Unsaturated Cuticular Hydrocarbons Enhance Responses to Sex Pheromone in Spruce Budworm, Choristoneura fumiferana.

The primary sex pheromone components of the female spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), are (E)- and (Z)-11-tetradecenal, produced in 95:5 ratio. However, male flight responses to calling females in a wind tunnel were faster and maintained longer than responses to any synthetic aldehyde blend. Analyses of cuticular extracts from spruce budworm adults revealed series of n-alkanes and n-monoalkenes with predominantly odd numbers of carbon atoms from C23- C29 in both sexes. (Z,Z,Z)-3,6,9-tricosatriene and (Z,Z,Z)-3,6,9-pentacosatriene were identified only in cuticular extracts from females. Pheromonally naïve males showed wing fanning and circling responses to forewing scales from females but not to scales from males. Males also exhibited the same strong responses to scales excised from pharate females, indicating that the pheromone components are produced by females prior to emergence. (Z)-11-hexadecenal and (Z)-5-tricosene enhanced male responses to the primary sex pheromone aldehydes in wind tunnel bioassays, including higher proportions of in-flight and copulatory responses by males and increased time on the source. Addition of (Z,Z,Z)-3,6,9-tricosatriene to the 95/5 blend of (E)- and (Z)-11-tetradecenal released close-range copulatory responses including abdomen curling on treated septa. We propose that the sex pheromone blend of C. fumiferana is composed of the 95/5 blend of (E)- and (Z)-11-tetradecenal as primary components, with (Z)-11-hexadecenal, (Z)-5-tricosene and (Z,Z,Z)-3,6,9-tricosatriene fulfilling secondary roles in orientation and close-range courtship.