Dendroctonus frontalis
From BugwoodWiki
Author: Scott M. Salom, Virginia Tech
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Contents |
Distribution and Hosts
The southern pine beetle (SPB) occurs in the southern and southeastern United States, extending as far west as Arizona and as far south as Central America. The northern range extends from southern New Jersey and Pennsylvania, west to southern Missouri, south to east Texas, and east into Florida. Generally, this insect occurs wherever Shortleaf and Loblolly Pines are grown. The beetle has been reported to attack and kill all pine species in its range. In the southeastern states, Loblolly and Shortleaf Pines are preferred, though Virginia, Pitch, Table-mountain, Longleaf, and Slash Pines are often also successfully attacked.
Description of Damage
Southern pine beetles are the most destructive forest insect pest in the southeastern U.S. They mass-attack the trunks of mature or overmature pine trees. The beetles bore through the bark and develop "s-shaped" galleries in the phloem tissue where the eggs are laid and brood develop. They also introduce a blue-stain fungus into the sapwood that eventually inhibits water flow in the tree. The colonization by the beetles and the fungus combined results in tree death only days after mass-attack. It may take weeks or even months (if attacks are in late fall) for the foliage to fade from green to red. Pitch tubes are often present at the entrance holes made by the beetles. In addition, reddish-yellowish boring dust may also be present in bark crevices or around the base of the tree. The tree attempts to pitch out the beetles and is sometimes successful. Beetle populations will remain at endemic levels for years until populations build up to epidemic levels for a two or three year period. These cycles occur about every 10 years. Often infestations that show up in the spring do not continue and will die out. However, when populations are high, infestations can expand almost like wildfire within pure pine stands, killing thousands of trees and covering hundreds of hectares. For trees that are killed, loggers try to salvage the wood as quickly as possible to minimize the amount of degrade. The blue-stain fungus is apparent in the sapwood, reducing the price at which sawtimber is sold.
Identification
Adults are 2 - 4 mm in length and brownish-black in color. They are cylindrical and somewhat stout to elongated in shape. The head is broad and prominent with a distinct longitudinal median groove bordered by a narrow elevation of tubercles (protrusions) on each side. The pronotum (shield behind the head) is slightly narrow at front, broadest at the middle, and about as long as wide. The wings are as wide as and over twice as long as the pronotum. Immature adults not ready to emerge from trees are light brown in color. Females lay eggs on alternate sides of "s-shaped" galleries in the phloem tissue. The eggs are opaque, pearly white, and shiny, measuring about 1.5 mm long by 1 mm wide. They are slightly oblong to oval in shape. The larva is a wrinkled, legless grub with three thoracic and 10 abdominal segments. They are yellowish white, and 2 mm long upon emergence from the egg, developing up to 5 - 7 mm long prior to pupation. The pupa is also yellowish-white. It has the form of the adult, but the wing pads and legs are folded beneath with the abdominal segments exposed. The pupae range in size from 3 - 4 mm in length. Larvae migrate from the phloem tissue into the bark as they develop. Pupae and callow adults occur near the outer bark in preparation for emergence.
Life History
The duration from egg to adult stages ranges from 26 to 54 days, depending upon the season. The beetles may have as few as three generations in Virginia and as many as seven generations in Texas. The beetles overwinter inside trees at all stages. In the spring when the dogwoods bloom, adults begin to fly. Females land on host trees, 2 - 9 m off the ground, bore through the bark, and if successful, produce a pheromone that attracts males and females together to attack the tree en mass. Females begin building egg galleries. Mating takes place in the gallery followed by female egg laying. Adults can re-emerge from galleries and attack new trees. Often within an infestation fresh attacked trees serve as a center of attraction. Usually as the infestation grows, adjacent trees succumb to attack, resulting in a group of trees producing pheromones. Therefore, infestations often move in one or more directions.
Control
Prevention is the best form of control. Forest stands should be thinned two to three times during the rotation. Thinned stands keep trees healthy and vigorous. Overmature stands are most susceptible to attack. Therefore, harvesting trees at rotation age should be followed. It is very important to aerial survey for SPB activity in the spring and periodically in the summer. This must be followed up by immediate ground checking. Quick action to protect a stand of trees is essential in trying to suppress the infestation. Active infestations can be halted using several cultural tactics. One is to salvage all old and new attacks, plus a buffer strip of unattacked trees in the direction the infestation was spreading. Size of buffer strips should range between 6 to 35 meters, depending on the number of fresh attacked trees present. Another option, for pre-commercial sized timber or hard to get to areas is to cut the timber down and leave it at the site. These trees should be felled toward the center of the infestation. The brood in the felled trees will not survive very well under the bark due to solar heating at the forest floor.
Knowledge of the complex chemical communication system used by this bark beetle species has stimulated scientists to develop a suppression tactic based on disrupting the flight of adult beetles. While the tactic is not yet operational, it will provide an important alternative in the near future.
Insecticides are available for application; however, they are only feasible for situations where the owner is interested in protecting individual trees. Please consult the Pest Management Guide for Horticultural and Forest Crops, Virginia Cooperative Extension Publication 456-017.
Further Reading
- Drooz, A.T. Insects of Eastern Forests. 1985. U.S.D.A. Forest Serv ice. Miscellaneous Publication No. 1426. 608 pp.
- Flamm, R.O., R.N. Coulson, and T.L. Payne. 1989. The southern pine beetle. pp. 531-553. In A.A. Berryman (ed.). Dynamics of Forest Insect Populations. Plenum Publ. Co.
- Thatcher, R.C. and P.J. Barry. 1982. Southern pine beetle. U.S.D.A. Forest Service Forest Insect & Disease Leaflet 49.
- Thatcher, R.C., J.L. Searcy, J.E. Coster, and G.D. Hertel. 1980. The southern pine beetle. U.S.D.A. Forest Service Technical Bulletin 1631.
External links
Salom, S.M. Southern Pine Beetle. ENTOMOLOGY PUBLICATION 444-243, August 1996.
Importance
The southern pine beetle is one of the most destructive pests of pines in the southern United States, Mexico, and Central America. This insect killed approximately 4.5 million board feet of pine timber from 1973 through 1977 in the southern United States. The beetle occurs from Pennsylvania to Texas and from New Mexico and Arizona to Honduras. It attacks and can kill all species of pines, but prefers loblolly, shortleaf, Virginia, pond, and pitch pines.
Identifying the Insect
The adult is shortlegged, about 1/8-inch (3 mm) long, and dark reddish brown to black in color. The front of its head is notched, and the hind end of its body is rounded. The larva is crescent-shaped and whitish, with an amber head. When fully developed, larvae are approximately the same length as adults. The pupae are also the same size and whire. The eggs are pearly-white and found in notches along either side of the adult egg galleries.
Identifying the Injury
The adults bore directly through the outer bark into the living bark. At each point of attack, the tree usually exudes resin which forms a small pitch tube about the size of a small piece of popped popcorn. Adult beetles construct winding, S-shaped galleries, which cut across one another and girdle the tree. Blue-stain fungi in the sapwood, introduced by the beetles, hasten the death of the tree. The first indication of tree mortality is discoloration of the foliage. Needles become yellowish, change to a red color, and-finally turn brown. Trees may be killed singly or in groups, ranging from a few trees to several hundred acres.
Biology
Adults construct winding galleries in the inner bark, where eggs are deposited in individual niches on each side of the galleries. The eggs hatch into small larvae within 4 to 9 days. The larvae mine for a short distance before boring into the outer bark where they pupate. One life cycle can be completed in about 30 days under ideal conditions. There are from three to seven generations per year, depending on latitude, elevation, and climate.
Control
Natural enemies, such as diseases, parasites, predators and weather, help maintain beetle populations at low levels and bring cyclic outbreaks under control. Integrated pest management may be achieved through any one or all of the following suppression techniques: rapid salvage and utilization of infested trees, piling and burning of infested materials, chemical control in high value resources, and cut-and-leave (May through October). To select the most appropriate strategy, the user is referred to the Integrated Pest Management Decision Key (IPM-DK). Good forest management is the most effective method of preventing losses from the southern pine beetle.
Gallery
  Photo by Ronald F. Billings, Texas Forest Service, Bugwood.org |  Photo by Texas Agricultural Extension Service Archive, Texas A&M University, Bugwood.org |
References
Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16. 98 pp. Taken from http://fhpr8.srs.fs.fed.us/forstpst.html
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