A chromosomal investigation of two closely related species of Spodoptera

Abstract

This paper reports the first cytogenetic study of the two closely related species of noctuid moths, Spodoptera latifascia and S. descoinsi. Chromosomes were prepared using a spreading technique on warm slides. Both gonads and larval brains, which are innovating in the Lepidoptera, were used. Out of 100 specimens observed, 35 showed mitotic metaphases, which allowed chromosomes to be counted. For both species and F1 hybrids, the diploid chromosome number was 2 n = 62. The chromosomes of the two species appeared dot-shaped, more rarely rod-shaped, showing little variation in size or morphology. The preparations from larval brains also suggested the existence of two levels of ploidy (haploidy and diploidy) in some nuclei. This result will need further investigation. For the first time in the Lepidoptera, in situ hybridization with Drosophila rDNA as a probe was carried out on S. latifascia and S. descoinsi. It revealed the presence of nucleolar organizing regions located at the distal part of one chromosome pair. Though no sophisticated characterization of S. latifascia and S. descoinsi was possible, it seemed that there was no major chromosomal difference. No karyotypic element could be identified as being involved in reproductive isolation between the two species.