Abstract
The seasonal life cycle of the cabbage butterfly, Pieris melete is complicated because there are three options for pupal development: summer diapause, winter diapause, and nondiapause. In the present study, we tested the influence of temperature, day length, and seasonality on the expression of alternative developmental pathways and compared the differences in life history traits between diapausing and directly developing individuals under laboratory and field conditions. The expression of developmental pathway strongly depended on temperature, day length, and seasonality. Low temperatures induced almost all individuals to enter diapause regardless of day length; relatively high temperatures combined with intermediate and longer day lengths resulted in most individuals developing without diapause in the laboratory. The field data revealed that the degree of phenotypic plasticity in relation to developmental pathway was much higher in autumn than in spring. Directly developing individuals showed shorter development times and higher growth rates than did diapausing individuals. The pupal and adult weights for both diapausing and directly developing individuals gradually decreased as rearing temperature increased, with the diapausing individuals being slightly heavier than the directly developing individuals at each temperature. Female body weight was slightly lower than male body weight. The proportional weight losses from pupa to adult were almost the same in diapausing individuals and in directly developing individuals, suggesting that diapause did not affect weight loss at metamorphosis. Our results highlight the importance of the expression of alternative developmental pathways, which not only synchronizes this butterfly's development and reproduction with the growth seasons of the host plants but also exhibits the bet‐hedging tactic against unpredictable risks due to a dynamic environment.
Highlights
It has been clearly recognized that diapause is an important mechanisms for synchronizing seasonal development and activity in subtropical and temperate zone insects
We tested the influence of temperature, day length, and seasonality on the expression of alternative developmental pathways in P. melete under laboratory and field conditions and their differences in larval and pupal development time, pupal weight and growth rate, and adult weight and weight loss, aiming to understand how temperature, day length, and seasonality affect the evolution of their life‐history traits
Constant low temperatures of 16°C and the mean daily spring temperatures of 16.8 and 20.8°C combined with gradually increasing day lengths resulted in almost all individuals entering pupal diapause (98.2% and 97.1%)
Summary
It has been clearly recognized that diapause is an important mechanisms for synchronizing seasonal development and activity in subtropical and temperate zone insects. Pegomyia bicolor, 6 years of field observations indicated that 41%–70% of individuals that pupated during April 5–7 entered pupal diapause, while the rest continued to emerge and oviposit and produced the second generation (Xue, Zhu, & Shao, 2001). There are always some individuals entering winter diapause regardless of temperature, as indicated by the fact that 3.85% of individuals in 2003, 4.65% in 2004, and 6.78% of individuals in 2005 that hatched in August entered winter diapause even under high temperatures—from 26.4 to 31.2°C (Xiao et al, 2012) This insect species may serve as an excellent experimental model to test the differences in life history traits between the diapausing and directly developing individuals. We tested the influence of temperature, day length, and seasonality on the expression of alternative developmental pathways in P. melete under laboratory and field conditions and their differences in larval and pupal development time, pupal weight and growth rate, and adult weight and weight loss, aiming to understand how temperature, day length, and seasonality affect the evolution of their life‐history traits
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