DOUGLAS-FIR NEEDLE ANATOMY IN RELATION TO WESTERN SPRUCE BUDWORM (LEPIDOPTERA, TORTRICIDAE) HERBIVORY

We compared 23 anatomical characteristics of current-year needles from five pairs of Douglas-fir, Pseudotsuga menziesii var. glauca (Beissner) Franco, trees that were either phenotypically resistant or susceptible to western spruce budworm, Choristoneura occidentalis Freeman, defoliation. The trees were mature (44-101 yr old) and were paired by size and microsite. Repeated-measures analysis of variance indicated needles from resistant trees were significantly longer, had thinner epidermal layers, and had proportionately more transfusion and less mesophyll tissue than needles from susceptible trees. There was no evidence that needle toughness or resin canal size was associated with resistance to budworm herbivory. It appears unlikely that anatomical features of the needles affect resistance to the budworm. The observed differences in needle anatomy may have resulted from stresses associated with repeated defoliation of the trees that were susceptible for reasons other than their anatomy.