Circadian rhythm of sperm release in males of the cotton leafworm, Spodoptera littoralis: in vivo and in vitro studies

We have investigated patterns of sperm release from the testes of the cotton leafworm, Spodoptera littoralis, a moth which produces an unusually high number of sperm bundles. In a daily cycle of 16 h of light followed by 8 h of darkness, penetration of sperm bundles through the epithelial barrier separating testicular follicles from the vasa deferentia was initiated approximately 5 h before lights-off and completed 10 h later. A clear rhythm of sperm penetration persisted in moths that were kept for three days in constant darkness, indicating a circadian nature. The release of anucleated sperm was followed, a few hours later, by the release of regular, nucleated sperm in both environments. To determine the factors controlling the timing of sperm release, we cultured testis–vas deferens complexes of S. littoralis in vitro and demonstrated that relatively large numbers of bundles were rhythmically released for at least two days in light–dark cycles and in constant darkness. These data suggest that the sperm release rhythm is controlled by an intrinsic circadian mechanism located in the reproductive system. The rhythmic release of sperm was lost and significantly reduced by constant light, both in vivo and in vitro. The results obtained in this study are compared with previous reports and it is concluded that the release of sperm in a rhythmic fashion may be a conserved feature in moth reproduction.