The bark beetle attacks the tree carrying the "blue stain" fungal spoors into the sapwood. These spoors germinate and the fungus grows causing the sapwood to stain the blue or grey color. Once the tree is cut, sawn and the lumber dried, the fungus no longer grows and so the wood is not impared except for the color. There are widespread outbreaks of the Mountain Pine Beetle in the N.W. and parts of western Canada, so we will probably see more blue stained wood available. So Janette is right. There would be no stain without the beetle introducing the fungal spores.
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Bob
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