A rapid estimation procedure for within-tree populations of red oak borer (Coleoptera: Cerambycidae)

Abstract

Epidemic populations of red oak borer, Enaphalodes rufulus (Haldeman), a native wood-boring cerambycid beetle, appear to be a primary factor contributing to oak mortality across the Ozark Mountains of Arkansas, Oklahoma and Missouri. We developed a rapid estimation procedure (REP) to quickly, non-destructively and economically assess current density and infestation history of red oak borer in northern red oaks, Quercus rubra L., under outbreak conditions in the Ozark National Forest, Arkansas. The REP is a survey method for classifying individual trees that takes less than 2 min per tree and uses two variables: crown condition and number of emergence holes on the basal 2 m of a tree. Data obtained through intensive and extensive population sampling validate classification of trees into three REP infestation classes, which exhibited significantly different densities of measured red oak borer population variables. Numbers of emergence holes and previous generation galleries increased significantly across infestation classes from I (low) to III (high). Class I trees had significantly fewer attack holes than did Class II or III trees. Numbers of current generation galleries and live larvae were significantly lower in Class I than Class II trees, but Class III trees could not be distinguished from the other classes. The REP is an efficient sampling procedure as it facilitates greatly increased sample sizes, thus, allowing estimation of red oak borer populations at the stand, area and landscape level. Information provided by this kind of survey method may be vital to understand causes and extent of the current outbreak as well as predict future outbreaks and design silvicultural treatments for enhancing forest health.