| Summary: | The white pine weevil, Pissodes strobi, is a major pest of regenerating
spruce in British Columbia, and the damage caused by weevil attack results in a
severe reduction in plantation productivity and wood quality. As a result, the
planting of Sitka spruce, except in a small portion of its range, is no longer
recommended in B.C. Control attempts have met with little success; however, it
is believed that host resistance will be an essential part of an effective Integrated
Pest Management plan for the weevil. My objective was to examine the induced
resin response and the constitutive resin canal system of Sitka spruce to identify
potential resistance mechanisms and to determine how those mechanisms were
affected by seasonal growth and development of the tree.
Histological examination of cross-sections of laterals taken at different
times during the season were used to compare the extent of components of the
constitutive resin canal system between resistant and susceptible families of
Sitka spruce. Similar methods were used to compare the capacity of resistant
and susceptible trees to produce a traumatic resin response. Weekly
measurements of leader apical bud phenology and radial growth were used to
determine if differences in leader growth and development existed between
resistant and susceptible trees which could affect resin canal density in the
leader. Artificial wounding of tree leaders at different times of the season and at
different densities of wounding was used to determine if there was a seasonal
effect on the production of traumatic resin and if the response level was related
to the wounding level.
Compared to susceptible trees, resistant trees tended to have larger inner
resin canals and thinner bark, and thus, a greater percentage of bark occupied
by inner resin canals. Furthermore, both resistant and susceptible trees showed
an increase in resin canal size and a decrease in resin canal density through the
season. The level of the traumatic response produced by artificially wounded
trees was significantly higher in resistant trees than in susceptible trees and was
also found to be highest in early flushing trees. No difference in rate of leader
radial growth was observed between resistant and susceptible trees, but buds
on resistant trees flushed earlier than those on susceptible trees. The traumatic
response was found to be lowest in trees wounded early in the season, and was
also found to increase in a density dependent manner with the wounding level.
Although several traits were present to a greater degree in resistant trees
than susceptible trees, no single trait was emphasized in every resistant
individual, suggesting that effective resistance is based on a combination of
traits. Furthermore, the variability of these traits through the season reinforces
the importance of host-insect phenology in the success or failure of an attack. === Forestry, Faculty of === Graduate
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