Abstract
The testes obtained from diapausing rice stem borer larvae were cultivated in the medium CSM-2F, lacking any insect blood, in order to investigate the morphological changes of male germ cells in vitro, and it was ascertained that spermatogenesis was occasionally induced in the testes considerably a long time after the onset of cultivation. Further study was carried out to make sure the effect of a moulting hormone, ecdysterone, on the testes in vitro. From the results showing a remakably rapid development of both testes and spermatocysts of the diapausing larvae, it was concluded that ecdysterone acted to promote spermatogenesis of the rice stem borer larvae.
