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Male meiosis and karyotypes of 5 species of Indian Heteroptera (Megacopta cribraria of Plataspidae and Coridius ;anus, Andrallus spinidens, Nezara viridula and Gynenica affinis of Pentatomidae) are analysed. Diploid number of 2n = 12, XY inM. cribraria, 2n = 14, XY in C. ;anus, A. spinidens and N. viridula and 2n = 16, XY in G. affinis are recorded. During karyotypic evolution, mechanisms like minor interchromosomal changes in Plataspidae and fragmentation and interchromosomal changes in Pentatomidae are suggested to have operated.

Mylabris pustulata of Meloidae and Hoplobrachium dentipes of Tenebrionidae, have 2n = 22. The sex mechanism is found to be Xyr in three species (M. thunbergi, M. pustulata and H. dentipes) and is Xyp in the rest. Metacentry, heteropycnotic sex chromatin in the resting nucleus, terminal chiasma, monochiasmate bivalents, diffuse diplotene etc. are some of the common cytological features of all these species.

Intraspecific and intraindividual variation in chromosome number in aphids is not un common (Lauritzen 1982, Manna 1983, Pal and Khuda-Bukhsh 1985a, b, Kurl 1986 . Chromosomes of this group of insects are universally suggested to be holocentric and fragile. It has been experimentally proved that fragments of holocentric chromosomes are mitotically stable (Hughes-Schrader and Schrader 1961). Thus numerical variation of chromosomes within a species cannot be always dismissed as an occasional phenomenon which rather war rants analysis from cytoevolutionary context. The aims of the present investigation are to study the evolutionary significance of such differences among clones of 5 species of aphids collected from same or different host plants in relation to host plant preference. Table 1. Place of collection, name of host plant and chromosome number of different clones of aphid species of this study Material and methodsEarly embryos from apterous viviparous females of 5 species of aphids (Table 1) were dissected out in 0.4% KCl containing 0.05% colchicine and incubated in the same solution for at least 20min. The material was squashed after fixation in a drop of 50% acetic acid and the coverslip was removed in 1:3 acetomethanol. Staining was done in 3% Giemsa (pH=6.8). The slides were dried in the air and mounted in DPX. Chromosomes were meas ured from 10 selected metaphases in each case. ResultsThe mitotic process in all these 5 species of aphids is typical.

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