RELATIONSHIP BETWEEN CORTICAL RESIN ACIDS AND RESISTANCE OF SITKA SPRUCE TO THE WHITE-PINE WEEVIL

Cortical resin acids were analyzed both quantitatively and qualitative ly among 10 provenances and 11 genotypes of Sitka spruce, Picea sitche nsis Bong (Carr.), putatively resistant to the white pine weevil, Piss odes strobi (Peck), and compared with susceptible trees. Trees in 5 of the 11 resistant genotypes had significantly greater amounts of corti cal resin acid than susceptible trees. Of seven individual acids analy zed, pimaric, isopimaric, levopimaric, dehydroabietic, abietic, and ne oabietic acid, but not palustric acid, were found in significantly gre ater amounts in trees from resistant than susceptible provenances. Eig hteen percent of the variation in resin acid content could be accounte d for by variation in the capacity of cortical resin ducts, indicating that the other 82% of variation is a result of differences in resin a cid concentration in the resin. Trees with very high resin acid levels may have a greater capacity for resinosis than susceptible trees, may deter feeding, or may produce resin that is toxic to eggs and larvae. Canonical discriminant analysis revealed that several resistant clone s, particularly two from the Kitwanga provenance, could be distinguish ed from others on the basis of their resin acid profiles. Because it s eparated trees on the basis of genotype, but not according to degree o f resistance, canonical discriminant analysis may be more useful in '' chemotyping'' trees than in screening for resistance.