Ligand for the neuropeptide SIFamide receptor (PubMed:16378592). Modulates sexual behavior by negatively regulating female receptivity to male courtship and by playing a role in male sex discrimination (PubMed:17126293, PubMed:26469541). Also involved in promoting sleep (PubMed:24658384). Strongly expressed in two pairs of neurons in the pars intercerebralis (at protein level). RNAi-mediated knockdown in SIFa-expressing neurons causes normal male sexual activity towards virgin females but also vigorous courtship directed at other males and also leads to female hyper-receptivity with a dramatic decrease in copulation time (PubMed:17126293). It also causes reduced sleep and shortened sleep bout length (PubMed:24658384). Belongs to the FARP (FMRFamide related peptide) family. Probably cloning artifact. Extended N-terminus. Extended N-terminus. Extended N-terminus.