VARIATION AMONG EUCALYPTUS SPECIES IN RESISTANCE TO EUCALYPTUS LONGHORNED BORER IN SOUTHERN CALIFORNIA

Eucalyptus L'Heritier (Myrtaceae: Leptospermoideae) species are native to the Austro-Malaysian region, but have been widely planted in tempe rate and subtropical regions around the world. In most regions where E ucalyptus have been imported, the Eucalyptus Longhorned Borer (Phoraca ntha semipunctata F.) (Coleoptera: Cerambycidae) has been accidently i ntroduced. Larvae of the beetle bore through the bark and mine along t he cambium of stressed trees, usually killing their host. We report he re 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 t hat appeared resistant to the borer included E. camaldulensis Dehnhard t, E. cladocalyx F. Muller, E. sideroxylon A. Cunn. ex Woolls, and E. trabutii (an E. camaldulensis hybrid). Species that were more suscepti ble to attack were E. diversicolor E Mueller, E. globulus LaBillardier e, E. grandis Hill ex Maiden, E. nitens (Deane and Maiden), E. saligna Sm., and E. viminalis LaBillardiere. Survival of trees was influenced by fine-scale moisture variation resulting from slope and irrigation effects. Resistance characteristics of these Eucalyptus species did no t correlate with taxonomic relatedness or bark characteristics, but di d correspond to drought tolerance traits in their native habitat. Euca lyptus species that were resistant to attack by P. semipunctata were t hose that are most tolerant of drought in Australia.