Morpho-functional characterization of taste neurons in labellar apparatus in the medfly Ceratitis Capitata (Wied.)

MASALA, CARLA;LOY, FRANCESCO;SOLARI, PAOLO;SOLLAI, GIORGIA;MURONI, PATRIZIA;CRNJAR, ROBERTO MASSIMO

2013-01-01

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Abstract

The medfly (Ceratitis capitata Wied.) 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. Aim of the present work is to provide a morphofunctional map of the taste labellar apparatus, by investigating the relative distribution of different sensillum types and evaluating spike activity recorded from the labellar sensilla in response to NaCl, fructose, acids (citric and malic) and bitter compounds (quinine, quercetin and PROP). HRSEM and TEM observations indicate the presence of 6 pairs of Long type and about 40 pairs of Intermediate type labellar chemosensilla, each containing 4 different neurons. By analysis of spike waveforms in the responses, 4 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 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 M2 cell. No cell clearly responded to any of the bitter stimuli. None of them elicited any response from each of the four neurons in both Long and Intermediate type sensilla. In the light of our data, we assume that labellar sensilla do not respond to deterrent stimuli. This fact is not so unusual as previous studies in Drosophila revealed that Long type sensilla respond to salt and sweet but not to bitter stimuli, while Intermediate and Short type sensilla are activated by only a few bitter substances. The comprehension of the medfly taste responses may be critical for population control program.