A CHROMOSOME STUDY OF 7 SPECIES OF INDIAN COLEOPTERA (MELOIDAE, TENEBRIONIDAE AND COCCINELLIDAE)

Chromosome formulae, behaviour of meiotic chromosomes and interspecific chromosomal homology in seven coleopteran species belonging to families, Meloidae, Tenebrionidae and Coccinellidae have been reported. Out of them, five species (Mylabris thunbergi of Meloidae, Pachycera? coromandelensis and Alphitobius laevigatus of Tenebrionidae and Epilachna sp. and Micraspis inops of Coccinellidae) have 20 chromosomes in the respective diploid complements and two species, i.e. 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. Evolution of karyotype through loss of y, loss/addition of chromatin, gene level changes and heterochromatinisation has been suggested for these celeopteran families.