Date of Award:

5-1986

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Ecology

Advisor/Chair:

Michael J. Jenkins

Abstract

The western spruce budworm, Choristoneura occidentalis Freeman (Lepidoptera: Tortricidae), is a serious defoliator of conifers in the western U.S. and western Canada. In 1985 epidemic levels of the budworm caused average tree defoliation in west-central Idaho to increase to 83%, up substantially from the 35% average tree defoliation of 1984. Associated with this increase in defoliation was a change in the relative stand defolation ranking between the two years. found to damage all types and In 1985 the budworm was developmental stages of reproductive structures of Douglas- fir, including: seedcone buds, pollen-cones buds, maturing cones, and seeds. Differential selection of feeding sites was observed, with a significantly higher proportion of larvae found in seedcone buds than in pollen-cone buds. Shortly after larval emergence, 25% of the total number of seed-cones buds were infested. A subsample of 171 branch tips indicated that only 9% of pollen-cones, while less than 2% of the vegetative buds contained larvae. A total of 640 cones from 21 trees were examined. Of these cones, 76% were infested with larvae, however not all of the seeds were destroyed. The average percent of destroyed seeds per tree was found to be exponentially related to the average current defoliation of the tree.

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