Timing of life cycles in a seasonal environment: the temperature-dependence of embryogenesis and diapause in a grasshopper (Chorthippus brunneus Thunberg).

The durations of the stages in the embryonic development of Chorthippus brunneus (Thunberg) have been estimated at constant temperatures of 20° C and 30° C. There was stage-dependent variation in the temperaturedependence of morphogenesis-a pattern apparently not previously described. The earliest and latest stages of morphogenesis proceeded relatively rapidly at higher temperatures. But intermediate stages, which would tend to occur around the diapause stage in a temperate winter, proceeded relatively rapidly at lower temperatures, as did diapause development. At a given temperature, there was individual variation between eggs such that some developed consistently faster than others. However, these intrinsic differences could be altered by exposure to diapause-breaking conditions at different morphological stages. The results are discussed in terms of their adaptive significance, their effect on population dynamics in a seasonal environment, and their implications for the nature of diapause in insects generally.