Gustatory receptor required for response to the bitter in taste neurons. Gr93a cells respond to bitter compounds such as caffeine. Flies avoid bitter substances, suggesting that Gr93a neuron activity is sufficient to mediate avoidance behavior. In larvae, is expressed in neurons of the dorsal pharyngeal sense organs. Disrupts fly aversion to caffeine. Belongs to the insect chemoreceptor superfamily. Gustatory receptor (GR) family. Gr93a subfamily.