(7E,11E)-3,5,9,11-Tetramethyltridecadienal: Sex Pheromone of the Strepsipteran Xenos peckii.

Xenos peckii is a strepsipteran parasitoid of the common North American paper wasp, Polistes fuscatus. Mate-seeking X. peckii males respond to a long-range sex pheromone emitted by the female, which remains permanently embedded within the abdomen of a mobile host wasp. During peak pheromone signalling, we excised the female from her host, severed the cephalothorax containing the pheromone gland, extracted it in hexane, and analyzed aliquots of combined extracts by coupled gas chromatographic-electroantennographic detection (GC-EAD). These analyses revealed a candidate pheromone component (CPC) that consistently elicited strong responses from male antennae. We identified the CPC as (7E,11E)-3,5,9,11-tetramethyltridecadienal based on its retention indices (RI) on three GC-columns, RI inter-column differentials, mass and NMR spectra, and synthesis of an authentic standard that matched the GC-retention and spectrometric characteristics of the CPC. For a field experiment, we prepared (7E,11E)-3,5,9R,11-tetramethyltridecadienal and (7E,11E)-3,5,9S,11-tetramethyltridecadienal. Xenos peckii males were caught in traps baited with either compound singly or a 1:1 mixture of the two but not in unbaited control traps. The sex pheromone of X. peckii resembles that reported for the strepsipterans Stylops mellittae and S. muelleri, (R,R,R)-3,5,9-trimethyldodecanal, suggesting a common biosynthetic pathway across taxonomic genera.