EFFECTS OF PHOTOPERIOD ON THE CIRCADIAN TIMING OF PHEROMONE RESPONSE IN MALE TRICHOPLUSIA NI - RELATIONSHIP TO THE MODULATORY ACTION OF OCTOPAMINE

The pheromone-mediated upwind flight of male cabbage looper moths was measured through-out the scotophase in a series of photoperiods, to de termine the phase-relationship between the time of peak response to ph eromone during the dark and the photoperiod cues, Male upwind flight a nd source contact was measured to a low dose of pheromone, one that wo uld best reveal the presence of a temporal peak in male sensitivity, R esults failed to support the idea that there is a narrow 'window' of m aximal sensitivity during the dark that is phase-regulated by either t he lights off, or lights on signal, Rather, there was a clear relation ship between the lights off signal and the time (2-3h) to reach maxima l response levels, regardless of the duration of the dark, Once the po int of maximal response was reached, response levels displayed relativ ely constant levels until the very end of the dark period, Experiments involving shifts in the time of lights off or lights on also supporte d the idea that the lights off cue is critical for expression and timi ng of the response rhythm, Other experiments confirmed that a circadia n oscillator is involved, evidenced by the rhythmic expression of male behavior mirroring the duration of expected dark periods in two photo periods when males were tested in constant dark conditions, Also, cons tant dark and light conditions significantly affected the pattern of c hange in levels of octopamine observed in the brain in a light:dark re gime, Of particular interest, the pattern of decrease in octopamine le vels correlated well with the pattern of response to sex pheromone ove r the dark, supporting an earlier hypothesis that octopamine modulates neural pathways involved in perception of the odor signal, and that t his action is triggered by the lights off cue, The results support the conclusion that the lights off photoperiod cue is a critical time in which a number of physiological process are initiated that will affect male response thresholds for a number of behaviors during the dark, i ncluding our previously demonstrated modulatory action of octopamine o n the sensitivity of male moths to sex pheromone. Copyright (C) 1996 E lsevier Science Ltd