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

Summary. Increased abundance of several aliphatic benzyl and phenylethyl alkanoates were previously associated with reduced defoliation of Eucalyptus globulus Labill. by the autumn gum moth (Mnesampela privata Guenée) in two clonally replicated F₂ families. We examine the robustness of this association by comparing the abundance of the implicated foliar wax compounds with defoliation levels in three plantation sites and a genetics trial in northern Tasmania. At all locations, the aliphatic alkanoate, benzyl n-tetracosanoate (C₂₄), was found in significantly higher abundance 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 (designated susceptible). Further, when sites were combined, benzyl n-tetracosanoate (C₂₄) accounted for 16 % of variation in field defoliation. Field defoliation was also positively correlated to M. privata oviposition both in the field and on foliage sprigs in a cage. In the cage bioassay, oviposition accounted for 20 % of variation in field defoliation making it a better predictor of tree defoliation in the field than either field oviposition, which accounted for 9 % of variation, or screening foliage for the abundance of benzyl n-tetracosanoate (C₂₄). Despite both benzyl n-tetracosanoate (C₂₄) and oviposition being related to field defoliation, there was no statistically significant relationship between the abundance of benzyl n-tetracosanoate (C₂₄) and oviposition in the field or cage bioassay. Further work is therefore required to determine if increased levels of this compound in the foliar wax operates as a direct deterrent to M. privataoviposition.     

Identification of polyenic hydrocarbons from the northern winter moth, Operophtera fagata, and development of a species specific lure for pheromone traps

Summary. In order to elucidate the composition of the female sex pheromone of the northern (beech) winter moth, Operophtera fagata Scharf. (Lepidoptera: Geometridae), ovipositor extracts of unmated, calling females were analysed by gas chromatography with simultaneous electroantennographic and flame ionization detection (GC-EAD/FID). Male antennal responses indicated three active components, two of which had distinct matching peaks in the FID trace. Using coupled gas chromatography- mass spectrometry (GC-MS), these two compounds were identified as (9Z)-nonadecene (9Z-19:Hy), and (6Z,9Z)-nonadecadiene (6Z9Z-19:Hy), respectively. The third component, present in very small amounts only, was identified as (1,3Z,6Z,9Z)-nonadecatetraene (1,3Z6Z9Z-19:Hy), known as the sex pheromone of the common winter moth, O. brumata. Field tests revealed that traps baited with 6Z9Z-19:Hy and 1,3Z6Z9Z-19:Hy caugth large numbers of male O. fagata. Both compounds were found to be essential for attraction of O. fagata. In addition, the diene prevented captures of co-occurring O. brumata. In contrast, 9Z-19:Hy neither influenced the attractiveness of the two-component mixture towards O. fagata nor contributed to bait specificity. A binary mixture of 6Z9Z-19:Hy and 1,3Z6Z9Z-19:Hy in a ratio of 10:1, applied to pieces of rubber tubing, constituted a highly attractive and species-specific bait for O. fagata, which can be used for monitoring of the flight of this defoliator pest of deciduous forests.     

Constitutive or induced defences - how does <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> defend itself from larval feeding?

Summary. Following herbivory, induced responses involving plant secondary metabolites have been reported in a number of tree species. Although a wide range of plant secondary metabolites appear to operate as constitutive plant defences in trees belonging to the Eucalyptus genus, no induced responses have as yet been reported following foliar-chewing insect damage. We empirically tested whether branch defoliation (artificial and larval) of 2-year-old Eucalyptus globulus Labill. trees altered the abundance of specific plant secondary metabolites immediately (3 months after initial larval feeding) and 8 months after the cessation of larval feeding. Metabolites assayed, included essential oils, polyphenolic groups and foliar wax compounds and in all cases their abundance was not significantly altered by defoliation. However, the level of foliar tannins after 3 months of larval feeding did display a trend that suggested elevated levels as the result of defoliation, though this trend was not evident 8 months later, indicating that, if real, the response was a rapid and not a delayed induced response. The level of foliar tannins was also negatively correlated to both average larval survival and average percentage branch defoliation, suggesting that foliar tannins may operate as toxins and/or anti-feedants to M. privata larval feeding.