Guidance system used in moth sex attraction

It has been proposed 1–4 that a flying male moth finds its way to a ‘calling’ female or other small, distant source of wind-borne sex pheromone using two contrasting anemotactic manoeuvres: (1) upwind flight in response to the onset or increase of the pheromone stimulus, maintained as long as the stimulus continues, and (2) cross-wind flight with switching between left and right of the wind line (the so-called ‘track reversals’ 4 or ‘tack reversals’ 5 seen in casting or zig-zagging) which occurs only in response to the loss or decrease of the pheromone stimulus. A simpler system can now be proposed in the light of wind-tunnel experiments on male summerfruit tortrix moths ( Adoxophyes orana ) entering homogeneous pheromone clouds. The moths did not fly persistently upwind with continuous pheromone stimulation, and their programmed left–right track reversals occurred in response to pheromone onset, not loss, and continued after pheromone loss but with widening cross-wind excursions between reversals.