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1 June 2002 Effects of Artificial and Western Spruce Budworm (Lepidoptera: Tortricidae) Defoliation on Growth and Biomass Allocation of Douglas-Fir Seedlings
Zhong Chen, Thomas E. Kolb, Karen M. Clancy
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Artificial defoliation has been used commonly to simulate defoliation by insect herbivores in experiments, in spite of the fact that obvious differences exist between clipping foliage and natural defoliation due to insect feeding. We used a greenhouse experiment to compare the effects of artificial and western spruce budworm (Choristoneura occidentalis Freeman) defoliation on the growth and biomass allocation of 3-yr old half-sib seedlings from mature Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco variety glauca] trees that showed phenotypic resistance versus susceptibility to budworm defoliation in the forest. Artificial clipping of buds mimicked the effects of budworm feeding on total seedling biomass when 50% of the terminal buds were damaged. However, artificial defoliation decreased seedling height, relative growth rate of height, and shoot: root ratio more than budworm defoliation, whereas budworm defoliation decreased stem diameter relative growth rate more than artificial defoliation. Half-sib seedling progeny from resistant maternal tree phenotypes had greater height, diameter, biomass, and shoot: root ratio than seedlings from susceptible phenotypes. We concluded that careful artificial defoliation could generally simulate effects of budworm defoliation on total biomass of Douglas-fir seedlings, but that the two defoliation types did not have equal effects on biomass allocation between shoot and root. Further, an inherently higher growth rate and a greater allocation of biomass to shoot versus root are associated with resistance of Douglas-fir trees to western spruce budworm defoliation.

Zhong Chen, Thomas E. Kolb, and Karen M. Clancy "Effects of Artificial and Western Spruce Budworm (Lepidoptera: Tortricidae) Defoliation on Growth and Biomass Allocation of Douglas-Fir Seedlings," Journal of Economic Entomology 95(3), 587-594, (1 June 2002).
Received: 6 July 2001; Accepted: 1 January 2002; Published: 1 June 2002

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biomass allocation
Choristoneura occidentalis
Pseudotsuga menziesii
Shoot:Root Ratio
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