In this study Sitka spruce characterized in three field sites as apparently resistant to attack by the white pine weevil. Pissodes strobi Peck, were evaluated for two criteria that could be used in a multi-component resistance index. There was no difference between resistant and susceptible trees in the mean numbers of feeding punctures produced by weevils caged on branches in the field, nor in feeding punctures or frass weight in a cut-twig, laboratory bioassay. However, five individual resistant trees were able to deter feeding by P. strobi significantly. Analyses of the monoterpene composition for trees from two sites disclosed significant differences in percent composition of several foliar compounds at two sites and several cortical compounds at one site. The most consistent difference, however, was a lower content of isoamyl isovalerate and isopentenyl isovalerate in resistant tree foliage at both sites, upholding the results of a 1987 study. Although other criteria must be included, the concept of applying a multi-component index to characterize resistant trees appears to be feasible.
FRDA Research Report 180 (1641 KB)
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Updated July 24, 2015