Taste response profiles of the labellar chemosensilla of the medfly Ceratitis capitata (Diptera: Tephritidae).

The medfly (Ceratitis capitata Wiedemann, 1824) is a widespread pest for horticulture, mainly targeting fruits of pomaceous and citrus cultivars. Scanty data is available about its chemosensory responses to contact salty, sweet, sour and bitter stimuli. Hight Resolution Scanning Electron Microscopy (HRSEM) and Trasmission Electron Microscopy (TEM)observation indicate the presence of six pairs of Long type and about 40 pairs of Intermediate type labellar chemosensilla, each containing four different neurons. Spike activity was electrophysiologically recorded from the labellar sensilla in response to sodium chloride (NaCl), fructose, acids (citric and malic) and bitter compounds (quinine, quercetin and 6-n-propyl-thiouracil (PROP). By analysis of spike waveforms in the responses, four neurons were identified responding to different stimuli in both sensillum types of C. capitata. The response specificity of three of these cells (named M1, M2 and S) was 15 determined on the basis of their dose-response profiles. “M1” was specific to NaCl, “M2” to fructose. Both acids appeared to excite the “S” cell and to inhibit the “M1” cell. Citric acid also partly inhibited the response of the “M2” cell. No cell clearly responded to any of the bitter stimuli.