Variation among Eucalyptus species in resistance to eucalyptus longhorned borer in Southern California

Abstract

Abstract Eucalyptus L'Héritier (Myrtaceae: Leptospermoideae) species are native to the Austro‐Malaysian region, but have been widely planted in temperate and subtropical regions around the world. In most regions where Eucalyptus have been imported, the Eucalyptus Longhorned Borer ( Phoracantha semipunctata F.) (Coleoptera: Cerambycidae) has been accidently introduced. Larvae of the beetle bore through the bark and mine along the cambium of stressed trees, usually killing their host. We report here the relative susceptibilities of 12 Eucalyptus species in two mixed‐species plantations in California, USA. These trees were stressed by water deficit resulting from a prolonged drought. Eucalyptus species that appeared resistant to the borer included E. camaldulensis Dehnhardt, E. cladocalyx F. Muller, E. sideroxylon A. Cunn. ex Woolls, and E. trabutii (an E. camaldulensis hybrid). Species that were more susceptible to attack were E. diversicolor F. Mueller, E. globulus LaBillardière, E. grandis Hill ex Maiden, E. nitens (Deane & Maiden), E. saligna Sm., and E. viminalis LaBillardière. Survival of trees was influenced by fine‐scale moisture variation resulting from slope and irrigation effects. Resistance characteristics of these Eucalyptus species did not correlate with taxonomic relatedness or bark characteristics, but did correspond to drought tolerance traits in their native habitat. Eucalyptus species that were resistant to attack by P. semipunctata were those that are most tolerant of drought in Australia.