Dispersal of the Eucalyptus Longhorned Borer (Coleoptera: Cerambycidae) in Urban Landscapes

We conducted 2 mark-recapture experiments in urban landscapes to examine the dispersal behavior of the eucalyptus longhorned borer, Phoracantha semipunctata (F.), a crepuscular beetle whose larvae bore into woody tissues of stressed or weakened eucalypts and fallen branches. Temporal changes in attractiveness of trees to beetles resulted in a correlation between beetle abundance and sample date. A mark-recapture study revealed that rates of beetle recapture declined with increasing air temperature, suggesting that beetles were less likely to disperse long distances on cool evenings. Dispersal behavior was not influenced by body size of either sex; however, larger males were more likely to gain mates than were smaller males. Estimated population size averaged ≈328 beetles per night. In another mark-recapture experiment, P. semipunctata were captured on 6 piles of eucalypt logs, 3 positioned inside a eucalypt grove and 3 outside. Males captured on the outside log piles were larger than those captured inside, suggesting that larger males were more likely to disperse longer distances than smaller males. Low 24-h recapture rates (<35%) of adult P. semipunctata in both experiments suggested that P. semipunctata dispersed actively in urban landscapes. These beetles may show little site fidelity because they must alternately search for vigorous eucalypts in flower on which they feed and for stressed larval hosts that are unpredictably distributed in time and space.