Progress in Study on the Fungi Associated with Dendroctonus valens Cellulase Produced by the Symbiotic Fungus Leptographium qinlingensis of Dendroctonus armandi Microstructure of blue-stain fungi (Leptographium terebrantis) associated with Dendroctonus armandi in the xylem tissue of Pinus armandi Bioassay of the Pathogenic Toxin of Leptographium yunnanense, A Fungus Associated with Tomicus piniperda Influence of Temperature on the Growth of Fungus ( Leptographium yunnanense) Associated with Tomicus piniperda Laccase Activity of Leptographium qinlingensis under Different Culture Conditions