To discriminate between these possibilities, we played white noise to a male in the presence of a decapitated silent female. White noise was equipotent in stimulating initiation, indicating that mechanosensory signals are likely to act by increasing the males state of alertness instead of being recognized as specific indicators of the presence or location of another fly. TNT/Gr68a mutant males showed a defect in finding active females and a delay in courtship initiation in dark conditions. Gr68a-GAL4 is pleiotropically expressed in many parts of fly body. Which Gr68a-positive cells are responsible for the female detection? One of the strongest areas of Gr68a-GAL4 expression is found in Johnston��s organ, the main auditory organ for detection of wing-vibrating courtship song. The song signal is first sensed by an arista attached on the third segment of antenna then transmitted to Johnston��s organ inside the second segment. In Drosophila melanogaster, fruitless, a sex-determination transcription factor, is expressed in most of the auditory neurons of Johnston��s organ, implying that audition plays an important role in sexual behavior. When a female is exposed to conspecific courtship song, she reduces her locomotion to accept copulation. On the other hand, a male, listening to the courtship song of other males nearby, increases his locomotion and performs enhanced courtship. In order to examine whether males use the arista-Johnston��s organ auditory system to detect the moving-female signal, we measured courtship behavior of an auditory mutant, 5D10, and found a defect in courtship initiation in the dark, with a mean latency of 5536185 sec, which was significantly lower than that of its genetic control line, 40A-G13, supporting a role of the auditory system in courtship initiation. We also surgically manipulated arista function and compared courtship responses to those of intact males. Aristae of wild-type males were either fixed to the third MK-2206 antennal segment with a small amount of wax or partially amputated with fine scissors. The males with waxed-arista showed a significantly longer latency of courtship initiation than intact males courting intact females. The level corresponded to that of intact males courting decapitated silent females. This was consistent with a freely moving arista being essential for the female-movement detection. However, in this manipulation, the wax also AMN107 covered some surface area of the third antennal segment so that it is possible that olfactory function was also disrupted, which may cause delayed courtship initiation. Therefore, we next cut most of both aristae off with fine scissors.