Two flight periods of Choristoneura rosaceana (Harris) were detected in a mixed forest near Quebec City using pheromone traps baited with the synthetic lure, Biolure, or newly emerged virgin females. During both flights, Biolure was considerably less attractive than C. rosaceana virgin females. Additional field tests using different compositions, ratios, and concentrations of C. rosaceana sex pheromone showed that blends containing three components (Z11-14: Ac, E11-14: Ac, Z11-14:0H) were more attractive than blends containing acetates only. Furthermore, the attractiveness of lures containing Z11-14: OH increased with concentration irrespective of the different ratios of Z11-14: Ac and the flight period, whereas no such effect was observed with lures containing acetates only. Moreover, during the summer flight males responded preferentially to the three component blends with a high rather than low ratio of Z11-14: Ac to Ell-14: Ac, although no differences were detected during the fall. This trend was observed irrespective of the concentration and the level of Z11-14: OH. The importance of using the appropriate pheromone blend to monitor each flight period of C. rosaceana will be discussed in relation to the seasonal biology of the parasitoid, Meteorus trachynotus Vier, an important natural enemy of the spruce budworm that requires C. rosaceana as an overwintering host.