SUMMER AND WINTER DIAPAUSE IN PUPAE OF THE CABBAGE BUTTERFLY, PIERIS MELETE MENETRIES

The cabbage butterfly, Pieris melete is multivoltine with a pupal summ er and winter diapause, Summer and winter diapause are induced princip ally by relatively long and short daylengths, respectively, The interm ediate to relatively short daylengths of autumn permitted some pupae t o develop without diapause in the field, A short daylength had a stron ger diapause inducing effect than a relatively long one under higher t emperatures, The principal sensitive phase for photoperiodic response occurred before the late 3rd Larval instar, The critical daylength for wild autumnal populations was between 12 h 30 min and 12 h 40 min at an average temperature of 20.5 degrees C. A night interruption by 2 h of light averted diapause most effectively when it was placed 10 to 12 h after lights-off, High temperatures and long days during summer inh ibited the incidence of diapause, suggesting that the occurrence of su mmer diapause is due to the specific climatic conditions occurring in April and early May, rather than to the high temperatures in summer, T his indicates that the butterfly has a cryptic ability to reproduce in summer, High temperatures delayed diapause development, whereas low t emperatures enhanced it, indicating that the optimum temperature of di apause development is lower, The diapause regulating mechanisms thus e nsure that the species synchronises its development and reproduction w ith the growth seasons of the host plants and provide the species with a high degree of flexibility in its life cycle. (C) 1997 Elsevier Sci ence Ltd.