Oviposition preference of a Eucalyptus herbivore and the importance of leaf age on interspecific host choice

1. Paropsine chrysomelids are eucalypt folivores for which it has been hypothesized that the availability of suitable age class foliage (i.e. young foliage) is a more important determinant of host use than the physical and/or chemical characteristics of foliage from different hosts. This prediction was tested by assessing the oviposition preference of Chrysophtharta bimaculata (Olivier) on excised branches of Eucalyptus regnans F. Mueller and E. nitens (Deane and Maiden) Maiden. 2. In cage trials, and as observed in the wild, beetles oviposited preferentially on E. regnans when the branches of both eucalypt species displayed the full range of foliar developmental classes, from immature to fully expanded. However, when the branches were pruned so that both species displayed only immature and expanding leaves, no difference in oviposition between the species occurred. Further, when the branches were pruned so that E. regnans displayed only fully expanded leaves and E. nitens displayed only immature and expanding leaves, females oviposited entirely on the latter species. 3. These results support and extend the hypothesis that C. bimaculata's ovipositional preference is dictated more by leaf age class than by the tree species from which the leaves derive. In the discussion it is proposed that a eucalypt that initiates and expands leaves rapidly will be less preferred for oviposition than one that develops and expands leaves slowly, because of the smaller area of its canopy with less sclerophyllous foliage.