Susceptibility of Eucalyptus globulus to Mnesampela privatadefoliation in relation to a specific foliar wax compound

Summary. Increased abundance of several aliphatic benzyland phenylethyl alkanoates were previously associated withreduced defoliation ofEucalyptus globulus Labill. by theautumn gum moth (Mnesampela privata Guenée) in twoclonally replicated F₂ families. We examine the robustnessof this association by comparing the abundance of theimplicated foliar wax compounds with defoliation levels inthree plantation sites and a genetics trial in northernTasmania. At all locations, the aliphatic alkanoate, benzyln-tetracosanoate (C₂₄), was found in significantly higherabundance in the foliar wax of E. globulus trees that had displayed low M. privata damage (designated resistant) compared to trees that had displayed high damage (designatedsusceptible). Further, when sites were combined, benzyln-tetracosanoate (C₂₄) accounted for 16 % of variation infield defoliation. Field defoliation was also positively correlatedto M. privata oviposition both in the field and onfoliage sprigs in a cage. In the cage bioassay, ovipositionaccounted for 20 % of variation in field defoliationmaking it a better predictor of tree defoliation in the fieldthan either field oviposition, which accounted for 9 % ofvariation, or screening foliage for the abundance of benzyln-tetracosanoate (C₂₄). Despite both benzyl n-tetracosanoate(C₂₄) and oviposition being related to field defoliation, therewas no statistically significant relationship between theabundance of benzyl n-tetracosanoate (C₂₄) and ovipositionin the field or cage bioassay. Further work is thereforerequired to determine if increased levels of this compound inthe foliar wax operates as a direct deterrent to M. privataoviposition.