Synoptic weather conditions inducing long-distance immigration of planthoppers, Sogatella furcifera Horvath and Nilaparvata lugens Stal
Entomology Laboratory, The Central Agricultural Experiment Station, Ministry of Agriculture and Forestry, Konosu, Saitama, Japan 365.
- 1Adults and nymphs of Sogatella furcifera and Nilaparvata lugens are serious pests of growing rice in Japan. They appear in June and July but their origin was unknown. Inflow of warm and humid air from the south was shown to favour the appearance of planthoppers. The air inflow was associated with the passage of depressions along the frontal zone, called Bai-u in the Far East.
- 2Immigrations were categorized as mass or minor according to the density of immigrants surveyed by various traps. The mass immigrations were induced by the passage of depressions which emerged in the central part of the Chinese continent between 25 °N and 35 °N and proceeded eastwards between the observation point and about 600 km north. Warm and humid south west winds blew, on average, for 19.3 h at an average wind speed of 32.9 km/h. When the route digressed a little north or south, minor immigrations, with only S.furcifera in half the cases, occurred.
- 3Minor immigration types were categorized into a long-lasting type which appeared in the final stage of the rainy season, a mass immigration typemodified by the location of a typhoon in the south, and a minor type near the frontal line occurring without the passage of recognizable depressions.
- 4The greatest aerial densities of immigrants were estimated as three to seven per 103m3 in S.furcifera and one to two per 103 m3 in N.Iugens. Female immigrants were mostly unmated.
- 5All the depressions that appeared in June and July 1967–72 were analysed and twenty-nine (76.3%) out of thirty-eight originating in the central part of the Chinese continent, caused immigrations. Yearly fluctuations of planthopper infestations in Japan were shown to depend on the yearly fluctuations of the route of depressions associated with the migration of the planthoppers.