The roles of temperature and diapause in the life history of a temperate‐zone dragonfly: Argia vivida (Odonata: Coenagrionidae)

. 1. The life cycle of Argia vivida Hagen generally took longer to complete in the field than was predicted on the basis of the thermal sum accumulated in laboratory rearing. 2. The prediction of a bivoltine life‐cycle from geothermal sites with either a constant annual temperature of 26°C or thermal range of 11–31°C was not borne out because the intervention of short‐day induced developmental delays in later larval instars extended the life cycle to 1 year. 3. This diapause, which synchronizes adult emergence with favourable summer temperatures, was also present in larvae from sites with annual temperature ranges of 0–33°C and 5–20°C. 4. At these colder sites completion of the life cycle takes 2 and 3 years respectively and dragonflies must be in cold‐resistant stages during the winter. A long‐day diapause, principally affecting late‐instar larvae below a certain size during the summer, achieves this. 5. Large diurnal temperature fluctuations at the 0–33°C site markedly increase the useful thermal energy available to larvae for growth over that predicted by the thermal sum equation. 6. The interaction between the effects of temperatures favourable for growth and day‐length‐governed diapause, synchronize the emergence of the low‐temperature sensitive adult stage of this tropical dragonfly with northern‐latitude summers at a variety of habitats.