Optimal low temperature and chilling period for both summer and winter diapause development in Pieris melete: based on a similar mechanism

Abstract

The cabbage butterfly, Pieris melete hibernates and aestivates as a diapausing pupa. We present evidence that the optimum of low temperature and optimal chilling periods for both summer and winter diapause development are based on a similar mechanism. Summer or winter diapausing pupae were exposed to different low temperatures of 1, 5, 10 or 15°C for different chilling periods (ranging from 30 to 120 d) or chilling treatments started at different stages of diapause, and were then transferred to 20°C, LD12.5:11.5 to terminate diapause. Chilling temperature and duration had a significant effect on the development of aestivating and hibernating pupae. The durations of diapause for both aestivating and hibernating pupae were significantly shorter when they were exposed to low temperatures of 1, 5 or 10°C for 50 or 60 days, suggesting that the optimum chilling temperatures for diapause development were between 1 and 10°C and the required optimal chilling period was about 50-60 days. Eighty days of chilling was efficient for the completion of both summer and winter diapause. When chilling periods were ≥90 days, the durations of summer and winter diapause were significantly lengthened; however, the adult emergence was more synchronous. The adaptive significance of a similar mechanism on summer and winter diapause development is discussed.

Figure 1. Cumulative percentage of butterfly eclosion in summer diapausing pupae of P. melete.

The summer diapausing pupae were transferred to LD12.5∶11.5 at 20°C after exposure to 5°C and DD for different days. The hatched bar indicates the period of cold exposure under constant darkness. Data were shown as the median (minimum value–maximal value); values followed by different letters are significantly different by Bonferroni test (P<0.05).

Figure 2. Frequency distribution of adult eclosion in summer diapausing pupae of P. melete.

The summer diapausing pupae were transferred to LD12.5∶11.5 at 20°C after exposure to 5°C and DD for different days. The hatched bar indicates the period of cold exposure. Values followed by different letters are significantly different by Kruskal-Wallis test and Bonferroni multiple comparison (χ² = 224.312, d.f. = 3, P = 0.0001<0.01).

Figure 3. Frequency distribution of adult eclosion in winter diapausing pupae of P. melete.

The winter diapausing pupae were transferred to LD12.5∶11.5 at 20°C after exposure to 5°C and DD for different days. The hatched bar indicates the period of cold exposure. Values followed by different letters are significantly different by Kruskal-Wallis test and Bonferroni multiple comparison (χ2 = 212.204,d.f. = 3,P = 0.0001<0.01).