A rotary illumination method has been applied for controlling the fruit-piercing moths in orchards. The optimum rotary speed of the light source, however, remains undetermined from the phoro-adaptative physiology of the compound eye in nocturnally active moths. The photo-adaptative phenomenon of the retinula pigments in the silkworm moth eye were examined using the migration-index (YAGI and KOYAMA, 1963b). Such results were obtained as the shorter the alternation time of light-dark became, the more the effect of darkness was reduced, and finally the migration-index approached the value of complete light adaptation. Therefore, the photic-condition was considered to be continuous illimination, when the light source was rotated with a speed of less than one minute per rotation, which was practically demonstrated in the present experiment.