Evaluation of Resistance to the Beech Scale Insect (Cryptococcus fagisuga) and Propagation of American Beech (Fagus grandifolia) by Grafting

Scions collected from diseased trees and from those without symptoms of beech bark disease (BBD) were cleft-grafted in 2003 and 2004 onto rootstock of unknown resistance to BBD. Grafting success varied among genotypes and year (30% in 2003 and 12% in 2004), and improved with increasing rootstock diameter. Successful grafts were used to test resistance to the beech scale insect, Cryptococcus fagisuga (the initiating agent of BBD) by introducing eggs onto the bark of scions and allowing time for the emergence of all developmental stages of the insects. Significantly fewer insects colonized scions collected from putatively resistant trees than those collected from diseased trees. In some cases, where egg placement overlapped a portion of the rootstock, insect colonies developed on the rootstock but not on the scion collected from resistant trees. Occasionally, scions from putatively resistant trees were colonized, whereas some of those from diseased trees were not. When scions from putatively resistant trees were heavily colonized, only adult insects were present and no eggs or other life stages of the insect were found. The findings indicate that the extent of resistance to the scale insect (hence to BBD) ranges from partial to total resistance.