page_title: Beech bark disease
section_title: Beech scale insect
hierarchical_section_title: Beech bark disease / Mechanism of infection / Beech scale insect
caption_attribution_description: Beech scale nymph, about 0.3 mm long
context_page_description: Beech bark disease is a disease that causes mortality and defects in beech trees in the eastern United States, Canada and Europe. In North America, the disease occurs after extensive bark invasion by the beech scale insect, Cryptococcus fagisuga. Through a presently unknown mechanism, excessive feeding by this insect causes two different fungi to produce annual cankers on the bark of the tree. The continuous formation of lesions around the tree eventually girdles it, resulting in canopy death. In Europe, N. coccinea is the primary fungus causing the infection. Infection in European trees occurs in the same manner as it does in North American trees. Though the disease still appears in Europe, it is less serious today than it once was.
context_section_description: The beech scale insect, Cryptococcus fagisuga, is invasive to North America and is host-specific, feeding exclusively on beech trees.  It can be observed on the trunk and limbs of the tree as woolly, white tufts that will later develop into broad strips.  The woolly, white tufts and broad strips are the colonies of the beech scale insect that are formed in tiny crevices along the bark. An adult beech scale insect has a soft body, is yellow in color, ranges from 0.5 to 1.0 millimeter long, and has an elliptical shape.  The beech scale insect also has a stylet that it uses to penetrate the bark of the tree for feeding purposes.  There are no male beech scale insects and the female insects reproduce parthenogenetically.  In mid to late summer, the beech scale insect lays its eggs and dies.  The eggs are pale yellow and are laid on the bark in strings of four to eight eggs.  The first-stage nymphs  begin to hatch in late summer and eggs will continue until early winter.  They have short antennae and legs, and move around until they find a suitable and safe place to settle down and force their stylet into the bark to begin feeding.  At this point, they begin to secrete the woolly wax cover that they use for protection.  This is the second stage of their life cycle and when the spring season arrives they molt again and become adult females. A second type of scale insect, Xylococcus betulae, which is non-host-specific, is native to North America and causes beech bark disease to a lesser degree than Cryptococcus fagisuga.
caption: Beech scale nymph.
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