Male Catches of Spodoptera litura (F.) in Pheromone Traps under Fluctuating Wind Velocity : Validity of the Active Space Model

Abstract

In order to know whether the "active space model" for male orientation to a pheromone source, which was developed by NAKAMURA and KAWASAKI (1977), can be applied to a situation of fluctuating wind conditions during short periods Spodoptera litura male catches in a pheromone trap during 10 min periods were analyzed. Males did not come continuously to the trap but did come intermittently, the longest period when none were attracted being during 5 or 6 min. The wind velocity changed from a high to a low level during these periods.The active space model was modified to apply to a situation of fluctuating wind velocity, and catches obtained experimentally from different release points from the trap were compared with those obtained from a computer simulation using this model. In more than half the cases experimental results differed significantly from the simulated results. Thus, the active space model, which does not describe instantaneous pheromone behaviour, is not really applicable to fluctuating wind conditions during short periods. However, the distance within which released males were captured in the trap was not greatly different between experimental and simulated results except at the time of weak wind. These facts led to the conclusion that this model is valuable in representing the "time-average" active space (or pheromone plumes) during a certain period.