the effect of five dosis of the synthetic sex pheromone of bonagota (=phtheochroa) cranaodes (meyrick) (a 9:1 blend of e,z 3,5 dodecanyl acetate and z9 hexadecenyl acetate) and the duration of the synthetic pheromone under field conditions were evaluated in a commercial apple orchard in vacaria, rs, brazil. no significant differences were observed among concentrations ranging from 0.25 to 3.0 mg per rubber septum. delta traps baited with two virgin females were ca. four times more attractive than those baited with the synthetic sex pheromone at the dosis of 3 mg per septum. rubber septa containing this amount of synthetic sex pheromone remained attractive for 120 days. comparing number of males captured in traps baited with the synthetic pheromone and males captured in traps with virgin females during seven months, a significant and positive correlation is observed, demonstrating that the seasonal variations in b. cranaodes population density are detected using the synthetic sex pheromone in delta traps.