Geographic variation in the circadian system controlling photoperiodism inOstrinia nubilalis

Abstract

1. The critical daylength for diapause induction is temperature dependent in three geographic strains ofOstrinia nubilalis. Critical daylength increases as the temperature is lowered, as does the general level of diapause. 2. The critical daylength and general level of diapause are also strain dependent at two constant temperatures (20 °C and 30 °C). The northern strain shows a longer critical daylength than the southern strains. The northern strain also shows a greater tendency to diapause at both temperatures. 3. Whether or not Nanda-Hamner experiments yield positive (induction of diapause rising and falling approximately every 24 h) or negative (nonrhythmic) results is a function of the strain being examined and the temperature of the experiment. The northern strain shows a nonrhythmic hourglass response at 20 °C but circadian periodicity at 30 °C. Conversely, southern strains show a nonperiodic pattern at 30 °C but circadian periodicity at 20 °C. 4. The results from Nanda-Hamner experiments are compatible with the pacemaker-slave model for circadian rhythmicity and photoperiodism recently proposed by Pittendrigh (1981).