Effect of photoperiod on the duration of summer and winter diapause in the cabbage butterfly, Pieris melete (Lepidoptera: Pieridae)

Effect of photoperiod on the duration of summer and winter diapause was investigated in the cabbage butterfly, Pieris melete. By keeping naturally induced aestivating and hibernating pupae under various photoperiods, it was shown that diapause duration of aestivating pupae was significantly longer at long than at short daylengths, whereas diapause duration of hibernating pupae was significantly shorter at long than at short daylengths, suggesting both aestivating and hibernating pupae require opposite photoperiodic signals to promote diapause development. By transferring diapausing pupae, induced under various photoperiods, to 20°C with a naturally changing summer daylength, the diapause induced by short daylengths was easier to terminate than diapause induced by long daylengths. When naturally induced aestivating and hibernating pupae were kept under natural conditions, aesti- vating pupae had a long diapause (mean 155 days) and wide range of emergence (90 days), whereas hibernating pupae had a short diapause (mean 105 days) and a relatively synchronized emergence (lasted 30 days). Finally, the ecological significance of photope- riodic regulation of diapause duration is discussed.