Beech Scale

Beech Scale,(Cryptococcus fagisuga,) is the main vector for beech bark disease. It is a small insect with piercing-sucking mouthparts and produces one generation per year. Eggs are laid around the beginning of July and hatch into crawlers four weeks later. These crawlers move around until they find a suitable place to pierce the tree.

The small crawlers can also be spread by wind. The Adult females are covered in a white waxy exudate that gives a heavily invested tree a woolly appearance. Treatment with insecticide is best done during the crawler stage.

Adults are cylindrical, dark reddish-brown to black, and 5 to 8 mm in length. The head is convex in front and has clubbed antennae. The pronotum, the hard cover on top of the insect’s midsection, widens posteriorly and does not conceal the head when viewed from above. The rear end of the wing covers is rounded, which helps to distinguish Dendroctonus from the Ips engraver beetles.

Circular to horizontal elliptic cankers form on the bark. Cracks form in the cankered bark. As large areas of bark are affected, the tree is girdled and killed. White wooly specks observed on the bark in August are wooly beech scales. The fungus that invades after scale feeding forms red, pimple-like fruiting structures in the cankers.

Life Cycle: Beech scale has one generation per year. Adults lay pale yellow eggs on the bark in midsummer, then die. Eggs are attached end-to-end in strings of 4 to 7 eggs. Eggs hatch from late summer until early winter. The immature scales that hatch from eggs are called crawlers or nymphs. Unlike adults, crawlers have functional antennae and legs and can move about. When a crawler finds a suitable location on a host tree, it forces its long, tube-like stylet into the bark and begins to suck sap from the tree.

Once a crawler begins to feed, it will molt to the second stage. Second stage crawlers have no legs and are immobile. They produce the white wax that eventually covers their bodies. Second stage crawlers overwinter and molt to the adult stage the following spring.

When eggs hatch, crawlers may remain under the body of the adult or move to other areas of the same tree. Some of the wingless crawlers are blown to other trees. A small number of crawlers may be carried for long distances in air streams above forest canopies. Birds probably transport crawlers short distances and perhaps long distances during migratory flights. In addition, the beech scale infestations in Newyork,connecticut. and New Jersey all centered on campgrounds or scenic areas, suggesting that humans likely play a role in moving scales long distances. For example, transporting infested beech firewood between mid-summer and early winter could allow mobile, first stage crawlers to infest new areas.

Damage: Beech scale infests tree bark, where it inserts its stylet (mouthpart) into the vascular tissue of the tree, and begins withdrawing fluids from the tissues. When several beech scales feed in relatively close proximity to each other, clusters of vascular cells in the tree collapse and cease functioning. This cell shrinkage causes fissures in the bark surface. The disease cycle begins when the fungal pathogens then infect these wounds, and, once established, hyphae of the fungus spread into and around the vascular tissues beneath the bark, eventually killing them. As these regions of infection expand and coalesce, enlarging the dead areas of bark, the tree is eventually girdled.

The combination of dead vascular tissues and decreased photosynthetic activity of the diminishing crown eventually causes tree death. Although feeding by beech scale weakens the tree, it is the subsequent infection by the fungal pathogens that ultimately kills the tree. The main sign of infestation of beech scale is the presence of small white specks (adult beech scale) covering the bark surface, while the main signs of infection by the fungal pathogens are patches of small red fruiting bodies of the fungi and/or open, oozing wounds on the bark surface.

The scales appear first their populations initially increase, then gradually decline as the bark dies, fungal fruiting bodies appear and cankers develop. Typical symptoms of infestation or infection include canker formation, canopy thinning, limb dieback breakage or tree death. Trees infected with beech bark disease usually succumb and die within five to 10 years after initial infestations of beech scale, depending on site quality and the level of other environmental stresses.

Controls: There is no practical chemical control of the beech scale in natural forests. The scale has several natural predators, but none has been sufficiently effective to stop the spread of beech bark disease. Resistance to beech scale insect attacks has been discovered in some beech trees and can be integrated into breeding programs to produce beech bark disease-resistant trees for restoration of the species.

Often infested trees may be saved if control measures are applied in time. If only a small number of pitch tubes are present, the bark below the pitch tube can be shaved away until the tunnel or entrance is located, then chipping away the bark will expose the gallery and the insects and they can be mechanically destroyed. Or the pitch tube can be struck soundly with a heavy rubber mallet or sledge. This crushes the pitch tube, closes the entrance tunnel, and squashes the beetles and grubs in the gallery beneath.

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