The pine bark adelgid Pineus strobi (Htg.), known in the past as the pine bark aphid, is one of the most serious insect pests of nursery, ornamental and landscape Eastern White Pine in Tennessee. It occasionally attacks Scots and Austrian Pines. The pine bark adelgid, is covered with a white wax and feeds by sucking sap from the tree. Infestations are recognized by the presence of spots and patches of white cottony material on the bark of trunks and limbs, on buds or at the bases of needles. Trunks of heavily infested trees often appear to be whitewashed. This white material is often mistaken for a fungus. On older trees, the adelgid is more unsightly than injurious. Young trees, if heavily infested, become discolored, stunted or weakened and death may occur.
Distribution and Hosts
The pine bark adelgid is widely distributed in North America, occurring principally throughout the native range of Eastern White Pine. This insect is also found on Scots and Austrian pine.
Adult adelgids are small, purplish to yellow and covered with white strands of wax. Nymphs (immatures) resemble adults except for their smaller size. At first, nymphs are naked and yellow. They soon darken and begin to secrete white, waxy threads. The eggs are about 3 mm long and a milky to light yellow-brown color.
Pine bark adelgids overwinter in all stages, though usually as immature females. Development continues in late winter and eggs are laid in the spring. Winged and wingless forms hatch from these eggs. Winged individuals migrate to other trees and begin feeding. Wingless forms remain feeding on the tree and reproduce repeatedly. There are five or more generations per year.
Since permanent damage to trees is unlikely, little research has been carried out on control tactics. Application of insecticides is recommended for the trunks of transplanted large pine stock before the trunk is wrapped. Spray trees with dormant oil before growth starts in the spring. Treat with oil only when temperatures will remain above 6°C for 24 hours following treatment. Using a hand lens, look for white, cottony wax and the presence of active nymphs early in the growing season. Nymphs become active about mid-April. Continue to inspect trees throughout the growing season. Treat all pines in the surrounding area if any stage of this insect is seen. Use insecticides according to the state extension recommendations. The cottony wax will become dry and chalky if the adelgids have been killed.
- Drooz, A.T. 1985. Insects of Eastern Forests. U.S.D.A. Forest Service Miscellaneous Publication No. 1426. 608 pp.
- Johnson, W.T. and H.H. Lyon. 1991. Insects That Feed on Trees and Shrubs. Cornell Univ. Press, N.Y. 560 pp.