Gustatory receptor which mediates acceptance or avoidance behavior, depending on its substrates. Gr43a is the main sugar receptor in larvae. Functions as a narrowly tuned fructose receptor in taste neurons but also as a fructose receptor in the brain. Necessary and sufficient to sense hemolymph fructose and promote feeding in hungry flies but suppress feeding in satiated flies. Expressed in the adult labellar chemosensory neurons and in the adult head, abdomen, leg and wing. In larvae, is expressed in taste organs, as well as the brain and the gastrointestinal system. Belongs to the insect chemoreceptor superfamily. Gustatory receptor (GR) family. Gr21a subfamily.