We investigated the attractiveness of synthetic volatile blends or individual volatiles of flowering rice panicles or flowering Scirpus juncoides spikelets to the sorghum plant bug Stenotus rubrovittatus (Matsumura). None of the individual chemicals tested attracted either sex of the bug. Synthetic volatile blends of flowering rice panicles composed of geranyl acetone, β-caryophyllene, n-decanal, methyl salicylate, β-elemene and n-tridecene attracted females. The synthetic blend of volatiles was just as attractive as natural flowering rice panicles to females. Other synthetic blends did not attract the bug. We sampled headspace volatiles from flowering S. juncoides spikelets with solid-phase microextraction and analysed them using gas chromatography-mass spectrometry. The main volatile emitted from S. juncoides was β-caryophyllene, one of the major volatile components of flowering rice panicles. β-Elemene was a common volatile found in flowering rice panicles and flowering S. juncoides spikelets. Therefore, we investigated the attractiveness of synthetic blends of flowering rice panicles and S. juncoides spikelets composed of β-caryophyllene and β-elemene. The synthetic blend of flowering S. juncoides spikelets significantly attracted males but not females. The synthetic blend of flowering rice panicles composed of β-caryophyllene and β-elemene did not attract either sex. These results suggest that β-caryophyllene and β-elemene are common active compounds responsible for attractiveness of flowering rice panicles and S. juncoides spikelets although some of the other volatile components act synergistically with these two compounds in natural plant odours.
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