Abstract
The effects of temperature and photoperiod on adult diapause in Chrysolina aurichalcea were investigated by rearing at various temperatures and photoperiods for Matsumoto and Yakushima populations. That all adults entered diapause under all experimental conditions, suggested that the diapause was obligatory for these populations. The diapause termination revealed a short-day response. The speed of termination increased with the decrease of photoperiod below the critical photoperiod. The critical photoperiods of diapause termination in Matsumoto population were 14 h at 15°C and 12 h at 25°C, and that in Yakushima population, 12.75 h at 15°C. The critical photoperiod was estimated to decrease about 1 h with the increase of 5°C of rearing temperature and about 8 min with the increase of 1°N latitude of native habitat. The response controlled the initiation of oviposition in autumn. The diapause was considered as functioning not only to survive at low mortality in the severe summer season but also to control the oviposition period so as to maximize the number of egg survivors when the sprout emergence of the host plant, Artemisia princeps occurs in early spring. The difference of their oviposition strategy between Matsumoto (cold winter : host plant leaves not available in winter) and Yakushima (warm winter : available in winter) were discussed in reference to the difference of the host plant phenology.
