Tetranychus urticae KOCH. For clarifying the temporal change in genetic structures of the mite population, we i ntroduced two laboratory-selected strains of the mites which were homo zygous for PGI alleles onto vinyl-house strawberries. The results reve aled that mites initially tended to form breeding colonies on individu al leaflets, but with an increase in their density, they dispersed all over the plants. As a result, the population became genetically homog eneous as a whole.