Abstract

PIP: The egg production and laying rhythms in the fruit fly were examined in constant darkness, a photoperiod of LD 12:12 and after switching from photoperiodic conditions to darkness. The flys were adult F1 heterozygotes (Brazzaville x Libreville); they were examined at 9, 14, and 19 hours and classified according to the terminology of King. In alternating light and dark there was a rhythm in egg production, with decreasing numbers of immature and increasing numbers of mature eggs during the photoperiod. Flies reared in total darkness kept their egg production rhythm for at least 5 days, but lost their rhythm of oviposition which ordinarily took place at the beginning of darkness. Removal of an egg-laying substrate also resulted in egg retention. Therefore, vitellogenesis has an endogenous circadian rhythm, while oviposition is dependent on light conditions.