Identification of volatile organic compounds from Eucalyptus detected by Gonipterus scutellatus (Gyllenhal) females

Abstract

This thesis concerns the development of semiochemical identification expertise and methodology at the University of Pretoria. The Eucalyptus snout beetle Gonipterus scutellatus was used as a model insect in developing these methods, firstly because it is a known pest in the Eucalyptus forestry industry of South Africa. Secondly, nothing is known about its chemical ecology and lastly, it is a relatively large insect that is easily worked on. Three main techniques were used namely: Electroantennography (EAG), Gas Chromatography Electroantennography Detection (GC-EAD) and Gas Chromatog- raphy Mass Spectrometry (GC-MS). EAG was used to difierentiate and identify certain Eucalyptus species that were expected to contain compounds that may function as either kairomones or allomones for G. scutellatus. The EAG process revealed that G. scutellatus responds more intensely to damaged Eucalyptus leaves as compared to undamaged leaves. The crushed foliage of the known hosts Eucalyptus globulus and E. viminalis gave larger responses than the crushed foliage from a known non-host E. citriodora. We sampled the volatiles from the crushed foliage of these three species and tentatively identified sixteen compounds from the E. globulus volatile profile that was antennally active for G. scutellatus females. The presence of these volatiles were subsequently investigated for E. viminalis and E. citriodora. The green leaf volatiles, (Z)-3 hexenyl acetate, (Z)-3-hexen-1-ol and (E)-2-hexenal and aromatic compounds, 2-phenylethanol, benzyl acetate and ethylphenylacetate often gave larger responses than the terpenes such as α-pinene, β-pinene and camphene. Crushed E. globulus leaves contained 2-phenyl ethanol, benzyl acetate, ethylphenylacetate, eucalyptol, α-pinene, (Z)-3 hexenyl acetate, (Z)-3-hexen-1-ol and (E)-2-hexenal that were antennally active. The E. viminalis profile had very little 2-phenylethanol and virtually no benzyl acetate. The E. citriodora volatile profile contained very little (Z)-3-hexen-1-ol, (E)-2-hexenal, 2-phenylethanol, benzyl acetate and ethylphenylacetate. These compounds may influence the host selection behaviour of G. scutellatusfemales. These volatiles can be tested in a behavioural bioassay in order to determine their effect on the Eucalyptus snout beetle G. scutellatus.