Bioactivity of sandalwood oil (Santalum austrocaledonicum) and its main components against the cotton aphid, Aphis gossypii

Control efficacy of sandalwood oil (Santalum austrocaledonicum Vieill) and its main components, alpha- and beta-santalol, which have not been tested before against Aphis gossypii Glover (Hemiptera:Aphididae), was investigated in the laboratory, greenhouse and field bioassays. The main constituents of the commercial sandalwood oil were found to be alpha-santalol (47.5 %), beta-santalol (18.7 %), bergamotol (7.2 %) and lanceol (9.1 %) according to GC and GC-MS analyses. The sandalwood oil was fractionated into an alpha-santalol-rich fraction (RF), beta-santalol RF, and a mixture of alpha- and beta-santalols by silica gel column chromatography. The purity of alpha-santalol RF was 75.4 % (ratio of alpha-:beta-santalol was 94:6) and that of beta-santalol RF was 34.6 % (ratio of alpha-:beta-santalol was 16:84). Laboratory bioassay showed that sandalwood oil, alpha- and beta-santalol RFs had the same and significantly higher repellency and control efficacy against A. gossypii than the two control treatments and that a mixture of alpha- and beta-santalols was toxic to the aphid. Santalol was comparable to imidacloprid (a neonicotinoid insecticide) in its efficacy against A. gossypii infesting Rose of Sharon, Hibiscus syriacus L., with 98.8 % mortality. The control efficacies of sandalwood oil (94.0 %), alpha-santalol RF (84.2 %), beta-santalol RF (90.6 %) and a mixture of alpha- and beta-santalols (88.7 %) against the A. gossypii infesting hot peppers were also comparable to each other in the greenhouse bioassay. Considering its control efficacy against A. gossypii, the application of sandalwood oil and its components may open the possibility of environmentally friendly management of A. gossypii.