Variation and inheritance of resistance to defoliation by Christmas beetles, Anoplognathus sp (Leach) in eucalypts

Natural populations of eucalypts exhibit variation to defoliation by adult Christmas beetles at the species, subspecies and intra-tree levels. In this study we examine experimental populations of eucalypts in order to establish the origins of variability and the importance of genetic factors in host-insect interactions. A simple laboratory bio-assay was developed to overcome difficulties with measurement of defoliation in the field. Leaf area consumed (LAC) by beetles was used to estimate variation within and between several families of interspecific hybrid eucalypts. Extreme susceptibility to defoliation resulted from interspecific hybridisation where individuals from non-adapted parental species introduced susceptibility into a family. Host genotype, at the family and individual level were found to be significant in determining the amount of foliage consumed in bio-assays. Ranking of resistance classes in bio-assays was shown to correspond with field assessments of defoliation.