paramjeet kaur

Three species of genus Onthophagus viz. O. catta Fabr., O. falsus Gill, O. bonasus Fabr. displayed a male meio-formula 9AA + Xy with 2n = 20 chromosomes. The fourth species Sisyphus neglectus Gory presented meio-formula of 7AA + Xyp with 2n = 16 chromosomes. O. falsus and Sisyphus neglectus are new additions to the cytological data of beetles.

The aim of present study was to describe the karyotype of species belonging to the genus Onthophagus and to compile the conventional cytogenetic data available in the literature for this group. Chromosomal investigations on three Onthophagus spp. viz. O. fasciatus (Boucomont, 1914), O. unifasciatus (Schaller, 1783) and O. bifasiatus (Fabricius, 1781) were analysed using conventional staining and C-banding. All the three species possessed 20 chromosomes and a modal polyphagan karyotype with Xyp as the male sex chromosome mechanism. Most of the autosomal chromosomes were metacentric or submetacentric, while X and y showed acrocentric nature. Modal chromosome number of these species showed the conservative nature of the karyotype. C-bands were located predominantly at peri-centric position. Along with this chiasma frequency, terminalisation coefficient and sperm number count were also calculated which again showed a close relationship among these species.

The chromosomes obtained from meloid beetle Mylabris pustulata Thumb. of subfamily Meloinae was studied using standard staining and C-banding. The cytological information of beetles is useful in many ways. Theoretically, it is important to understand the mechanism governing the transmission of genetic information, hence speciation and for classification on taxonomic levels. It is also useful in the field of applied economic entomology for the improvement of species. The karyotype of Mylabris pustulata, is comprised of 22 chromosomes with meioformula, 10AA+Xyp. The analysis of constitutive heterochromatin (CH) revealed small blocks located in the terminal regions of dumbbell shaped bivalents in metaphase I. The increased in chromosome number from 20 (Modal number) to 22 and with conserved sex chromosome mechanism in Mylabris pustulata as compared to other species of this family is suggestive of the Robertsonian fission of autosomes having played some role in the evolution of karyotype in this family.

The chromosomal analysis of beetle Hoplopoderus gemmeatus Thunberg. of subfamily Attelabidae and tribe Hoplop Soderini was done using standard staining, C-banding and AgNO3 banding. Tribe Hoplopoderini was first time mapped cytogenetically. The cytological information of these beetles is useful in many ways. Theoretically, it is important to understand the mechanism governing the transmission of genetic information, hence speciation and for classification on taxonomic levels. It is also useful in the field of applied economic entomology for the improvement of species. The karyotype of Hoplopoderus gemmeatus, is comprised of 30 chromosomes with meioformula, 14AA+Xyp. The analysis of constitutive heterochromatin (CH) revealed small blocks located in the centromeric regions of chromosomes, whereas silver staining revealed the silver dark spots corresponding to the nucleolar organizing region. The increased in chromosome number from 20 (Modal number) to 30 and with conserved sex chromosome mechanism in Hoplopoderus gemmeatus as compared to other species of this family is suggestive of the Robertsonian fission of autosomes having played some role in the evolution of karyotype in this family.

The family Scarabaeidae comprises 25, 000 described species and is known cytologically by 404 species of 123 genera and 18 subfamilies. The present investigations recorded an account of 33 species representing 6 subfamilies, of which 17 species are new additions to this family. Scarabaeidae is conservative family in having the chromosome number 2n=20, sex determining mechanism "Xyp" and metacentric chromosomes. Most of the cytogenetically known species have a chromosome number varying from 2n=8 in Eurysternus caribaeus to 2n= 36 in Gymnopleurus miliaris race-II (present study). The most prevalent sex determining mechanism is Xyp. The most common karyotype possessed by 175 species belonging to 18 subfamilies is 9AA+Xyp male, the most prevalent condition in Coleoptera as a whole. As many as 302 species showed a haploid number of 10. So, this can be very well designated as the "modal number" for Scarabaeidae.

Karyological investigations on two Gymnopleurus spp.; Gymnopleurus miliaris (F.) and Gymnopleurus parvus (MacL.) are under taken in the present study. Meioformula of G. miliaris (17AA+Xyp) and G. parvus (8AA+Xyp) are presented. None of these beetles exhibited a modal polyphagan karyotype. However, Xyp was found to be the male sex chromosome mechanism. Most chromosomes are acro and subtelocentric. Change in the number and size of chromosomes in the karyotypes is suggestive of the Robertsonian fusion having played some role in the evolution of karyotype in this genus. The evolutionary trends in Gymnopleurus have been discussed.