FIGURE 1.

Long periods of light and/or temperature synchronize locomotor activity in the linden bug, Pyrrhocoris apterus. Adult males raised under long photoperiod D6:L18 at 25°C were entrained for 5 days either by long photoperiods (A,B), long thermoperiods (C), or combination of both light and temperature (D) and released to constant dark at either 25°C (A) or 18°C (B–D). Double-plotted actograms represent the average activity of all males rhythmic under DD conditions [see panel (F) for the rhythmicity]. Detailed activity profile is plotted from all males for day 5–7 [right panels in (A–D)]. The actual temperature recorded during the experiment is shown in red (right y-axis). The rhythmicity under constant conditions was determined from 10 days and is presented as the free-running period of each individual male (dots) and mean ± SEM shown in magenta (E), there is no difference in the free-running period between groups (p > 0.05, Kruskal–Wallis). The same small letters above categories indicate no statistical difference. The percent of arrhythmic, weakly rhythmic and strongly rhythmic males is shown in panel (F).