Optomotor anemotaxis polarizes self‐steered zigzagging in flying moths

ABSTRACT. Experiments with oriental fruit moth males, Grapholita molesta (Buck), provide evidence that a pheromone plume in zero wind elicits an endogenous, self‐steered programme of counterturning (zigzagging) flight, and that wind experienced in flight establishes the polarity of the counterturns; they become aligned so that displacement occurs toward the source, even after the wind is stopped. In zero wind, males located a pheromone source more frequently when they had experienced a wind after having already taken flight before the wind was stopped (46%) compared with those that took flight later and therefore only experienced wind while they were in contact with the ground (14%). Furthermore, males placed in a stationary pheromone plume in zero wind located the source, eventually, on 21% of occasions. The flight tracks of these males, as well as those having experienced a wind only while on the ground, often exhibited repetitive counterturns (zigzags) of c. 180–200d̀. However, the counterturns meandered around the flight tunnel, the inter‐reversal track angles having no consistent direction. Sometimes the males displaced down‐tunnel in the stationary plume, sometimes up, eventually locating the source and performing a courtship display. The inter‐reversal track angles of males counterturning in wind, on the other hand, displayed a consistent orientation of c. 60d̀ to either side of the wind line, resulting in consistent upwind displacement toward the source. With no pheromone present, with or without wind, counterturns were not observed.

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