Pheromone‐mediated mating disruption of Choristoneura rosaceana: is the most attractive blend really the most effective?

Abstract

AbstractAn attractive four‐component pheromone blend containing a major component Z11‐tetradecenyl acetate, and three minor components, E11‐tetradecenyl acetate, Z11‐tetradecenyl alcohol, and Z11‐tetradecenyl aldehyde was tested as a mating disruptant against western Canadian populations of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae), in organic apple orchards in British Columbia. Efficacy of this four‐component blend was compared to that of partial pheromone blends containing the major component plus one or two minor components. A trapping experiment confirmed that, Conrel® fibre disruption dispensers containing the four‐component blend were more attractive than disruption dispensers containing the two‐ or three‐component partial blends. A small‐plot protocol was followed to compare atmospheric treatments with these blends as mating disruptants at a release rate of 10 mg ha−1 h−1 and from 1000 dispensers ha−1. Mechanisms of mating disruption, such as false‐trail following and camouflage of pheromone plumes, that may be evoked to a greater degree by an attractive blend, did not appear to augment the effectiveness of mechanisms invoked by the less attractive blends, as the proportion of mating among tethered females was equal in plots treated with these blends and was reduced by 85–90% compared to the nontreated control. When the four‐component pheromone blend was tested at different release rates, mating disruption in small plots began to break down at a release rate of 1.3 mg ha−1 h−1 using a dispenser density of 1000 ha−1. Above 1.3 mg ha−1 h−1 there was no dose response in release rates tested and at release rates below this dose the proportion of tethered females mating was the same as in the nontreated control. The four‐component pheromone blend was tested against, and found to be no more effective than, the two‐component partial blend at the threshold release rate of 1.3 mg ha−1 h−1 when it was released from 1000 or 250 disruption dispensers. Our results suggest that disruption mechanisms evoked by the attractive blend did not enhance the mating disruption effect provided by the simple blend, therefore a two‐component blend may be useful in an operational mating disruption program for C. rosaceana.