Southern Pine Beetle - Identification
The adult southern pine beetle is 2 to 4 millimeters in length, has a rounded abdomen and is brownish-black in color. Males have a frontal groove on top of the head, while the females possess a broad elevated ridge called a mycangium on the anterior pronotum. Both males and females are capable fliers. Larvae are wrinkled, yellowish-white, legless grubs with prominent heads and stout, dark mandibles. Mature larvae are about 7 mm long.
Dependent upon temperatures, the beetles complete their life cycle -egg, larva, pupa, and adult- in 35 to 60 days, generally from April to September in the southern Appalachians. As many as seven generations (broods) may be produced annually, but in the northern extremities of its range (North Carolina, Virginia, and Maryland) as few as three generations may occur.
After mating, the female excavates the characteristic S- or serpentine-shape gallery and lays eggs along both lateral walls of the gallery. Eggs are deposited singly in discrete cavities (egg niches). SPB galleries normally contain one pair of adults. Eggs hatch in two to nine days and the larvae enter the cambium layer, then the inner bark, enlarging their galleries as they grow. When mature, larvae bore to the outer dead bark, create a cell and pupate. Generally, emerging adults leave the host tree and aggregate on an adjacent tree or leave the area to find a suitable new host tree. Trees from which the brood has emerged are covered with large numbers of small (~1/16 inch in diameter) emergence holes. Adult emergence may continue for an extended period of time.
SPB attacks normally occur on open trunks of trees from the base to the crown, usually attacking first at mid-trunk or in the lower crown. Large numbers of beetle adults and/or larvae girdle the tree by feeding under the bark on the phloem tissues. Besides their feeding, these bark beetles carry blue stain fungi on their bodies. Once introduced into a tree, these fungi colonize the sapwood and disrupt the flow of water to the tree crown, killing the tree. These fungi usually also cause “blue-staining” of the sapwood which can decrease the salvage value of the wood. It is believed that action of the blue-stain fungi make nutrients more readily available to the beetles and/or that the beetles feed on the fungi.
Bark beetle attacks can be recognized by the presence of boring dust, pitch tubes on the outside of the bark, characteristic galleries under the bark, and beetle adults and larvae in the inner bark.
The presence of "pitch tubes" on the bark of trees is one of the best ways to identify bark beetle attack. However, pitch tubes may not form on stressed trees. Instead, attacks are indicated by the presence of brown boring dust. On severely weakened trees, brown boring dust accumulated in bark crevices or on spider webs is often the only visible sign of early attack (Douce 1993).
Encyclopedia ID: p1382
