Semiochemical-based disruption of mate-finding behaviour in Choristoneura rosaceana (Harris) and Pandemis limitata (Robinson) (Lepidoptera: Tortricidae) in British Columbia apple orchards

Mate finding by male Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) was equally disrupted when the atmosphere was treated with an attractive pheromone blend, less attractive partial blends and an unattractive blend containing a behavioural antagonist. Similarly, for the sympatric tortricid species, Pandemis limitata (Robinson), mate finding was disrupted with an attractive pheromone blend, an off-ratio blend and Z11-tetradecenyl acetate which is an unattractive, shared main component of both species' pheromones. Mating disruption of both C. rosaceana and P. limitata was achieved simultaneously by a blend containing mostly the shared major component, or a 1:1 ratio of Z11- and Z9-tetradecenyl acetate, the minor component of the P. limitata pheromone. Pre-exposure of C. rosaceana males to their pheromone or to a partial pheromone blend did not after their response to calling virgin females in a wind tunnel. However, placement of sources of the complete blend or the partial blend upwind of the calling female significantly lowered the proportion of males contacting the female. The more attractive blend caused greater disorientation of males than the partial blend. Atmospheric permeation with Z9-tetradecenyl acetate induced male C. rosaceana to respond to normally unattractive synthetic pheromone sources containing this behavioural antagonist. The importance of Z9-tetradecenyl acetate as a synomone imparting distinct communication channels between C. rosaceana and P. limitata was demonstrated by induction of cross-species attraction in an atmosphere treated with this component. Female C. rosaceana delayed the commencement of calling in plots treated with pheromone and in one of two experiments reduced the total time spent calling. However, female C. rosaceana showed no alteration in mate preference for virgin or mated males in an atmosphere treated with pheromone. A physiological time scale based on thermal sums was used to model the timing of eclosion and oviposition by female C. rosaceana on apple in B.C., and hence when mating disruption formulations need to be applied. These results elucidate the mechanisms of mating disruption in C. rosaceana and P. limitata, and indicate that formulations containing Z11-tetradecenyl acetate alone or combined with Z9-tetradecenyl acetate are adequate to reduce mating of both species simultaneously.