INTERACTION BETWEEN SITKA SPRUCE WEEVIL AND ITS HOST, PICEA-SITCHENSIS (BONG) CARR, A NEW MECHANISM FOR RESISTANCE

Available information on the interaction between Sitka spruce weevil, Pissodes strobi (Peck), and its host Sitka spruce, Picea sitchensis (B ong) Carr., is examined. Based on a theoretical consideration of this information, a new mechanism is proposed to explain the resistance exh ibited by some of the genetically distinct individuals of some provena nces of this species. Experimental evidence is presented to show that resistant trees can sufficiently affect P. strobi reproduction and pro geny development and survival to reduce this pest's ability to kill th e leaders of these trees when challenged with weevils containing alrea dy mature eggs. Our mechanism also provides an explanation as to how w eevils are able to avoid attacking and reproducing on resistant trees in which their progeny would fail.