Behavioral sensitivity to ethyl butyrate in wild-type and manipulated larvae. (a) Schematic of the single odor source assay, with a 0.5 M ethyl butyrate source at position E7 on the lid of a 96-well plate used to generate a radial odor gradient. (b) Average odor concentrations in gaseous phase (μM) obtained by Fourier transform-infrared (FT-IR) spectroscopy along the length of the arena shown in (a). Odor concentrations (mean ± SEM) were measured 1–5 minutes after loading. (c) Topographic reconstruction of the single odor source gradient shown in (b). (d) Behavior of Or83b-/- larvae in the single odor source assay. Inset shows merged locomotor tracks for n = 5 animals, acquired consecutively, with the position of the ethyl butyrate source (60 mM) indicated by the black dot. Bar plots show the median relative occupancy with respect to the distance to odor source (n = 15 larvae). See Materials and methods for details on how occupancy distributions were calculated and evaluated with non-parametric tests for statistical significance. For clarity in data presentation, we have omitted the interquartile distances from this figure. (e) Odor-evoked behavior of wild-type and Or35a-, Or42a-, Or42b-, Or42a+Or42b-functional larvae in the single odor source assay for increasing source concentrations of ethyl butyrate (n = 15 larvae per genotype and stimulus) plotted as described in (d). Bins of relative occupancy that differ significantly from Or83b-/- are shaded (Wilcoxon test; corrected p < 0.0036). The first two bars of Or42a+Or42b-functional larvae tested at 240 μM are unshaded because large fluctuations around the mean make these data not significantly different from Or83b mutants.