A CHROMOSOMAL INVESTIGATION OF 2 CLOSELY-RELATED SPECIES OF SPODOPTERA

This paper reports the first cytogenetic study of the two closely rela ted species of noctuid moths, Spodoptera latitascia 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 metaphas es, which allowed chromosomes to be counted. For both species and F1 h ybrids, the diploid chromosome number was 2n = 62. The chromosomes of the two species appeared dot-shaped, more rarely rod-shaped, showing l ittle variation in size or morphology. The preparations from larval br ains also suggested the existence of two levels of ploidy (haploidy an d diploidy) in some nuclei. This result will need further investigatio n. For the first time in the Lepidoptera, in situ hybridization with D rosophila rDNA as a probe was carried out on S. latifascia and S. desc oinsi. It revealed the presence of nucleolar organizing regions locate d at the dietal part of one chromosome pair. Though no sophisticated c haracterization of S. latifascia and S. descoinsi was possible, it see med that there was no major chromosomal difference. No karyotypic elem ent could be identified as being involved in reproductive isolation be tween the two species. ((C) Academie des sciences/Elsevier, Paris.)