Chemotaxis to ethyl butyrate in wild-type and manipulated larvae. (a) Schematic of the multiple odor source assay. Source concentrations (M) used to generate ethyl butyrate gradients. (b) Average odor concentrations (mean ± SEM) obtained by FT-IR for sections along the length and the width (inset) of the arena shown in (a). Odor concentrations (mean ± SEM) were measured 4–12 minutes after loading. (c) Topographic reconstruction of the multiple odor source gradient shown in (b). The odorant line is indicated by the dashed box. The arena was subdivided into three concentration zones indicated by the gray lines (Z1 = low (0–8.7 μM), Z2 = medium (8.7–24.2 μM), and Z3 = high (24.2–60 μM)). (d) Odor-evoked behavior of Or42a-functional (left), Or42b-functional (middle) and wild-type (right) larvae tested in the multiple source assay. Source concentration range is indicated at the left. Gradient cartoons are not to scale and represent the relative concentration differences between the gradients. Low-concentration gradients are indicated with open gradient symbols and high concentration gradients with filled gradient symbols. Ten merged tracks, acquired consecutively, are shown per genotype and stimulus. Percentages of time in zones Z1–Z3 are represented at the right of the tracks as boxplots (n = 30), in which the boundaries represent first and third quartiles, the 'waist' indicates the median, whiskers are 1.5 interquartile distance, and outliers are marked with gray dots. Data that differ significantly from Or83b-/- (source range: 3.75–120 mM) are shaded (Wilcoxon test; corrected p < 0.0056). (e) Quantification of the overall alignment of trajectories with the gradient (n = 30 for all genotypes, except for Or35a-functional n = 20–30). Data that differ significantly from Or83b-/- (source range: 3.75–120 mM; gray boxplot at left) are shaded (Wilcoxon test; corrected p < 1.4 × 10-4).