Time measurement in the photoperiodic induction of sexual rest in the terrestrial Isopod Armadillidium vulgare (Latreille)

The photoperiodic control of sexual rest in Armadillidium vulgare was inves tigated using various experimental protocols. When reared in conditions of a Nanda-Hamner (i.e. resonance) protocol from their first parturial moult t o their post experimental moult females showed a weak resonance effect in s exual rest incidence. The transfer from a long day cycle to a symmetrical s keleton photoperiod-consisting of two equal light pulses per 24 h of contin uous darkness-revealed the involvement of a circadian oscillatory system in the photoperiodic clock of this species. The data, obtained in the whole e xperiments, suggested that both oscillator and hourglass features are invol ved in the photoperiodic response controlling the sexual rest in Armadillid ium vulgare. Moreover, when non-24-h light-dark cycles (with a long photoph ase) were applied, a mechanism responsible of arrest of reproduction also i mplied a photoperiodic counter which accumulated and added up the photoperi odic information within a sensitive period during post parturial intermoult . (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevi er SAS.