Heterochromatin and rdna localization on the holocentric chromosomes of black bean aphid, aphis fabae scop. (hemiptera: Aphididae)

Heterochromation and rDNA localization in the holocentric chromosomes of the aphid Aphis fabae has been investigated at a cytological level after C-banding, Giemsa, DAPI, CMA3 and NOR staining. C-banding technique showed that heterochromatic areas result mainly clustered on the X chromosomes but, contrary to what observed in other aphid species, in A. fabae C-positive bands are clearly distinguishable also on each autosomal chromosome pair, thus allowing the identification of homologues and a reliable reconstruction of the karyotype. Moreover, silver staining localized rDNA genes on one telomere of each X chromosome; these are the only brightly fluorescent C-positive regions revealed after CMA3 staining, whereas all other heterochromatic bands are DAPI positive. Both CMA3 and silver staining evidenced a noticeable amount of rDNA heteromorphism.