Karyotype, sex chromatin and sex chromosome differentiation in the carob moth, Ectomyelois ceratoniae (Lepidoptera: Pyralidae)

This paper reports results of the first cytogenetic investigation carried out in the carob moth, Ectomyelois ceratoniae Zeller, the serious polyphagous, pest of both stored products and field crops in the Mediterranean basin and Near East regions. Preparations of mitotically dividing spermatogonia and oogonia revealed that the carob moth karyotype consists of 2n = 62 chromosomes. As typical for Lepidoptera, the chromosomes were of a holokinetic type, only slightly differed in their sizes, and displayed no morphological structures including primary constrictions (the centromeres) that could enable us their identification. Metaphase I spermatocytes showed 31 bivalents. Accordingly, 31 chromosome elements were observed in metaphase II spermatocytes. Hence the haploid chromosome number is n = 31. In pachytene complements, two NOR bivalents were observed. In highly polyploid nuclei of the Malpighian tubule cells and silk glands, females showed a heterochromatin body, the so-called sex chromatin or W chromatin, that was absent in male nuclei. This indicated that the carob moth possesses a WZ/ZZ sex chromosome system. However, we failed to identify the sex chromosome bivalent WZ in pachytene oocytes. In order to differentiate the sex chromosomes, we employed genomic in situ hybridization (GISH) and comparative genomic hybridization (CGH). GISH detected the W chromosome by strong binding of the Cy3-labelled, female-derived DNA probe. With CGH, both the Cy3-labelled female-derived probe and Fluor-X labelled male-derived probe evenly bound to the W. This suggested that the W is composed predominantly of repetitive DNA sequences occurring scattered in other chromosomes but accumulated in the W chromosome.