FOREST ENTOMOLOGY Evaluation of Multiple Funnel Traps and Stand Characteristics for Estimating Western Pine Beetle-Caused Tree Mortality

The western pine beetle, Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae: Scolytinae), is a major cause of ponderosa pine, Pinus ponderosa Dougl. ex Laws., mortality in much of western North America. This study was designed to quantify relationships between western pine beetle trap catches [including those of its primary invertebrate predator Temnochila chlorodia (Mannerheim) (Coleoptera: Trogositidae)], and levels of tree mortality attributed to western pine beetle at 44 trapping sites (stands) and within Þve general locations (forests) in California. Furthermore, we evaluated relationships between forest stand characteristics and levels of western pine beetle-caused tree mortality. Preliminary analyses were conducted by PearsonÕs correlation coefÞcient (r) using tree mortality per hectare and percentage of tree mortality and 10 potential predictor variables.All predictorvariables thathad signiÞcantcorrelations(westernpinebeetleperday,western pinebeetle:T. chlorodia, percentageofwesternpinebeetle [percentageof total trapcatch represented by western pine beetle], trees per hectare, basal area of all tree species, basal area of P. ponderosa, meandiameter atbreastheight [dbh]and standdensity index)wereconsidered for linear andmultiple linear regressionmodels for predicting levels ofwestern pine beetle-caused treemortality. Our results suggest monitoring western pine beetle populations through the use of pheromone-baited multiple funnel traps is not an effectivemeans of predicting levels ofwestern pine beetle-caused treemortality. However, levels of western pine beetle-caused tree mortality can be efÞciently predicted (adjusted R 0.90) at large spatial scales (forests; 3,000Ð14,000 ha of contiguous host) by simply measuring stand density, speciÞcally the basal area of all tree species or stand density index. The implications of these results to forest management are discussed.