Peripheral coupling between Ca²⁺ dynamics and neural output in tarsal gustatory sensilla of Bactrocera dorsalis

The oriental fruit fly, Bactrocera dorsalis (Hendel), depends on peripheral gustation for feeding decisions and host assessment, yet the physiological coupling between early sensory transduction and downstream behavioral output remains poorly resolved. Here, we investigated the physiological responses of mid-tarsal gustatory sensilla in mated females using non-invasive micro-test technology (NMT) to quantify real-time Ca²⁺ flux, single-sensillum recording (SSR) to measure neuronal activity, and proboscis extension response (PER) assays to evaluate feeding behavior. Upon stimulation with ecologically relevant phagostimulants (fructose and sucrose) and deterrents (L-nicotine and tannic acid), we found that all tastants induced measurable Ca²⁺ influx, but their downstream coupling among ionic, electrophysiological, and behavioral layers differed substantially. Fructose stimulation generally elicited close correspondence among Ca²⁺ influx, spike activity, and feeding responses, whereas sucrose exhibited partial dissociation at elevated concentrations. In contrast, deterrent stimuli produced pronounced functional uncoupling: sustained Ca²⁺ influx persisted even when spike output was strongly suppressed under high-intensity stimulation. The PER of B. dorsalis under deterrent stimulation was more closely associated with persistent ionic signaling than with spike frequency alone. These findings indicate that the tarsal sensilla of B. dorsalis function not simply as passive detectors, but as early peripheral sensory checkpoints in which tastant-specific coupling and uncoupling among ionic, electrophysiological, and behavioral layers shape early feeding decisions.