Abstract
The number of overwintering Chilo suppressalis WALKER moths caught by a sex-pheromone trap and the proportions of rice plants injured by first-generation larvae were investigated in three regions (300, 600, 1, 500 hectares) with different topographies in Niigata Prefecture. A significant linear relationship was found between the number of moths caught by the sex-pheromone traps and the number of injured plants. The total number of caught moths could be estimated by the number of moths caught up to 10 June, 1 to 2 weeks before the best time for insecticide application. The control threshold level for the first generation caught by a sex-pheromone trap was 800 moths per trap up to 10 June based on established control threshold levels indicated by withered leaf sheaths in Niigata Prefecture. About 10 traps per region were needed to estimate the mean catches per trap with 10-20% error.
