CIRCADIAN RHYTHMICITY IS INVOLVED IN PHOTOPERIODIC TIME MEASUREMENT IN THE APHID MEGOURA-VICIAE

The photoperiodic clock in the vetch aphid Megoura viciae is generally accepted to be based on a non-circadian mechanism or ''hourglass'', a s no evidence has been found for the involvement of the circadian syst em in the photoperiodic response. By using a recently-devised protocol which discriminates between single and repeated night length measurem ent, we demonstrate here that long-night measurement in Megoura is exe cuted in a repetitive way, and thus that its photoperiodic clock is ba sed on a circadian oscillator after all. However, it is also apparent that the determination of short nights is not repetitive.