(A) GC-MS measurement of smoke. Many volatiles belonging to various chemical groups such as alcohols, ketones, and aldehydes are present in the smoke. (B) A snapshot of flies (blue), navigating straight smoke plume (gray) in laminar flow (blue arrow, lateral jets were turned off) with a representative trajectory of a navigating fly (red). (C) Probability distribution functions (pdf) of fly positions in the arena for wild-type CS flies navigating straight plumes (as in B) of smoke with increasing doses (top to bottom, n = 871, 1714, 1600, 1996, 4421 trajectories). Marginal pdfs in the x- or y-direction are plotted on a log scale on the exterior. (D) Integral of pdfs over the ribbon region (orange box, illustrated in the bottom plot of C) as a function of smoke dose. The dashed line represents chance probability. (E–F) Same as C-D but for ethyl acetate (EA, n = 369, 363, 907, 1351, 1604). (G–H) Same as C-D but for apple cider vinegar (ACV, n = 176, 212, 829, 1067, 1332). Dose values reported in C-H are the odor concentration of the straight plume released into the arena from the center straw (3 mm diameter). (I) PDFs in straight smoke plumes (dose 100%) for mutant flies, and at humidity saturation for wild-type CS flies. Mutant flies: Gr63a-/- (n = 1581); norpA (n = 4480); Orco-/- (n = 2420); anosmic (Gr63a-/-, Orco-/-, Ir8a-/-, Ir25a-/-; n = 3992). High humidity: (86.0 ± 3.9%; n = 2772). (J) Pdf integrated over the ribbon region (same region used in F-H) for control experiments.