THIN BARK AND HIGH-DENSITY OF OUTER RESIN DUCTS - INTERRELATED RESISTANCE TRAITS IN SITKA SPRUCE AGAINST THE WHITE-PINE WEEVIL (COLEOPTERA,CURCULIONIDAE)

Bark thickness and density of outer resin ducts were examined in speci fic clones of Sitka splice, Picea sitchensis (Bong) Carr., to determin e their relationship with resistance status of those clones to the whi te pine weevil, Pissodes strobi (Peck). High density of outer resin du cts was associated positively with resistance. The most resistant clon es had a combination of thin bark and high density of outer resin cana ls, suggesting that interaction between these 2 traits is a strong res istance mechanism. Susceptible trees had both thin bark and low densit ies of outer resin canals. One highly resistant clone had thin bark an d few resin canals, suggesting the existence of other resistance mecha nisms.