CAP-1 and CAP-2, but not CAP-3 are ligands for the Capa receptor (PubMed:12177421, PubMed:12459185). CAP-1 and CAP-2 are probably components of the signal transduction pathway that leads to Malpighian tubule fluid secretion via the second messenger nitric oxide (PubMed:11959669). CAP-3 is a ligand for the PK1-R G-protein coupled receptor (PubMed:16054112). Released from the neuroendocrine cells into the hemolymph. In larvae, the precursor peptide is exclusively present in a single pair of neuroendocrine cells in the labial neuromere (subesophageal ganglion) and three pairs of cells in the ventral ganglion abdominal neuromeres. Belongs to the pyrokinin family.