No Longer Forgotten: Pupation as a Critical Link in the Lepidopteran Life Cycle

Abstract

Holometabolous insects, those that undergo complete metamorphosis, owe their tremendous evolutionary success in large part to an efficient division of labor between a larval phase that focuses on feeding, and an adult phase specialized to reproduce and disperse. As the locus of the dramatic transition between these two distinct morphologies, the pupal phase is a critical link in the life cycle -- and yet it is poorly understood, in part because this vulnerable and often cryptic life stage has evolved to take place out of sight of potential natural enemies (including human observers). In my dissertation, I examine a number of different aspects of the pre-pupal and pupal phases of the lepidopteran life cycle. In Chapter 1, I review the published work on ecological studies of pre-pupal behavior, pupation, and pupal survival. In Chapter 2, I use manipulative experiments in the laboratory to investigate the sensory cues and behaviors used by pre-pupal Epargyreus clarus (Lepidoptera: Hesperiidae) larvae to navigate to a location for the pupal phase. In Chapter 3, I use field-based experiments and monitoring to investigate natural pupal mortality, comparing survival in direct-developing summer pupae and diapausing overwintering pupae. In Chapter 4, I report on the effect on E. clarus pupae of extended summers and heat waves, simulated in the laboratory, comparing their body composition with pupae that experienced milder heat treatments. Finally, in Chapter 5, I examine the effect of human-impacted environments on the pupal phase, first in a study of the ability of pre-pupal larvae to burrow into compacted soils, and then in a survey exploring the current attitudes and practices of butterfly garden managers relating to insect pupae. Together, these studies significantly increase our understanding of the pupal phase of Lepidoptera, and will enhance our ability to conserve holometabolous species.