Abstract: Polyunsaturated hydrocarbons (Type II pheromone components) have been reported to be synergists for unsaturated acetates, alcohols or aldehydes (Type I components) in several species of Lepidoptera. However, there is some debate over whether the active components are the hydrocarbons themselves or more volatile degradation products. We found females of the cone moth, Dioryctria mendacella (Lepidoptera: Pyralidae), produce (Z,E)-9,11-tetradecadienyl acetate (ZE9,11-14:Ac) and (Z,Z,Z,Z,Z)-3,6,9,12,15-pentacosapentaene (ZZZZZ3,6,9,12,15-25:H). The former elicits a strong EAG response from males while no response could be recorded to the latter. In field trapping tests, both compounds were individually unattractive to males, but blends of the two compounds were highly attractive. It was demonstrated that the relatively involatile hydrocarbon is actually released from the dispensers used and no significant degradation could be detected. Furthermore, analogues with fewer carbons and/or double bonds that might be expected to produce similar degradation products to the ZZZZZ3,6,9,12,15-25:H were inactive. This indicates a specific response to the hydrocarbon itself, further substantiated by the observation that related hydrocarbons did not interfere with the activity of ZZZZZ3,6,9,12,15-25:H. Thus a two-step conversion of cod liver oil was used to produce a blend of unsaturated hydrocarbons containing ZZZZZ3,6,9,12,15-25:H as the major single component, albeit only 30% of the total, and this was as attractive to male D. mendacella as an equivalent amount of the pure material in combination with ZE9,11-14:Ac.