Abstract
The rice water weevil (RWW), Lissorhoptrus oryzophilus KUSCHEL, has widely infested paddy fields which are located at altitudes of 270 to 1, 200 m in Nagano Prefecture. The appearance and development of the RWW in the higher elevation area (alt. 1, 150 m) were observed ca. 10-20 days later than in the lower area (alt. 400 m). Population density was higher in the higher elevation area than in the lower one. Immigrant adults that were collected immediately after transplanting laid eggs at temperatures of higher than 20°C in the laboratory. Almost all eggs were laid in the first 2 weeks after the start of rearing at 20-30°C. It is considered that the temperature of a flooded paddy field is favourable for oviposition by immigrant adults, and that intensive oviposition by adults prevented a delay in the subsequent larval occurrence. There was no remarkable difference in survival rate from egg to adult emergence between the higher and lower elevation areas and mortality during the winter is not particularly high. It is, therefore, considered that the periods before entering hibernation in autumn and before immigration into the paddy field in spring are crucial for survival in the next generation.
