Abstract
White pine weevils, Pissodes strobi (Peck), caged on live clones (grafts) of resistant and susceptible Sitka spruce trees, Picea sitchensis (Bong) Carr., and petri dish experiments using cut branches from the same clones demonstrated that P. strobi feeding and oviposition was negatively correlated with the density of resin canals in the bark of the host tree. Weevils in cages containing resistant trees fed and oviposited preferentially in the internode below the leader, where resin canal density was lower (i. e., only the leader and not the entire tree was resistant). However, if given a choice, weevils departed from resistant trees and aggregated on susceptible trees. These experiments indicate that resistance is based on blockage by the tree of the normal preference of P. strobi for feeding and oviposition on the leader. This blockage is probably caused by repellency caused by the high resin concentration in the leader which, under natural conditions, forces the weevils to depart from resistant trees. The interaction of the weevil with other resistance mechanisms is discussed.
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