Reproductive physiology of male moths is regulated by a peripheral circadian system, which controls the timing of sperm release from the testis into the upper vas deferens (UVD) and timing of sperm transfer from the UVD to the seminal vesicles. We investigated various effects of light and temperature on sperm release and transfer rhythms in the moth Spodoptera littoralis. We report that both rhythms persist for up to 1 week in constant darkness without significant dampening and are also temperature compensated in the range from 20 degrees C to 30 degrees C. However, the duration of sperm retention in the UVD is temperature-dependent; consequently, temperature exerts a masking effect on the rhythm of sperm transfer. Experimental manipulations of light and temperature regime demonstrated that light dominates over temperature in entraining the timing of sperm release and transfer. Nevertheless, temperature plays a critical role in the absence of light Zeitgeber. Sperm release and transfer are arrhythmic in constant light (LL); however, both rhythms are restored by temperature cycles.