Odor delivery system faithfully reproduces the temporal stimuli. (A) A miniature photoionization detector was used to measure the temporal fidelity of a 2.5 Hz train of ethyl butyrate. Transients recover to baseline levels during, suggesting that the olfactometer faithfully produced temporally precise stimuli. (B) Flies were challenged to track a 10-9 dilution of ethyl butyrate (a stimulus that registered a distinct signal recorded by PID measurements as shown in (C). At this dilution, the plume deviation was not significantly different than the response to water vapor alone. However, the responses to flies tracking undiluted ethyl butyrate were significantly different than flies receiving either a 10-9 dilution of ethyl butyrate or water vapor. (t-test p < 0.01). n = 9 flies. (C) Distinct electrophysiological responses were observed to each pulse of ethyl butyrate which fully recovered to baseline when the solenoid valve controlling the water vapor was switched on. This refutes the possibility of any odor-induced contamination between ethyl butyrate pulses that might be below the PID detection limit. Shown are overlaid AFP traces recorded from 6 different preparations.