Effects of photoperiod and temperature on development and reproduction of Hydromedion sparsutum (Müller) (Coleoptera, Perimylopidae) from South Georgia (Subantarctic).

1. Under laboratory conditions complete development of H. sparsutum is shown within a temperature range of-0.7°C to +8°C. Constant temperatures above 10°C are lethal to the population. Larval growth (L1 to L5) is strictly temperature-dependent between-0.7 and +3.5°C, but slightly temperature compensated between +3.5 and +8°C. 2. Rate of egg production is highest at an average daily temperature of-0.7°C. 3. The sixth larval stage (L6) can be subdivided into a wandering and feeding period of about 40 days (at 7.3°C) and a following prepupal resting stage (PPR) with a high variability in duration, even at one and the same temperature, which ends with pupation. 4. Entrance into this resting stage seems to be independent of environmental changes and can occur at every time of the year. Termination of the PPR depends upon light stimuli received during the entire larval period. 5. Readiness for pupation exists when the photoperiod in the PPR exceeds that during hatching of first larva. A decreasing photoperiod during PPR triggers pupation in prepupae of various age. 6. The diapause stage seems to be a primary factor synchronizing the life cycle with seasonal changes in the environment.