[01] Shigeru Kikukawa, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan. [02] Shin Katou, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan. [03] Takamasa Matsuda, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan. [04] Akitoshi Miyashita, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan. [05] Tarou Tsuzuki, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan.

The Indian meal moth, Plodia interpunctella Hübner (Lepidoptera: Pyralidae), may diapause as a last (5^th) instar larva in response to the preceding photoperiod. At 25°C, light intensities above 200μW/cm² (daylight fluorescence at c. 400-750 nm) on the surface of the larval diet prevented diapause in a long day of LD 16:8 h (L=light and D=dark) and induced it in a short day of LD 12:12 h. Blue (400-495 nm), green (505-575 nm) or red (610-750 nm) filtered light at 200μW/cm² prevented and induced diapause in LD 16:8 h and LD 12:12 h, respectively. In another experiment, larvae were exposed to LD 16:8 h but for 4-h light period after light-on (dawn) or before light-off (dusk) were kept at different wavelengths (i.e., blue, green or red) maintained at 200μW/cm². If the larvae are insensitive to colored light, the effective photoperiod will be 12 h and diapause will be induced. Most of the larvae averted diapause, indicating that they were wavelength-sensitive in early or late scotophase. Next, the midnight of LD 12:12 h was interrupted with a 2-h light pulse of the different wavelengths at intensities of 100, 200 and 300μW/cm². Interrupting the scotophase by >200μW/cm² light prevented diapause at all wavelengths, indicating that diapause in this insect is determined by a wide range of the visible spectrum.

Indian Meal Moth, Larval Diapause, Light Intensity, Wavelength, Spectral Sensitivity

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