Nechayeva, G.A., Davis, C.J., & Nokkala, S. 2004 [New data on the karyotype of Pseudococcus viburni (Sign.) (Homoptera, Coccinea).]. Entomologicheskoe Obozrenye 83(1): 23-31.
Notes: Karyotype of P. viburni has been studied for the first time using different chromosome staining techniques. The pattern of differential staining of chromosomes and their behaviour in the early embryogenesis of males and females have been analysed. Nucleolar-organizing chromosomes and nucleolar-organizing regions (NORs) have been revealed in the karyotype by the Ag-NOR technique. Content and distribution of constitutive heterochromatin (C-heterochromatin) in chromosomes have been determined by the C-banding technique. Molecular composition of C-heterochromatin has been determined using DNA-specific fluorochromes DAPI and CMA3. P. viburni displays 2n=10, a karyotype symmetrical in structure, holokinetic chromosomes; the largest pair of chromosomes bears a "secondary" constriction situated proximally in every homologue. Sex determining mechanism is the haplo-diploidy of the "lecanoid" type. In the early embryogenesis of males, one haploid chromosome set is heterochromatinized and is genetically inactivated, except for the ribosome gene sites (NORs). Chromosomes of the largest pair are nucleolar-organizing, NORs being situated in the area of the secondary constriction. In every chromosome there are large telomeric and dot interstitial C-heterochromatin blocks. C-blocks consist of both A-T- and G-C-rich DNA clusters. NOR sites in the nucleolar-organizing chromosomes are exceptional showing G-C-rich DNA clusters, but no A-T-rich clusters. In the population examined, B-chromosomes have been found. Their number in cells of the same individual varies from 0 to 2 and 1 B chromosome occurs most frequently. B-chromosomes are large, positively heteropycnotic and consist completely of C-heterochromatin.