Physiology of Pines Infested with Bark Beetles

Dendroctonus frontalis and I ps avulsus bore through the bark and tunnel in the phloem. The beetle inoculates the wood with fungi and the entrance holes and beetle galleries serve to expose the wood to the air. 2. The outer rings of the tree lose the capacity to conduct dye solutions successively from the first ring toward the center. This gradually advances to the center of the tree and cuts off the supply of water to the leaves which empty the top of water and die. 3. Failure of the outer rings to conduct dye solutions is intimately associated with drying of the wood. The suggestion is made that theaccumulation of air in the rings, which accompanies the loss of moisture, forms a resistance sufficient to stop the vertical and lateral transport of water. 4. The failure of the wood to conduct dye solutions is also closely associated with the penetration of the wood by fungi. Ceratostomellapini and fungus no. I are practically the only fungi which penetrate deeply into the wood during the early stages of attack. Inoculations show that C. pini growing alone is able to kill the trees, but fungus no. I has not been tested. 5. From the close connection between the drying and the position of the fungi in the wood, it is suggested that the drying is acceleratedby the action of the fungi on the cells. 6. The stoppage of conduction is probably also associated with the aspiration of the tori, as indicated by NELSON'S work. He suggests that blocking of the pits of the tracheids by the tori might account for the stoppage of conduction.