Fig. 2. An illustration of P. americana males tracking female pheromone upwind (right to left) in a laboratory wind tunnel, containing the time-averaged plume boundaries of titanium tetrachloride smoke plume in 25 cm s^–1 wind. Each circle represents the body position at every 0.083 s. (A) Point source plume, 2.4 cm wide at the source spreads to 7.7 cm wide at the downwind end. (B) Ribbon plume, 1.5 cm wide at the source spreads to 6.1 cm wide at the downwind end. (C) Wide plume, 17 cm wide at the source spreads to 26.5 cm at the downwind end. (D) Cylinder plume, 7.6 cm wide at the source spreads to 68.1 cm at the downwind end.