http://www.eje.cz response, occurs in advance of diapause, the most extreme example of which is when this sensitive stage occurs in one generation and diapause in the next (i.e. a maternal effect) (Mousseau & Dingle, 1991).The circadian clock that regulates the rhythm of locomotor activity comprises at least a dozen circadian clock genes, including period (per), timeless (tim), mammaliantype cryptochrome (cry-m or cry2), cycle (cyc), Clock (Clk), Par domain protein 1 (Pdp1), vrille and clockwork orange (Tomioka, 2014;Tomioka & Matsumoto, 2015; Patke et al., 2020). The principal mechanism associated with these genes is a transcription-translation feedback loop, which takes approximately 24 h to complete. Involvement of the circadian clock in photoperiodic time measurement was fi rst proposed by Erwin Bünning in the 1930s (Bünning, 1936), and subsequently, further models were proposed, initially a modifi ed version of Bünning's original model, referred to as the 'external coincidence model', and thereafter an alternative hypothesis, the 'internal coincidence