Attraction of Chryrsopa cognata (McLachlan) adults to two major aphid sex pheromone components, (-)-(1R,4aS,7S,7aR)-nepetalactol (NL) and (+) - (4aS,7S,7aR)-nepetalactone (NN) , was investigated in field experiments in Korea. C. cognata adults were much more highly attracted to NL than to NN. Even though NN also attracted significantly more C. cognata adults than did solvent control, there were no synergistic or additive effects on the trappings by NL. In a series of trapping experiments with blends of the two chemicals, C. cognata numbers trapped tended to increase with the content of NL, but never more than that by NL alone. As the amount of aphid sex pheromone components increased, more C. cognata were captured. However, the period of attraction for NL significantly decreased with time and after 50 days few C. cognata adults were attracted. C. cognata adults were mainly captured during the night and only a few were attracted in daytime during the late fall period. Even during the night, most of C. cognata were attracted from about 7:00 PM to 11:30 PM with apparently a longer period of activity in the summer than in the fall with an intermediate activity period in the spring. C. cognata adults caught in traps throughout the trap experiments were almost only males, in agreement with electroantenogram(EAG) results which showed that only male adults responded. The EAG response was stronger to NL than to NN. In addition to C. cognata, a few male adults of Chrysopa formosa (Brauer) and Chrysopa phyllochroma (Wesmael) were also captured in field pheromone traps.