Distribution and abundance, stand and site conditions, host selection and oak defenses associated with a red oak borer (Coleoptera: Cerambycidae) outbreak in the Ozark National Forest, Arkansas

Passive trapping of flying adult red oak borer, Enaphalodes rufulus (Haldeman), during emergence of the 2001, 2003 and 2005 cohorts provided information on flight period, peak flight, sex ratios and revealed population densities varied both spatially and temporally. Number of northern red oak, Quercus rubra L., number of dead northern red oak, geographic area, topographic position, tree species diversity, northern red oak mean dbh and total number of trees were stand and site variables chosen as explanatory variables in models for red oak borer population density variables and for oak mortality. Low beetle catches and a marked decrease in emerging adult densities precluded firm conclusions in a host selection investigation among tree species and among northern red oaks in three red oak borer infestation history classes, low, moderate and high. Callus formation, but not phloem moisture, may be a physical defense mechanism in healthy trees and heavily infested oaks may not have the capacity to rapidly heal wounds and restore conductive tissues following invasion by stem-boring insects. Phloem tissue of low infestation history northern red oaks had the lowest total phenolics and protein-binding capacity and there were no compounds identified as present or in higher concentrations compared to moderately and highly infested trees. There were no differences in total phenolics or protein-binding capacity among three treatments inflicted to locally induce defenses, although a few compounds were found that may be defensive compounds. This research should facilitate future monitoring of red oak borer adults and elucidate factors contributing to this insect outbreak and oak mortality event.; Keywords. forest entomology, insect trapping, native pest, oak decline, tree defenses...