Karyotype and meiotic behaviour of the holokinetic chromosomes of six Argentine species of Pentatomidae (Heteroptera)

The Pentatomidae are one of the largest families of Heteroptera with approximately 250 species cytogenetically analyzed. They possess holokinetic chromosomes, a modal diploid number of 14 (range 6-27) and a sex chromosome determining system XY/XX. Male karyotype and meiosis of Proxys albopunctulatus, Dichelops furcatus, Piezodorus guildinii; Loxa deducta (Pentatominae); Dinocoris prolineatus and Macropygium reticulare (Discocephalinae) from Argentina are analyzed. All these species are 2n= 14 (12 + XY), except D. furcatus with 2n= 12 (10 + XY) as consequence of an autosomal fusion. Meiosis follows the typical pattern of the order Heteroptera (pre-reduction of autosomes, post-reduccion of sex chromosomes, and ring arrangement of autosomes at both metaphase plates with sex chromosomes inside it). These species show a great constancy in the diploid number, but some differences in the karyotype and meiotic behaviour are encountered (relative size of sex chromosomes, characteristics of the diffuse stage). In all the species except in M. reticulare, bivalents with two chiasmata are observed. We suggest that ring bivalents are not so uncommon as it has been previously supported.