Host Selection by Bark Beetles in the Mixed-Conifer Forests of California

Abstract

The capacity for bark beetles to discriminate between living host (Pinus ponderosa), dead host, and non-host trees(Abies concolor, Libocedrus decurrens), and between resistant and susceptible host trees prior to landing on the bole, was examined by measuring the landing rates of Dendroctonus brevicomis and D. ponderosae over month-long periods. Sticky traps were placed on the bole near the first living branches. Ponderosa pine exhibiting advanced symptoms of photochemical oxidant injury and root infection by Verticicladiella wagnerii were selected as the susceptible host trees. Some of these were screened over most of the bole to prevent initiation of boring activity and subsequent pheromone production and mass attack. Severe water stress was induced in another series of ponderosa pines by freezing, and injection of the herbicide, cacodylic acid. No significant differences in the landing rates of these bark beetle species were observed among the six classes of trees studied.