IMPROVED RESOLUTION OF THE MEIOTIC CHROMOSOMES IN BOTH SEXES OFEUXOASPECIES AND THEIR HYBRIDS (LEPIDOPTERA: NOCTUIDAE)

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Abstract
An air drying and Giemsa staining technique produces consistently good quality cytological preparations when applied to different species of Euxoa (Lepidoptera: Noctuidae) and, in particular, it allows an improved resolution of the meiotic chromosomes in both sexes. All species so far investigated have a basic haploid chromosome complement of n(♀) = 31(XX); n(♂) = (XY). A single chiasma per individual bivalent is clearly visible in the male sex. Some chiasmata are formed in interstitial positions, but, by metaphase I, they have all undergone complete terminalization while the bivalents orient axially on the first division spindle. Direct evidence for lack of chiasma formation in the 31 hormorphic bivalents in the female sex is reported for the first time for species of Noctuidae. Evidence in favor of an XY system in the female sex is discussed. Preliminary studies of the meiotic divisions in hybrid material reveal the presence of cryptic structural differences between certain taxa, and will help to elucidate taxonomic problems within this complex genus.