Abstract: Suppressing effects of mass trapping using synthetic sex pheromone with main active ingredients of Z-11hexadecenal, Z-13 octadecenal and Z-9-hexadecenal on the rice stem borer, Chilo suppressalis were investigated during the flight periods of the overwintering and 1st generation in the paddy area of 60 ha in 1999. Population density of C. suppressalis in the pheromonetreated fields was lower than that in control. The egg masses decreased by 74.39% and population size of adult males of the 1stgeneration decreased by 61.64% in the treated fields as compared to control. Meanwhile, the damage by C. suppressalislarvae was significantly lower in the treated fields than control (ttest, P=0.05). Percentages of brownish leaf sheath, dead heart, and white head in the treated fields were decreased by 70.90%, 57.01% and 44.30%, respectively in contrast to control. The present study demonstrated that mass trapping to C. suppressalis using synthetic sex pheromone shows great potential as an alternative measure in an environmentfriendly pest management and at the same challenging the insecticide use that has some environment impacts.

Key words: Chilo suppressalis, sex pheromone, mass trapping, rice