Abstract: The authors conducted qualitative and quantitive studies on spermatogenesis and spermiogenesis in Agrotis ypsilon and Mythimna separata with use of light and electron microscopes. At the same time, the effects of risen temperature were also studied. The results are briefly summarized as follows: There were eupyrene and apyrene sperms in A. ypsilon and M. separata after spermatogenesis. When the rearing temperature rose above 32℃, a lot of abnormal spermatid cysts appeared and spermiogenesis was arrested. In addition, the nucleus and flagellum of eupyrene spermusually shortened and a large amount of flagellum microtubles could not be produced under this temperature. But the risen temperature (<32℃ ) had no effects on dichotomous spermatogenesis and the shift of spermatogenesis from eupyrene sperms to apyrene. This phenomenon implies that the migratory flight of A. ypsilon and M.Separata in summer season from south toward north is an adaptive behavior.

Key words: Agrotis ypsilon, Mythimna separata, spermatogenesis, spermiogenesis