Foliar and cortical monoterpenes in Sitka spruce: potential indicators of resistance to the white pine weevil, Pissodesstrobi Peck (Coleoptera: Curculionidae)

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Abstract
To determine whether a resistant chemotype to the white pine weevil, Pissodesstrobi Peck, could be identified, the relative composition of monoterpenes in weevil-susceptible Sitka spruce, Piceasitchensis (Bong.) Carr., was compared to that in apparently resistant trees. Foliar and cortical analysis of trees from Green Timbers Nursery in Surrey, Nootka Island, Sayward, and the Nass River Valley, B.C., revealed significant differences between 38 resistant and 60 susceptible trees. The foliage of resistant trees, compared with that of susceptible trees, had significantly lower amounts of isoamyl isovalerate at three sites and lower amounts of isopentenyl isovalerate at one site. Amounts of a α-pinene, β-pinene, camphene, and camphor were significantly higher in some resistant trees, but these differences were not consistent between sites. Myrcene, β-phellandrene, and limonene levels were much higher in the cortex of susceptible trees than the resistant trees from the Nass River and Green Timbers Nursery. Thus none of the monoterpenes, singly or in combination, is a consistent indicator of resistance to the white pine weevil. The two isovalerates could possibly be used as indicators of resistance. However, a broader spectrum of resistance characteristics should be employed if breeding for resistance is desired.

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