Gustatory receptors in Lepidoptera: chemosensation and beyond

Lepidoptera is one of the most widespread insect orders and includes several agriculturally important insect species. Ecological success of the lepidopteran insects partly depends on their adaptive chemoreception tactics, which play an important role in the selection of hosts, egg-laying sites and mates. Members of the G-protein coupled receptor family, gustatory receptors (GRs), are an integral part of the Lepidoptera chemosensory machinery. They are expressed in chemosensory neurones and are known to detect different environmental stimuli. Here, we discuss various aspects of the lepidopteran GRs with an emphasis on their roles in different processes such as chemosensation, host selection and adaptation. Phylogenetic analyses have shown that the large diversity of GR genes may have been generated through gene duplication and positive selection events, which also show lineage-and tissue-specific expression. Moreover, lepidopteran GR proteins are diverse and demonstrate broad ligand selectivity for several molecules including sugars, deterrents, salts and CO2. Binding of ligands to GRs generates multiple downstream changes at the cellular level, which are followed by changes in behaviour. GRs play a critical role in chemosensation and influence the insect's behaviour. Overall, insect GRs are potential targets in the design of effective insect control strategies.