Giemsa banding of metaphase chromosomes in triatomine bugs

Abstract

CONSIDERABLE progress has been made in developing the formal genetics and cytogenetics of several insect vectors of disease^1,2, notably with mosquitoes, houseflies and tsetse flies in which the polytene chromosomes provide suitable material for detailed analysis of chromosome morphology. The triatomine bugs (Hemiptera, Reduviidae) are medically important as vectors of Chagas' disease in the Americas, yet cytogenetic information on these insects is meagre^3–8. These bugs present the same problems which, until recently, limited developments in mammalian cytology in that they possess a large number (typically 2n = 22) of small, almost indistinguishable chromosomes⁷. Further, since their chromosomes are also holokinetic⁹ (that is with non-localised centromeres) they do not show any primary constrictions and it is correspondingly difficult to recognise arms of a chromosome which are readily seen in chromosomes of organisms possessing discrete centromeres. This difficulty with triatomine material has now been overcome by applying the Giemsa staining methods, which have been effectively developed by mammalian cytologists^10–13, to embryonic cells of bugs with metaphase configurations. The technique I describe here makes possible the identification of individual chromosomes within the complements of different species of triatomine bug.