REGIONAL CONTROL THRESHOLD OF RICE STEM B ORER, CHILO-SUPPRESSALIS WALKER (LEPIDOPTERA, PYRALIDAE), INDICATED BY ADULT CATCH WITH SEX-PHEROMONE TRAP

The number of overwintering Chile suppressalis Walker moths caught by a sex-pheromone trap and the proportions of rice plants injured by fir st-generation larvae were investigated in three regions (300, 600, 1,5 00 hectares) with different topographies in Niigata Prefecture. A sign ificant linear relationship was found between the lumber of moths caug ht by the sex-pheromone traps and the number of injured plants. The to tal number of caught moths could be estimated by the number of moths c aught up to 10 June, 1 to 2 weeks before the best time for insecticide application. The control threshold level for the first generation cau ght by a sex-pheromone trap was 800 moths per trap up to 10 June based on established control threshold levels indicated by withered leaf sh eaths in Niigata Prefecture. About 10 traps per region were needed to estimate the mean catches per trap with 10-20% error.