Abstract. The Lygaeidae (Heteroptera) are a large and diverse family in which the male diploid chromosomal complement ranges from 10 to 30. Diploid numbers of 14 and 16 are taken as two modal numbers of the family. The Rhyparochrominae, one of the largest subfamilies of the Lygaeidae, are known to be heterogeneous both cytologically and morphologically. Available data on the tribe Rhyparochromini reveal that all species are characterized by the presence of a pair of microchromosomes (m-chromosomes) and have an XY/XX (♂/♀) sex chromosome determining system. Dieuches coloratus (Distant, 1909) and D. insignis (Distant, 1918) belonging to Rhyparochromini, have 2n=14=10A+2m+XY and 2n=12=8A+2m+XY respectively. Both the species are similar in having one pair of distinctly large autosomes in their chromosome complements. The metaphase plate arrangement of autosomes, sex chromosomes and m-chromosomes in D. coloratus is similar to the common condition observed in the tribe Rhyparochromini. In D. insignis, however, the arrangement is different. Here, metaphase I is usual in showing peripheral position of autosomes and central position of sex chromosomes and m-chromosomes. At metaphase II, however, autosomes, sex chromosomes and m-chromosomes are peripherally placed, an arrangement, which is not reported earlier in the tribe Rhyparochromini.

Although the karyotypes of twelve species of Dieuches Dohrn, 1860 belonging to Rhyparochrominae have been described so far, there is no information about heterochromatin and its characterization in terms of base composition for any of the species. In the present paper, C‐banding and fluorescent banding have been applied for the first time to three species of Dieuches: D. uniguttatus, D. insignis (2n = 12 = 8A + 2m + XY) and D. coloratus (2n = 14 = 10A + 2m + XY). Dieuches uniguttatus and D. insignis show distinct terminal C‐bands along with a few interstitial bands in all the autosomal bivalents, whereas in D. coloratus, one autosomal pair is almost completely heterochromatic, three show C‐positive bands while one is totally euchromatic. The sex chromosomes too show heterogeneity in distribution of C‐heterochromatin among three Dieuches species. Characterization of heterochromatin in D. uniguttatus and D. insignis using DAPI/CMA3 staining reveals that in D. uniguttatus, C‐ heterochromatin blocks of all the autosomal bivalents, which are predominantly A–T rich, whereas in D. insignis, these are rich both in A–T and G–C. In D. uniguttatus, sex chromosomes X and Y have localized G–C rich regions whereas in D. insignis, these are scattered in X and absent in Y. As variations in the heterochromatin represent the main source of karyological differentiation among and within species, it seems that there occurred extensive redistribution of heterochromatin within the complement as the three species evolved. There is need for cytological details of more species to understand evolutionary aspects in the genus Dieuches.

Summary Eurydema pulchrum Westw. and Bagrada cruciferarum Kirkadly (Pentatomidae) show 2nϭ14ϭ12AϩXY. Autosomes show gradation in size, X is of medium size while Y is the smallest element. Both X and Y are positively heteropycnotic in diffused stage but become isopycnotic in diplotene stage and divide equationally during meiosis-I. At metaphase-II, X and Y get associated, the association being strong forming a pseudobivalent XY in Eurydema pulchrum while weak in Bagrada cruciferarum. A definite pattern of arrangement of the chromosomes is seen at metaphase-II.Cletus bipunctatus Westw. and Serinetha augur Fabr. (Coreidae) show 2nϭ17ϭ14Aϩ2mϩXO and 2nϭ13ϭ10Aϩ2mϩXO respectively. The complement in both the species is conspicuous by the presence of 2 microchromosomes and absence of Y element in males. Microchromosomes form achiasmatic bivalent at meiosis-I. X undergoes equational division at metaphase-I while at metaphase-II it remains outside the metaphase plate and is added to one of the pole as a precocious element in Cletus bipunctatus and as a laggard in Serinetha augur.Key words Chromosomes, Meiosis, Pentatomidae, Coreidae.The family Pentatomidae, one of the major families of Heteroptera, includes shield-shaped bugs which are commonly called stink-bugs due to the presence of stink glands. Members of the family Coreidae are called squash bugs or leaf-footed bugs and are characterized by the presence of scent glands on the thorax. Family Pentatomidae is noted for its extreme karyotypic conservation. Earlier knowledge about the cytology of this family is largely due to the contribution made by Gupta (1950), Manna (1951, Rao (1954), Dutt (1955, Hughes-Schrader and Schrader (1957), Parshad (1957b) and Schrader and Hughes-Schrader (1958). The family Coreidae is characterized by the presence of a pair of very small chromosomes which behave differently from both autosomes and sex-chromosomes during meiosis (Wilson 1905). The present paper includes the study of diploid complement and behavior of autosomes and sex chromosomes during meiotic cycle in four North Indian heteropteran species belonging to Pentatomidae and Coreidae. Materials and methodsSpecimens of Eurydema pulchrum Westw., Bagrada cruciferarum Kirkadly. (Pentatomidae) and Serinetha augur Fabr. (Coreidae) were collected from Patiala (Punjab) while those of Cletus bipunctatus Westw. (Coreidae) were collected from Palampur (Himachal Pradesh). Male bugs of each species were dissected to take out the testes which were fixed in ethanol : glacial acetic acid (3 : 1) and air dried chromosomal preparations were stained in carbolfuchsin stain.

Summary Reduviids comprise the largest family of predaceous land Heteropterans and are characterized by a modal autosomal diploid number of 20 with both simple and multiple sex chromosome systems. Multiple systems are more frequent in Harpactorinae and Stenopodainae. Microchromosomes are invariably absent in this family. Stenopodainae have a diploid autosomal number of 20/22 (nϭ10A/11A) plus different multiple sex chromosome systems (XnY/XnXn). In the present work the chromosome complement and course of meiosis of two species viz. Oncocephalus notatus (2nϭ23ϭ20AϩX 1 X 2 Y) and Sastrapada baerensprungi (2nϭ23ϭ20AϩX 1 X 2 Y) (Stenopodainae) collected from the Punjab region of India and new to the cytogenetic world, are described.

SummaryIn the present study, 5 species of Lygaeidae and 1 each of Berytidae and Malcidae have been cytologically investigated for the first time; the diploid numbers in them vary from 12 to 20. Out of the 5 lygaeids, male diploid number is 12=8A+2m+XY in Dieuches leucoceras and Polycrates nexus while being 14=10A+2m+XY in Aphanus orientalis, Lanchnophorus sp. and Mizaldus sp. A pair of extremely large autosomes is found in both the species with 2n=12 while it may or may not present in species with 2n=14. One species each of Berytidae (Metacanthus pulchellus) and Malcidae (Malcus flavidipes) show 2n=20=18A+XY and 2n=16=12A+2m+XY respectively, and both lack an extremely large pair of autosomes. Microchromosomes are present in Lygaeidae (Rhyparochrominae) and Malcidae but absent in Berytidae. The sex determining mechanism in all the species of 3 families is XY/XX (♂/♀). Fragmentations seem to have played a pivotal role in the origin of new species irrespective of family.