Host attractants for red weevil, Rhynchophorus ferrugineus: identification, electrophysiological activity, and laboratory bioassay.
A steam distillate from the freshly cut young bark of coconut palm Cocos nucifera was analysed by gas chromatography, combined gas chromatography-electroantennographic detection (GC-EAD) and GC-MS to detect host attractants for the curculionid weevil Rhynchophorus ferrugineus, one of the major coconut pests in Sri Lanka. A twin FID peak consisting of a minor and a major component was shown to possess electrophysiological (EAG) activity. The minor peak was identified as γ-nonanoic lactone 1, while the major peak was identified as 4-hydroxy-3-methoxystyrene 2. In an EAG assay the synthetic racemic nonanoic lactone 1 did not elicit a considerable response in the antenna of R. ferrugineus, whereas the laboratory synthesized 2 showed activity. In a laboratory bioassay using a Y-type olfactometer, synthetic 1 and 2 elicited moderate attractant properties to R. ferrugineus, whereas a 1 : 1 mixture of the compounds showed increased attraction over that of the individual compounds.