One year ago, we discovered a new family of insect RYamide neuropeptides, which has the C-terminal consensus sequence FFXXXRYamide, and which is widely occurring in most insects, including the fruitfly Drosophila melanogaster and the red flour beetle Tribolium castaneum (F. Hauser et al., J. Proteome Res. 9 (2010) 5296-5310). Here, we identify a Drosophila G-protein-coupled receptor (GPCR) coded for by gene CG5811 and its Tribolium GPCR ortholog as insect RYamide receptors. The Drosophila RYamide receptor is equally well activated (EC(50), 1 x 10(-9) M) by the two Drosophila RYamide neuropeptides: RYamide-1 (PVFFVASRYamide) and RYamide-2 (NEHFFLGSRYamide), both contained in a preprohormone coded for by gene CG40733. The Tribolium receptor shows a somewhat higher affinity to Tribolium RYamide-2 (ADAFFLGPRYamide; EC(50), 5 x 10(-9) M) than to Tribolium RYamide-1 (VQNLATFKTMMRYamide; EC(50), 7 x 10(-8) M), which might be due to the fact that the last peptide does not completely follow the RYamide consensus sequence rule. There are other neuropeptides in insects that have similar C-terminal sequences (RWamide or RFamide), such as the FMRFamides, sulfakinins, myosuppressins, neuropeptides F, and the various short neuropeptides F. Amazingly, these neuropeptides show no cross-reactivity to the Tribolium RYamide receptor, while the Drosophila RYamide receptor is only very slightly activated by high concentrations (>10(-6) M) of neuropeptide F and short neuropeptide F-1, showing that the two RYamide receptors are quite specific for activation by insect RYamides, and that the sequence FFXXXRYamide is needed for effective insect RYamide receptor activation. Phylogenetic tree analyses and other amino acid sequence comparisons show that the insect RYamide receptors are not closely related to any other known insect or invertebrate/vertebrate receptors, including mammalian neuropeptide Y and insect neuropeptide F and short neuropeptide F receptors. Gene expression data published in Flybase (www.flybase.org) show that the Drosophila CG5811 gene is significantly expressed in the hindgut of adult flies, suggesting a role of insect RYamides in digestion or water reabsorption. (C) 2011 Elsevier Inc. All rights reserved.