Grosmannia clavigera is a species of sac fungus that causes blue stain in wood. It spreads to lodgepole pine, ponderosa pine, Douglas-fir, and whitebark pine trees from the body and a special structure in the heads of mountain pine beetles. The blue stain fungus has evolved a relationship with mountain pine beetles that allow them to travel from tree to tree on a special structure in the beetle’s heads and stops the tree from producing resin...