Abstract
In order to forecast the dispersal period of the adults of the rice water weevil from overwintering sites to paddy fields, the temperature dependence of the flight muscle (epipleural muscle) development and flight activity was investigated. The threshold temperature for development of the flight muscle was 13.8°C. When the adults which were collected in woodlands in early spring were reared without food, the flight muscle showed only a little development. Fully developed flight muscles degenerated remarkably from 12 to 18 days after starvation. The overwintered adults started to fly from 6 to 8 days, and 50% of the adults from 9 to 12 days after rearing respectively. The relationship between the cumulative percentage of flying adults and effective cumulative temperature was represented by an equation. When the adults with developed flight muscles were kept in each plastic cup at different temperatures, the rates of adults flying out from the cups were very high at 25°C and 27.5°C, and the rates of flying adults decreased at 30°C and 22.5°C. But at 20°C the rate of flying adults was very low, and at 18.5°C no flying adults were observed. The period when adults which had overwintered migrated from bamboo grasses in the woodlands coincided precisely with the simulated period of flight initiation in the adults.
