Abstract
An outbreak of the native Eucalyptus longhorned borer (Phoracantha semipunctata, Coleoptera: Cerambycidae) coincided with a severe drought-induced dieback event in the Northern Jarrah Forest of southwestern Australia in 2010-2011. Although the behaviour of P. semipunctata is well known where it is exotic, little is known about its ecology in its native habitats within Australia. Intensive whole-tree sampling was used to investigate population levels, host preference, and within-tree infestation patterns in Eucalyptus marginata and Corymbia calophylla trees during the outbreak. The density of oviposition sites was similar between host tree species, whereas infestation levels were significantly greater in marri compared to jarrah, including 20% more larval galleries per oviposition site and 46% more emergence holes/m2. Larval damage in sapwood was extensive (mean of 48%) in both species. Significant positive correlations were found between density of oviposition sites, larval galleries, and emergence holes with stem diameter. This study is the first to establish the association between drought and outbreak levels of P. semipunctata in southwestern Australia, raising questions about the future impact of P. semipunctata with continued climate change in this region. It is also first to describe the within-tree distribution of the beetle in susceptible hosts in its native environment in Australia.