Analysis of Some Biological Factors Affecting Differential Pheromone Trap Efficiency between Generations in the Rice Stem Borer Moth, Chilo suppressalis(WALKER)(Lepidoptera:Pyralidae)

Pheromone trap efficiencies in C. suppressalis tend to be relatively low in the first generation as compared to those of the overwintered generation. In order to clarify the factors affecting this phenomenon, three possible biological aspects, such as the male pheromone responsiveness, the flight ability of male moths, and the effect of female population densities were compared between the two generations. The responses of male moths to varying doses of the synthetic sex pheromone were not significantly different between the two generations for each concentration. No significant differences in the flight ability (duration, distance, sped) between the two generations were found. Significant declines in pheromone trap catches with increasing female population densities, evaluated by the light trap catches, were detected in both generations. However, the effects of the female population density were apparently greater in the first generation than in the overwintered one. Consequently, the female population density in the paddy fields was thought to be one of the critical factors affecting the difference in pheromone trap performance between the two generations.