EN
The karyotype in two species of Cacopsylla (Homoptera, Psyllidae) from populations was investigated.The males were found to be dimorphic with respect to their sex chromosome constitution and the automosome number.Type A (XO) was described for C sorbi.Type B (XY) was described for C mali and Type C (X1X2Y)for two species in the present work.In Type B and Type C reduction of the autosome number was found.The bahaviour of sex chromosome during meiosis was studied.The scheme was proposed indicationg how the XO type, through X-autosome fusion, gave rise to the neo X1X2Y type.