Presence of three diapauses in a subtropical cockroach: Control mechanisms and adaptive significance

Abstract

Diapause is common among insects and is regarded as an adaptive response to periodic occurrence of adverse conditions. It occurs at a particular developmental stage, typically only once in a lifetime. However, little is known about the details of the control mechanism of life cycles with multiple diapauses in insects. In this study, a complex 2-year life cycle with three types of diapause is reported in a subtropical cockroach, Symploce japonica: a winter diapause in mid-nymphal instars, a summer diapause in later nymphal instars, and a reproductive diapause is reported in the adult stage. Nymphal development was extremely slow either at short days (winter diapause) or long days (summer diapause). Nymphs in summer diapause matured rapidly when transferred from long days to short days, indicating that seasonal changes in day-length are the pivotal factor in the control of this life cycle. It is proposed that the main significance of winter diapause in this subtropical species is to enable the nymphs to survive the mild winter successfully with reduced energy demand, and that of summer diapause is to delay adult emergence until late in the autumn for successful induction of the following adult diapause. Adults do not emerge until shortly before winter, yet the presence of diapause in the adult stage does not simply appear to be a response to cope with the winter conditions but, instead, ensures that reproduction will occur early the next year, before summer, because reproduction is greatly hampered at high temperature.