Abstract
In 1967, the adult immigration period of the first generation, estimated by the yellow pan water traps, began from about May 20 and continued until about June 20, showing several minor peaks, in seedling beds and early transplanted paddy fields (Fig.1). In the ordinary transplanted fields immigrants were found from the end of June to mid july, which seemed to be the emergence period of the second generation.
Infection by the rice stripe virus was severe in the fields transplanted within May (Table 1).
Percentage of infective planthopper tested by the anti-body sensitized hemagglutination method of the first generation collected from 13 wheat fields in Chikugo was 7.45% (313/4199) in average, the lowest being 3.75% and the highest 10.24%. Those of adults collected in 9 rice seedling beds was 7.24% (224/3096), the lowest 5.88% and the highest 8.26%, very much similar to those obtained from wheat fields (Table 2 and 3).
In a paddy field transplanted on 19 May, symptoms of RSV appeared from the beginning of July and reached to maximum in August, over 60% of plants being infected. Percentage of infective plant hopper increased along with the increase of infected rice plant with about a half month's lag, reaching nearly 50 %, though the density of planthopper was extremely low.
Percentage of infective planthopper of overwintering generation was traced from the beginning of December to April. No consistent seasonal fluctuation of the percentage was found; being 5.77% in average (117/2026).
