The circadian rhythm of flight activity of Spodoptera exigua males in response to sex pheromone

In many moths, male attraction to the blend of synthetic sex pheromone releasing continuously in the field shows an apparent circadian rhythm similar to that of locomotion activity. In this study, the daily rhythms of electroantennography (EAG) and behavioral responses to sex pheromone, and the daily rhythms of locomotion activity were measured in male beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). The peaks of males trapped by light and sex pheromone were all during the latter part of the night in the field. However, there was no significant variation among time intervals in the EAG responses of male antennae to sex pheromone stimuli. The principal period of locomotion activity under L15:D9 (LD) continued to occur during the scotophase and the subjective scotophase in the day of constant darkness (DD1) and the second of two consecutive days of constant darkness (DD2). The majority of males contacted the sex pheromone source in a wind tunnel during the latter part of the scotophase under LD and the subjective scotophase for DD1 and DD2. There were significant associations between the rhythm of the behavioral response to sex pheromone and locomotion activity. These results suggested that the male's behavioral response to sex pheromone in the beet armyworm could be observed only until locomotion activity of the male occurred at the end of the dark period, despite sex pheromone being released continuously from synthetic pheromone‐baited traps in the field.