Genetic variation in Eucalyptus regnans and Eucalyptus nitens for levels of observed defoliation caused by the Eucalyptus leaf beetle, Chrysophtharta bimaculata Olivier, in Tasmania

Chrysophtharta bimaculata, a leaf eating beetle, is the major insect defoliator of Eucalyptus regnans and Eucalyptus nitens plantations in Tasmania. Little is known about variability in host susceptibility. Levels of defoliation in E. regnans and E. nitens progeny trials were examined using a four point visual scoring technique. Large family differences were found in observed defoliation levels with heritabilities of around 0.3 for E. regnans and 0.4 for E. nitens. Differences between families in levels of defoliation were repeatable across seasons in E. regnans and the level of defoliation in both species was highly and favourably genetically correlated with growth prior to defoliation (rG around 0.8). Families which were initially growing faster suffered less observed defoliation, indicating that selection for rapid growth would indirectly lead to a reduction in defoliation levels. However, as level of defoliation was strongly genetically correlated with subsequent growth rate, later estimates of heritabilities for growth would be inflated by defoliation effects.