The presence of taste and olfactory chemosensilla is demonstrated by using both morphological and electrophysiological techniques on antennae of Opius concolor, a parasitoid of tephritid larvae. Observation under the Scanning Electron Microscope revealed the presence of large sensilla trichodea with an apical pore, and of flat plates (sensilla placodea) extending almost the entire length of each antennomere. By means of currently used electrophysiological techniques, it was possible to record both the gustatory activity generated by sensilla trichodea following contact with KC1 100 mM and sucrose 100 mM solutions, and olfactory activity probably generated by sensilla placodea in response to volatile stimuli. The analysis of gustatory activity showed that each sensillum trichodeum consisted of at least three chemosensory units. This supports the assumption that in O. concolor single sensilla may, by providing different spike discharge patterns, which depend on the quality and intensity of the stimulus, provide the CNS with adequate information for peripheral discrimination among stimulating chemicals. Study of the sensory input of O. concolor with electrophysiological techniques may be of great scientific importance for possible applications in biocontrol of the olive fly.

An electrophysiological investigation was performed to analyse activity recorded in response to stimulation with concentrated and diluted solutions of NaCl, sucrose, formamidine acetate, and sodium acetate from labellar chemosensilla of the dipteran Protophormia terraenovae. A computerized analysis of this activity led to the finding of four kinds of spikes (A, B, C, and D) which differed in their wave forms. The forms of spikes A, B, and C are described in the literature as being evoked by activation of the specific salt, water, and sugar neurones respectively. The fourth type of spike (D) recorded in response to formamidine acetate and sodium acetate is probably generated by a fourth chemosensorial cell that has not yet been defined functionally. These two acetates evoke activities that are equivalent both in spike frequency and time distribution even at low concentrations. The results suggest that the acetate ion in the blowfly effectively stimulates the fourth chemosensory neuron present in the sensillum. The activation appears to be involved in signalling acidity to the insect.