Rice planthoppers are major pest for rice plants in Asian countries. They immigrates from overseas to Kyushu in Japan in the Baiu season every year. To predict the long distance migration of rice planthoppers to northern Kyushu, a migration model was developed with a hypothesis that rice planthoppers were transported by low-level jet stream at 1,000-2,000 m heights. The weather conditions for the migration period (June to July) were analyzed with the 850 mb chart at 21 h in 1980-1985 and at 09 h and 21 h in 1986, and possible migration days were decided. On the other hand, actual migration flight waves were decided with the number of catches by two nets. The possible migration flights decided by the weather chart agreed approximately with the actual flights. The accuracy of this prediction method was improved by using the 850 mb chart at 09 h additionaly. Finally, the prediction procedure was described.

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A population of green rice leafhopper, Nephotettix cincticeps Uhler (GRH), was artificially selected on 5 resistant rice varieties in the laboratory. The GRH lines selected on Saikai 164, Saikai 182, and Kanto-PL 6 were able to survive and reproduce on their respective varieties. In these lines, the developmental period of nymphs was shortened by continuous selection, although in the first generation it was longer than that of the line reared on Nipponbare carrying no resistance gene. We could not establish GRH lines virulent to Norin-PL 5 or Norin-PL 6. Six lines, reared on IR 24, Chugoku 105, Saikai 164, Saikai 182, Kanto-PL 6, and Aichi 80, were assessed for virulence among different resistant varieties by conducting a seedling test. All lines were highly virulent to the varieties on which they were selected. Similar virulence was obtained for combinations of IR 24 and Chugoku 105 lines, Saikai 164 and Saikai 182 lines, and Kanto-PL 6 and Aichi 80 lines. The Kanto-PL 6 and Aichi 80 lines were moderately virulent to Tadukan and Rantaj-emas 2. No lines were virulent to Norin-PL 5, Norin-PL 6, and Pe-bi-hun. The results of the leaf blade test were similar to those of the seedling test. The allele test confirmed that the GRH-resistance genes of Kanto-PL 6 and Aichi 80 are the same, and the resistance gene of Norin-PL 2 is located at a different locus from that of Kanto-PL 6 and Aichi 80. These results suggest that the virulence of GRH biotypes corresponds to the resistance genes of rice varieties and therefore, the use of biotypes allows the identification of groups of rice varieties that have similar resistance genes. We propose that the biotypes virulent to Grh 1-, Grh 2-, and Grh 3 (t)-carrying varieties be designated "Biotype 1", "Biotype 2", and "Biotype 3", respectively.