Insect odorant receptors (ORs) are a family of chemoreceptors activated by volatile chemicals. ORs form heteromeric complexes, believed to function as non-selective cation channels, comprising an OR and the co-receptor Orco. ORs are expressed in the dendrites of subsets of olfactory neurons in the antenna and maxillary palp. (Adapted from FBrf0168007 and FBrf0220463).