Scale insects, decay and canker fungi in American beech

Summary: Tripartite interactions among phytophagous insects, pathogens and their host plants provide insight into the role of host physiology in determining susceptibility to attack. American beech (Fagus grandifolia) often is simultaneously attacked by beech scale (Cryptococcus fagisuga), one or more Neonectria pathogens and Xylococculus betulae that can result in beech bark disease (BBD). Additionally, beech is frequently infected by heartrot-decay fungi. Cursory observations in 2011 suggested that beech scale and Neonectria lesion densities were lower and greater, respectively, on trees with decay. In 2012, digital image analysis was used to quantify densities of these organisms on 123 beech from the Adirondack region of New York. Three groups of study trees (n = 41) were used: Inonotus glomeratus-infected, Phellinus igniarius-infected and non-decay trees. Trees infected by decay pathogens supported lower densities of beech scale and higher densities of Neonectria. Densities of X. betulae did not significantly vary among decay groups. These results may be explained by decay-induced changes in host physiology. Additional work is needed to elucidate the potential role of host bark chemistry in the BBD complex.