Cytogenetic Analysis of 3 Populations of Diabrotica speciosa (Chrysomelidae, Galerucinae): Constitutive Heterochromatin and Nucleolus Organizer Regions

Abstract

The genus Diabrotica is characterized by having a great uniformity of karyotype in respect to the chromosome number and morphology, with the exception of Diabrotica speciosa. The diploid chromosome number, the morphology of chromosomes, the type of sex determination, the pattern of constitutive heterochromatin distribution and the chromosomes bearing the nucleolus organizer regions (NORs) were studied in specimens from 3 different Brazilian populations of D. speciosa. The analysis of mitotic cells revealed 2n=21 in the males and 2n=22 in the females. All the chromosomes of the complement were metacentric and the type of sex determination was XO/XX. Additionally, mitotic metaphases of 1 female from the Ponta Grossa population showed the occurrence of heteromorphic homologous chromosomes in pair 9. The male meiocytes showed 10 bivalents and a univalent X chromosomes. One or 2 chiasmata were found per bivalent in diplotene. The constitutive heterochromatin was found in the centromeric region of all the autosomes and in both arms of the X chromosome. Besides, some autosomes of 1 specimen from the Ponta Grossa population were heteromorphic for C bands. NORs were found the telomeric region of pair 9 in all the individuals of the populations.