Thermal factors affecting egg development in the wandering glider dragonfly, Pantala flavescens (Odonata: Libellulidae)

The wandering glider dragonfly, Pantala flavescens (Fabricius), arrives in Japan from tropical regions every spring. The offspring colonize areas throughout Japan, with rapid increases in populations in the autumn, but all individuals die in the winter, suggesting low tolerance to low temperatures. However, few quantitative data on egg development and water temperature have been reported for this species. Females at the reproductive stage were collected from fields throughout the flying season and their eggs released using an artificial oviposition technique. Almost all of the eggs were fertilized. Egg size was stable throughout the seasons. Most eggs hatched within a period of 5 days at high water temperatures (35 and 30 A degrees C), which were recorded in the shallow ponds and rice paddy fields from summer to early autumn. However, the egg-stage duration increased with declining water temperature. All eggs in water at 15 A degrees C had failed to hatch by 90 days. The calculated critical temperature of water was determined to be approximately 14.3 A degrees C; the total effective temperature for the egg stage was about 80 degree-days. Thus, low water temperatures in winter may prevent P. flavescens overwintering in Japan.