Dsx-dependent essential component of pheromone-driven courtship behavior (PubMed:12971900). Recognizes a female pheromone involved in the second step (tapping step) of the courtship display which is essential for efficient execution of the entire courtship sequence and timely mating (PubMed:12971900). Required for detection of the male sex pheromone CH503 which is transferred from males to females during mating and inhibits courtship behavior by other males (PubMed:26083710). Gr68a-expressing neurons in the male foreleg relay signals to the suboesophageal zone (SEZ) and courtship suppression is mediated by the release of the neuropeptide tachykinin from a cluster of 8-10 neurons in the SEZ (PubMed:26083710). Expressed in chemosensory neurons of about 20 male-specific gustatory bristles in the forelegs (PubMed:12971900). No expression is seen in the mechanosensory neurons (PubMed:12971900). In larvae, expressed in the ventral pharyngeal sense organ (PubMed:22031876). Mutant males display robust courtship behavior in the presence of CH503-perfumed females. Belongs to the insect chemoreceptor superfamily. Gustatory receptor (GR) family. Gr21a subfamily.