Effects of photoregime on the diel rhythmicity of male responses to sex pheromones in Glyphodes perspectalis (Lepidoptera: Crambidae)

Abstract

We examined the effect of the photoregime on the timing of male responsiveness to sex pheromones in the box tree pyralid, Glyphodes perspectalis. Circadian oscillation was observed in the male responsiveness of G. perspectalis, evidenced by the rhythmic expression of male responsiveness in the duration corresponding to the expected scotophase of the continuous light or continuous dark conditions, when males reared under 16L8D were transferred to continuous light or continuous dark conditions. When male responsiveness to the sex pheromone was measured throughout the scotophase under three different photoregimes, it was shown that the time to reach the maximal response after lights-off was rather constant (approximately 2 h), regardless of the duration of the scotophase in three cases of 6, 8 and 10 h. The maximal response in the three cases appeared to be maintained until the end of the scotophase. Furthermore, in an experiment involving ±2-h shifts of lights-on or -off from the usual 16L8D, male responsiveness peaked within 2 hafter lights-off, and persisted throughout the remaining dark period. These results suggest that, at least under the present experimental conditions, the diel rhythmicity of male responsiveness based on the endogenous circadian rhythm is coordinated by the light-dark regime, and lights-off cues are critical for the timing and expression of the response rhythm leading to increased responsiveness.