Females of Blattella germanica feed compulsively on a nuptial secretion from the male's eighth tergal gland (TG-8) during courtship. Using TG-8 extract and its essential ingredients, maltotriose (MT) and 1,2-dioleoylphosphatidylcholine (PC), we investigated the perception of the secretion by gustatory sensilla in both sexes. Female-biased chemosensitivity was found in the feeding responses to the TG-8 extract. The TG-8 extract induced specific impulses in four functionally different receptor cells: the sugar, salt and other two types of receptor cells in a single gustatory sensillum on the paraglossae in both sexes. The impulse frequencies of the sugar receptor cell and a receptor cell of unknown type were significantly higher in females than those in males. There were no sexual differences in the behavioral and electrophysiological responses to MT alone; no responses were elicited by PC. However, a mixture of MT and PC elicited the behavioral responses more strongly than MT in females. The impulse frequency of sugar receptor cells toward the mixture of MT and PC also increased in females but not in males. These results suggest that the synergistic effect of PC on 'sweetness' of MT in the female cockroach contributes to her compulsive nuptial feeding. The female-biased gustatory sensitivity seems to ensure successful coupling during the nuptial feeding.