Mating disruption is used to help manage the navel orangeworm on approximately 200,000 ha of tree nut crops. Aerosol dispensers are the most common formulation, and all formulations use an incomplete pheromone blend consisting solely of (Z11,Z13)-hexadecadienal. Profile analysis (examination of capture and males in pheromone traps as a function of spatial density of dispensers) demonstrated a sharp drop of males captured with a very low density of dispensers, and then an approximately linear relationship between 90 and approaching 100% suppression. This near-linear portion of the profile includes both dispenser densities in which crop protection has been demonstrated, and densities in which it is unlikely. Suppression of males in pheromone traps was lost the next night after dispensers were removed, suggesting that the active ingredient was not persistent in the orchard environment. During most of the summer preharvest period, turning the dispensers off 1 or 2 h before the end of the predawn period of sexual activity provides the same amount of suppression of sexual communication as emission throughout the period of sexual activity. This suggests that encountering the pheromone from the mating disruption dispensers had a persistent effect on males. During the autumn postharvest period, only emission prior to midnight suppressed communication on nights on which the temperature fell below 19°C by midnight. These findings and the analysis will help manufacturers refine their offerings for mating disruption for this important California pest, and buyers of mating disruption to assess cost-effectiveness of competing offerings.
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Vol. 113 • No. 3