Biosynthesis of (2 E,4 E,6 E)-5-ethyl-3-methyl-2,4,6-nonatriene: the aggregation pheromone of Carpophilus freemani (Coleoptera: Nitidulidae)

The biosynthesis of the male-produced aggregation pheromone of Carpophilus freemani Dobson (Coleoptera: Nitidulidae) was studied by feeding the beetles on diet containing organic acids labeled with 2H (acetate, propionate, and butyrate) or 13C (acetate). The emitted pheromone, (2 E,4 E,6 E)-5-ethyl-3-methyl-2,4,6-nonatriene, was collected and analyzed by mass spectrometry and NMR spectrometry to determine the positions of isotopic labels. Studies with four deuterium-labeled synthetic pheromone standards demonstrated that mass spectrometry would be useful in locating the labels in beetle-derived samples. The pheromone is built up from one acetate unit, one propionate unit, and then two butyrate units, accompanied by the loss of the carboxyl carbon from one of the butyrates. The beetles will use propionic and butyric acid if it is available in the diet, but they are capable of making these acyl units from acetate if necessary. Biosynthetic steps for removing the acyl oxygens and making the double bonds of the pheromone are proposed to be as in usual fatty acid anabolism (reductions and dehydrations).