Ponderosa pine characteristics associated with attack by the roundheaded pine beetle

The roundheaded pine beetle (Dendroctonus adjunctus Blandford [Coleoptera: Curculionidae, Scolytinae]) is an aggressive (tree-killing) bark beetle species that attacks several species of pine. Characteristics of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) trees chosen for attack by this beetle were studied in a current outbreak in northern Arizona. We found significant differences in basal area increment, crown width, lengths of internodes, subbranches, and needles, phloem thickness, and resin composition between attacked and unattacked trees. Attacked trees had significantly lower basal area increment and internode and needle lengths but longer subbranch lengths at the top of the crown and longer crown widths. Attacked trees also had thicker phloem and contained a significantly higher percentage of α-pinene in resin, but a lower percentage of longifolene than unattacked trees. A baited tree experiment showed that attacks by the roundheaded pine beetle did not affect resin composition through time. Overall, our results suggest that host selection by the roundheaded pine beetle may not be random and that tree growth characteristics and resin composition are probably important factors in host selection.