(A–E) In response to sucrose stimulation to the leg the proboscis is extended in a stereotypic motion pattern: (A) fly before stimulus, (B) sucrose stimulation, (C) rostrum lifting, (D) haustellum extension, (E) labella extension, (F) labella spreading. (G) Temporal quantification of proboscis extensions. The initiation time point of each step was determined in the video sequence and plotted with rostrum lifting set to zero. Data are shown for: single fly (magenta), multiple stimulations of three individual flies (A n = 13, B n = 10, C n = 13 stimulations), fed flies (red, n = 4 animals, 7 stimulations), mean ± SEM of the second stimulation of 12 individual flies (black). The following data points are not displayed on the graph: FlyA, stimulus (−28), labella spreading (+35); flyB, stimulus (−31, –54); flyC: labella spreading (32, 46). Statistical comparison of flies A–C (Mann-Whitney U test) revealed small significant differences for the following data points: A vs C, labella extension – labella spreading, p=0.0006; B vs C, stimulus – rostrum lifting, p=0.0304). No significant differences were detected when comparing fed flies to individual flies or to the 12 control flies. However, these flies failed to spread the labella in response to leg stimulation but not when stimulated at the labella. See also Video 1.