Based on prior, biological evidence for a male-produced aggregation pheromone in the crucifer flea beetle, Phyllotreta cruciferae (Coleoptera: Chrysomelidae), volatiles were collected and analyzed from males and females of this species feeding on host plant material. P. cruciferae is a pest of canola and other crucifer crops. For comparison, volatiles were similarly collected from the flea beetles, Aphthona flava, A. czwalinae, and A. cyparissiae, which are biocontrol agents of the serious weed pest, leafy spurge. Six male-specific compounds were isolated from P. cruciferae, and the same six compounds plus two additional ones were isolated from males of all three Aphthona species. The quantitative compositions of these blends were consistent within species but differed between species. Compound structures were studied by mass spectrometry, NMR spectroscopy, UV spectroscopy, polarimetry, chiral and achiral gas chromatography, molecular modeling, and microchemical tests. Three of the compounds were identified as the bicyclic sesquiterpenes, (+)-ar-himachalene, (+)-trans-a-himachalene, and (+)-g-cadinene. Two others were himachalene hydrocarbons which were known in general structure from certain fir tree species but with ambiguous stereochemistry. Finally, there were two himachalene alcohols and one norsesquiterpene ketone that is a himachalene analog. Except for (+)-ar-himachalene and (+)-g-cadinene, the compounds are either new natural products or new enantiomers of previously described natural products. Electrophysiological activity was demonstrated in A. flava for five of the compounds. The compounds likely have a pheromonal function.
Species 1: Coleoptera Chrysomelidae Aphthona flava
Species 2: Coleoptera Chrysomelidae Aphthona czwalinae
Species 3: Coleoptera Chrysomelidae Phyllotreta cruciferae (crucifer flea beetle)
Keywords: sesquiterpene, pheromone
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