Modulation of the temporal pattern of calling behavior of female Spodoptera littoralis by exposure to sex pheromone.

We have examined the timing of calling behavior in the female Egyptian cotton leafworm, Spodoptera littoralis and its modification by exposure to sex pheromone. The calling rhythm of the female moth was found to be circadian, persistent for at least 4 days once it has been entrained, and could be phase shifted by altering the light:dark regime. We also found that female exposure to pheromone affected the rate and duration of calling. A brief exposure to pheromone gland extract increased the proportion of females calling in a constant dim light and this effect persisted for at least 2 days. In response to pheromone exposure, significantly more females also called late into scotophase when most unexposed control females had ceased calling. The adaptive significance of responding to conspecific sex pheromone is discussed.

The circadian rhythm of the sex-pheromone-mediated behavioral response in the turnip moth, Agrotis segetum, is not controlled at the peripheral level.

The pheromone-mediated upwind flight of male turnip moths was observed in a flight tunnel at different times of day under conditions of a light-dark (LD) cycle, constant darkness (DD), and a shifted photoperiod. Under both LD and DD conditions, a significantly larger number of males flew to the pheromone during both the scotophase and the subjective scotophase than during the photophase and the subjective photophase for 2 consecutive days. When 1-day-old moths were transferred to a shifted LD cycle with lights turned off 4 h earlier, male behavioral responses to the pheromone advanced in time accordingly by 4 h. This showed that male behavioral responses to the pheromone are under the control of an endogenous oscillator. To further examine the level at which the circadian rhythm of the male behavioral response is regulated, the authors tested the olfactory responses of male antennal receptors to pheromone stimuli by means of electroantennograms (EAG) at different times of day. No significant variation in the sensitivity of the male antennal response to the pheromone was observed in terms of time of day. The results suggest that circadian regulation of the rhythmic behavioral response to pheromones in the male Agrotis occurs at the central nervous system level.