Sweet and bitter compounds excite different sensory cells and drive opposing behaviors. It is commonly thought that the neural circuits linking taste sensation to behavior conform to a labeled-line architecture, but in Drosophila, evidence for labeled lines beyond first-order neurons is lacking. To address this, we devised trans-Tango(activity), a strategy for calcium imaging of second-order gustatory projection neurons based on trans-Tango, a genetic transsynaptic tracing technique. We found distinct projection neuron populations that respond to sweet and bitter tastants. However, the bitter-responsive population was also activated by water alone. We further discovered that bitter tastants evoke activity upon both stimulus onset and offset. Bitter offset responses are exhibited by both first- and second-order gustatory neurons, but these responses are distributed among multiple types of projection neurons in the second order. These findings suggest a more complex coding scheme for gustatory information than can be explained by a labeled line model.