Experiments during the flight of the overwintering generation of navel orangeworm revealed that Suterra NOW Biolure pheromone lures held in storage at -20 °C increased significantly in field effectiveness with time in storage over a period of 0 to 2 years. This increase in field effectiveness coincided with an increase in emission of (Z,Z,Z,Z,Z)-3,6,9,12,15-tricosapentaene as a proportion of (Z,Z)-11,13-hexadecadienal. These observations indicate that users should not presume equal effectiveness when lures are held over from the previous year, and suggest that manufacturers could improve lure effectiveness by increasing the proportion of (Z,Z,Z,Z,Z)-3,6,9,12,15-tricosapentaene in the lure emission.