Effects of constant light on the rhythm of adult locomotor activity in the blowfly, Calliphora vicina

Abstract. Females of the blowfly, Calliphora vicina , showed an increase in the free-running period (γ) of their locomotor activity rhythm when transferred from continuous darkness (DD) to continuous 'dim' light (LL) at an irradiance below about 0.03 Wm^-2. Transfer to LL of this intensity also caused a reduction in the duration of the active phase (α) of the cycle. Transfer to 'bright' light (>0.03 Wm²), however, lead to arrhythmicity. Data suggest that constant light of this intensity does not 'stop' the circadian pacemaker but imposes behavioural arrhythmicity at a more superficial level.