Impact of the Western Spruce Budworm (Lepidoptera: Tortricidae) on Buds, Developing Cones, and Seeds of Douglas-fir in West Central Idaho
Epidemic levels of the western spruce budworm (WSB), Choristoneura occidentalis Freeman, caused average tree defoliation in west central Idaho to increase from 35% in 1984 to 83% in 1985. Associated with this increase in defoliation was a change in relative stand ranking of defoliation between the 2 yr. WSBwas found to damage all types and developmental stages of reproductive structures of Douglas-fir. Differential selection of feeding sites was observed, with a significantly higher proportion of larvae found in seedcone buds than in pollen-cone buds. Of cones examined, 76% were infested with larvae, with the average percentage of destroyed seeds per tree exponentially related to the average current defoliation of the tree. However, even in heavily defoliated trees, some potentially viable seed remained.
Frank, C.J. and M.J. Jenkins (1987). Impact of the western spruce budworm (Lepidoptera: Tortricidae) on buds, developing cones, and seeds of Douglas-fir in West Central Idaho. Environmental Entomology, 16(1): 304-308.