Small scale field trials demonstrated that trans -11-tetradecenal containing a small amount of the cis isomer sex attractant of the eastern spruce budworm, Choristoneura fumiferana (Clemens), is capable of preventing males from locating virgin females. The corresponding acetate and alcohol had no detectable effect, although they reduced catches of males when present at low concentrations in traps containing the attractant. Aerial application of microencapsulated commercial trans -11-tetradecenal caused considerable disruption in the ability of males to locate virgin females.