Initiation and Termination of Oriental Fruit Moth Male Response to Pheromone Concentrations in the Field

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Abstract
The distance from the pheromone source at which Grapholitha molesta (Busck) males initiated walking, upwind flight, or wing fanning while walking varied directly with the pheromone emission rate. Roughly a 10-fold increase in emission rate resulted in a ca. 2-fold increase in mean maximum distance for initiation of these behaviors. Also, an apparent upper concentration threshold in males caused upwind flight to be terminated at increasing distances from the source with increasing emission rates. Thus, upper and lower thresholds apparently determine the boundaries of the “active distance” for upwind flight. There was much daily variation in mean maximum active distance, possibly due to temperature effects upon male threshold. The active distance estimates were used to design an optimal monitoring trap deployment strategy to minimize attraction of males from areas surrounding orchards. Using Bossert and Wilson's equation for active space, the average lower (initiation) threshold for upwind flight was 7.2 × 10 −17 g/cm 3 and the upper (termination) threshold was 2.1 × 10 −13 g/cm 3 . Their model should be altered so that active space is defined as the space where pheromone concentration is within both lower and upper thresholds for a particular behavior.