Electrophysiological recordings from l-type labellar chemosensilla were done by the tip-recording method, as previously described HODGSON 1955Hiroi 2002. Briefly, the proboscis was fixed at the base of the labellum. A glass capillary filled with Drosophila Ringer solution served as an indifferent electrode. 100 mM sucrose solution for stimulation contained 1 mM KCl as electrolyte. The recorded signals were digitized and analyzed using the custom software dbWave Marion-Poll 1996Marion-Poll 1995. Action potentials were detected by a visually-adjusted threshold set across the digitally filtered signal. The total number of spikes within 1 second was counted.