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 l ow in the first generation as compared to those of the overwintered ge neration. In order to clarify the factors affecting this phenomenon, t hree possible biological aspects, such as the male pheromone responsiv eness, the flight ability of male moths, and the effect of female popu lation densities were compared between the two generations. The respon ses of male moths to varying doses of the synthetic sex pheromone were not significantly different between the two generations for each conc entration. No significant differences in the flight ability (duration, distance, speed) between the two generations were found. Significant declines in pheromone trap catches with increasing female population d ensities, evaluated by the light trap catches, were detected in both g enerations. However, the effects of the female population density were apparently greater in the first generation than in the overwintered o ne. Consequently, the female population density in the paddy fields wa s thought to be one of the critical factors affecting the difference i n pheromone trap performance between the two generations.