Effects of Ecdysterone and C18-Juvenile Hormone on Spermatogenesis in the Silkworm Larva, Bombyx mori L.

Abstract

In Bombyx mori spermatogenesis promotes with the formation of primary spermatocytes in the 4th instar, but spermiogenesis does not begin until about 24 hours after ecdysis to the 5th instar. C-juvenile hormone (JH) application (100 μg/larvae) delays the onset of spermiogenesis by 4 days. Conversely, allatectomy in the 3rd instar causes the onset of spermiogenesis 4 days later in preparation for precocious pupation.Spermiogenesis occurred normally in 4th-instar abdomens ligated 72 hours after ecdysis, but oinly partially in abdomens isolated before that time. Ten μg ecysterone enhanced the growth of these latter testss (by initiating meiosis), but did not increase the percentage undergoing spermiogenesis. JH prevented spermiogenesis in all cases.Testis from 24 to 48-hour-old 4th instar larvae showed spermiogenesis after in vitro culture in day 4 5th-instar hemolymph or in modified GRACE's medium. Ecdysterone was not required, but JH added to the in vitro medium inhibited spermiogenesis. Thus, ecdysterone is necessary to initiate meiosis in the spermatogonia resulting in the formation of primary spermatocytes. JH inhibits the further differentation of these primary spermatocytes until its level declines in the last larval instar in preparation for metamorphosis.