Disruption ofEpiphyas postvittanamating behavior using synthetic pheromone was investigated in field cages and in replicated small-plot trials in a pinePinus radiata(D. Don) plantation. Polyethylene tubing dispensers releasing two formulations were tested: 70% (E)-11-tetradecenyl acetate and 30% (Z)-11-tetradecenyl acetate (monoene) or 92.6% (E)-11-tetradecenyl acetate, 2.8% (Z)-11-tetradecenyl acetate, and 4.6% (E,E)-(9,11)-tetradecadien-1yl acetate (monoene/diene). Field cage tests suggested that the second blend was the more effective disruptant, probably because of the presence of the diene. The concentration–response of males to the monoene/diene blend showed greater disruption of their normal response to caged females than the monoene alone (P500/ha of monoene in 100-m2plots (P<0.01). The percentage of tethered virgin females that were mated also was significantly reduced in all monoene treatments (P<0.01) compared with untreated controls. In larger plots (900 m2), the highest rate of monoene (1,000 dispensers/ha) resulted in 17% mating of tethered females (n= 64) compared with 93% mating in controls (n= 57). However, the second blend containing monoene/diene applied at 1,000 dispensers/ha reduced the percentage of mated females to 0 (n= 35), at an average pheromone release rate of 9.8 mg/ha per h. In a similar trial of the monoene/diene blend (900 m2plots), 73% of females mated in control plots (n= 80), compared with 1% (n= 90) in plot treated with 1,000 dispensers/ha (9.5 mg/ha per h).