Karyotype, heterochromatin distribution and meiosis of Zabrotes subfasciatus (Bohemann) (Coleoptera: Chrysomelidae, Bruchinae)

Zabrotes subfasciatus (Boh.) has been extensively studied in its agronomic and biochemical aspects due to its importance as a damaging insect to leguminous grains during storage. The few cytogenetic studies published on this species yielded conflicting results. In this study, the karyotype was analyzed in order to accurately describe the chromosome C-banding patterns and meiosis. The brain ganglion at the prepupa and the adult and pupal testes were analyzed. All individuals had 26 chromosomes in both brain ganglion and spermatogonic mitotic metaphases. These chromosomes were classified as follows: the 12th pair and the Y chromosome were telocentric; the X chromosome was acrocentric; the 4th and 5th pairs were submetacentric; and the remaining pairs were all metacentric. One of the members of the 5th pair presented a secondary constriction. All chromosomes presented pericentromeric heterochromatin. The large arms of the pairs 5, 9 and X presented heterochromatin. The X chromosome showed to be heteropyknotic throughout the prophase of the first meiotic division. The subphases of prophase I were atypical and meiosis II was rarely identified. Testes of all males showed a few cells; the bivalents were rod-like shaped in metaphase I. Karyological formulae were 2n = 24 + XX in females and 2n = 24 + XYp and either n = 12 + X or n = 12 + Y in males. Zabrotes subfasciatus (Boh.) é estudada intensivamente em termos agronômicos e bioquímicos por causar danos aos grãos de leguminosas armazenados. No entanto, os dados publicados sobre o seu cariótipo são escassos e conflitantes. Assim, o objetivo deste estudo foi descrever o cariótipo e a meiose desse inseto e analisar o padrão de bandas-C de seus cromossomos. Foram analisados os gânglios cerebrais de pré-pupas e os testículos de adultos e pupas com adaptação de uma técnica que permitiu boa qualidade de preparo dos cromossomos dessa espécie. Todos os indivíduos apresentaram 26 cromossomos nas metáfases mitóticas. Esses cromossomos foram classificados em: acrocêntricos (cromossomo X); submetacêntricos (pares 4 e 5); subtelocêntricos (par 12 e cromossomo y); metacêntricos (demais pares). O cromossomo 5 apresentou uma constrição secundária. Todos os cromossomos apresentaram heterocromatina próximo ao centrômero e os cromossomos 5, 9 e X, nos braços longos. O cromossomo X mostrou-se heteropicnótico durante toda a prófase da primeira divisão meiótica. As subfases da prófase I foram pouco distintas e a meiose II de difícil id