Genetic variation in Eucalyptus globulus in relation to susceptibility from attack by the southern eucalypt leaf beetle, Chrysophtharta agricola

The southern eucalypt leaf beetle, Chrysophtharta agricola (Chapuis), is an outbreak insect pest of commercial Eucalyptus globulus Labill. plantations in south-eastern Australia. We surveyed a young E. globulus family trial in southern Tasmania to determine whether genetic variation existed in the susceptibility of trees to C. agricola field oviposition. The family trial consisted of 225 families, derived from open-pollinated seed collected from native stands at 24 different localities, representing nine geographic subraces. The survey showed that E. globulus subraces from Victoria were significantly more susceptible to C. agricola oviposition than Tasmanian subraces. Significant additive genetic variation within subraces was evident for the number of egg batches, larval clutches and their combination (infestation level), although these heritability scores were all low (egg batches hop 2 = 0.09; larval clutches hop 2 = 0.14 and infestation level hop 2 = 0.11). Subsequent tree defoliation was significantly positively correlated with infestation at a phenotypic, genetic and environmental level. No significant differences in C. agricola oviposition on foliage sprigs was detected among subraces in an ex situ caged oviposition experiment. However, the cage experiment proved to be a good predictor of field oviposition, accounting for 70 and 88% of variation in field oviposition among localities and subraces, respectively.