BackgroundRibonucleosides and RNA are an underappreciated nutrient group essential duringDrosophilalarval development and growth. Detection of these nutrients requires at least one of the 6 closely related taste receptors encoded by theGr28genes, one of the most conserved insect taste receptor subfamilies.ObjectivesWe investigated whether blow fly larvae and mosquito larvae, which shared the last ancestor withDrosophilaabout 65 and 260 million years ago, respectively, can taste RNA and ribose. We also tested whether theGr28homologous genes of the mosquitoesAedes aegyptiandAnopheles gambiaecan sense these nutrients when expressed in transgenicDrosophilalarvae.MethodsTaste preference in blow flies was examined by adapting a 2-choice preference assay that has been well-established forDrosophilalarvae. For the mosquitoAedes aegypti, we developed a new 2-choice preference assay that accommodates the aquatic environment of these insect larvae. Finally, we identified Gr28 homologs in these species and expressed them inDrosophila melanogasterto determine their potential function as RNA receptors.ResultsLarvae of the blow flyCochliomyia macellariaandLucilia cuprinaare strongly attracted to RNA (0.5 mg/mL) in the 2-choice feeding assays (P< 0.05). Similarly, the mosquitoAedes aegyptilarvae showed a strong preference for RNA (2.5 mg/mL) in an aquatic 2-choice feeding assay. Moreover, when Gr28 homologs ofAedesorAnophelesmosquitoes are expressed in appetitive taste neurons ofDrosophila melanogasterlarvae lacking theirGr28genes, preference for RNA (0.5 mg/mL) and ribose (0.1 M) is rescued (P< 0.05).ConclusionsThe appetitive taste for RNA and ribonucleosides in insects emerged about 260 million years ago, the time mosquitoes and fruit flies diverged from their last common ancestor. Like sugar receptors, receptors for RNA have been highly conserved during insect evolution, suggesting that RNA is a critical nutrient for fast-growing insect larvae.