Responsiveness to light of the circadian clock controlling eclosion in the blowfly, Lucilia cuprina

ABSTRACT. Eclosion in Lucilia cuprina (Wiedemann) occurs near dawn. The rhythm of eclosion persists in both darkness and constant light of high intensity (490μW cm^-2) with a period close to 24h. The sensitivity to light of the circadian clock controlling eclosion varies greatly according to the stage of the life cycle. During larval life the free running rhythm in darkness can be phase shifted by light pulses of 100μW cm^-2 intensity, with the transition from a Type 1 phase response curve to a Type 0, occurring with pulses of between 1 and 8h. Extending the last light period of LD to 24 h followed by constant darkness resets the phase of the rhythm by 12h, a transition from constant light to constant darkness initiates rhythmicity in flies made arrhythmic by being reared from eggs collected from adults maintained in constant light. After pupariation, the rhythm is relatively insensitive to light. Rhythmicity is sometimes induced by a transition from constant light to constant darkness, but the phase of the rhythm is not shifted by extending the last light period of LD before entering constant darkness. Repeated LD cycles applied after pupariation initiate and entrain the rhythm.