Multicomponent Index for Evaluating Resistance by Sitka Spruce to the White Pine Weevil (Coleoptera: Curculionidae)

Abstract

A prototype multicomponent resistance index was constructed for use in the selection of parent trees for a Sitka spruce, Picea sitchensis Bong (Carr.), breeding program and screening of progeny for resistance against the white pine weevil, Pissodes strobe (Peck). Data describing density of outer resin ducts, bark thickness, amount of volatile foliar terpenes, amount of cortical diterpene resin acids, feeding and oviposition deterrency, and repellency were collected from a clonal trial on Vancouver Island. These data were combined into a resistance index based on their hypothesized importance in weevil host selection. Clones differed in their complements of resistance traits, indicating that resistance is probably polygenic. There was a significant negative relationship between the resistance index and number of weevil attacks for the clones examined, suggesting that the resistance index could predict the resistance status of the trees. This relationship was improved if feeding deterrency and repellency were removed from the index. Our results suggest that a multicomponent resistance index is a promising tool for screening for resistance to P. strobi.