Spatial distribution of pheromone in vineyards treated for mating disruption of the grape vine mothLobesia botrana measured with electroantennograms

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Abstract
The spatial distribution of the pheromone of the grape vine moth.Lobesia botrana (Lepidoptera: Tortricidae), was measured in vineyards treated for mating disruption by using an electroantennogram technique (EAG). Five hundred dispensers per hectare, each containing 0.1 g of the main component of the sex pheromone (E,Z)-7,9-dodecadienyl acetate (E7,Z9-12: Ac) were evenly distributed in the experimental vineyards. The EAG amplitudes measured in the experimental plots were transformed into relative pheromone concentrations by means of a calibration curve. Mean relative pheromone concentrations in the center of a treated plot reached 2.31 × 10−4 relative units. No significant differences in the mean relative pheromone concentrations were found between replicate plots (P > 0.01). The mean relative pheromone concentrations measured within one plot along a transect at 5-m intervals also showed no significant differences between the sites. These results indicate that inside the borders of treated areas the pheromone was evenly distributed. No sites with significantly lower pheromone concentrations, frequently assumed to be the cause for higher trap catches in some areas, were found. However, the mean relative pheromone concentration rapidly declined more than 100-fold outside the border of the treated plot. At 10 m from the treated area, the EAGs showed no significant difference compared to the EAGs recorded in an untreated area. A rapid drop in the mean relative pheromone concentration was also found on a vertical transect through the canopy of the vineyard. Measurements in an untreated control block gave a mean antennal response approximately 1000-fold lower than in a nearby pheromone treated plot. The significance of the variation in the pheromone distribution for the success of the mating-disruption method is discussed.