EN
The karyotypes and structure of the testes were studied in 12 species of Psylloidea belonging to the families Aphalaridae, Psyllidae and Triozidae. Males of ten species, namely Aphalara avicularis Oss., A. rumicicola Klimasz., Camaratoscena speciosa (Flor), Cacopsylla ambiqua Frst., C. peregrina Frst., Bactericera curvatinervis Frst., B. striola Flor., Trioza anthrisci Burckhardt, and T. apicalis Frst. have two seminal follicles per testis, this being the most typical testis structure in Psylloidea. Males of Psylla betulaenanae Oss. and P. ledi Flor. were found to display 4 follicles per testis. Ten species share 2n=24+X0 in males, which is the basic karyotype in Psylloidea as a whole, whereas Bactericera curvatinervis Frst. and B. striola Flor. have 2n=24+neo-XY. In some karyotypes, one B-chromosome was found. Its peculiar behaviour during some stages of the first meiotic division was examined. The karyotype of A. rumicicola was studied after Giemsa C-banding. Using C-band in an autosome pair as the marker of one of the telomeres it was proved that holokinetic chromosomes of psyllids are in fact dikinetic in the first meiotic division.