Oviposition date and pattern of embryogenesis in the grasshopper Chorthippus brunneus (Orthoptera, Acrididae)

The morphological development of eggs of the grasshopper Chorthippus brunneus , laid during successive periods through a single season, was closely monitored in the field at a site in NW England. Eggs within the same clutch developed synchronously. However, there were significant differences between clutches laid at the same time, reflecting spatial variation in microclimate (and possibly maternal effects and/or genetic differences). Eggs laid early in the season entered diapause and hatched relatively synchronously in the following spring. Eggs laid later failed to reach the diapause‐stage before winter, but hatched, albeit late and with greater variance. Diapause was averted in these eggs. Plasticity in the nature of diapause has been documented from laboratory studies of many insect species (including C. brunneus ,) but this study directly relates the incidence of such developmental plasticity to oviposition date and seasonal temperature cycles in the field. The adaptive significance of diapause aversion and the evolutionary consequences for female reproductive behaviour are considered.