Chromosomal characterization of a tropical midge
B. B. Nath* and N. N. Godbole
Department of Zoology, University of Pune, Pune 411 007, India (*Reprint address)
Key words: karyology, Chironomus ramosus, polytene chromosome, tropical midge
Cytogenetic studies were carried out with Chironomus ramosus, which is a
widespread species among the tropical midges (Diptera: Chironomidae). This
work is a first attempt to examine the salivary gland polytene chromosomes as
well as the ganglionic mitotic chromosomes of this species. A detailed cyto-
photomap for each chromosome (n =4) was prepared. Distinctive features of all
the chromosomesare described. The results have been compared with other .
known species of tropical.chironomids.
Chironomid midges are. dipteran insects. They abound in most
freshwater environments and seem to have a remarkably wide range
of tolerance for different ecosystems (Oliver, 19:z.1;Pinder, 1986). The
ease with which cytogenetic work can be carried out with these insects
is largely due to the high degree of polyteny in larval tissues
Polytene chromosomes provide a very important tool in evolu-
tionary cytogenetics, and Chironomus ramosus is a useful model
(Martin, 1979). The Chironomus genus belongs to an ancient group
of dipteran insects (Suborder Nematocera), and it is separated
from Drosophila melanogasterby approximately 200 million years of
evolution (Curtis et al., 1995).
Several papers on karyotypic evolution in the genus Chironomus
have been published, mainly on temperate species (Keyl, 1962;
Martin et ai., 1974; Martin, 1979; Wulker, 1980). Unfortunately,
tropical species of Chironomus have not attracted much attention.
However, in recent years, chromosomes of several species of tropical
midges have been described from the Indian subcontinent (Saxena
et al., 1985; Nath and Lakhotia, 1989; Kumar and Gupta, 1990;
Gupta and Kumar, 1991; De and Gupta, 1994).
Chironomus ramosus is a new species described by Chaudhuri et al.
(1992). The current study is an attempt to characterize the chromo-
somes of C. ramosus and prepare a reference cytophotomap of salivary
gland polytene chromosomes for future cytogenetic studies.
25 Cytobios 91 25-31 1997 Published and @ 1997 by The Faculty Press
88 Regent Street, Cambridge, Great Britain