“A Study of the Southern Pine Beetle”
The Southern Pine Beetle (SPB), Dendroctonus frontalis Zimmerman, is the number one killer of pine trees in the South. Across the South, from Virginia, south to Florida, and west to Texas, pine trees are numerous and in most of the southeastern United States they are the dominant tree species. Recent damage assessments estimate that from 1960 to 1990, SPB has caused in excess of $900 million of damage to pine forests. SPB makes its home in the inner bark layers of pine trees and ultimately kills its host tree. The biology of D. frontalis has been much studied because of their damaging effects on the paper and lumber industries and also because it is part of the reason why Red-cocked woodpecker populations are on the decline. The purpose of this paper is to explain the biology of SPB and elaborate on the impact that SPB has had and has on the southern environment. As more and more woodland is cleared for more and more people, it becomes increasingly important that we find ways to protect all the forests that we are able to. It is important that all the artificial stands of planted pine forests be spared from SPB infection, as artificial forests take pressure off of natural forest harvesting. By understanding the biology of SPB we can hope to prevent further insect-related tree damage.
The Southern Pine beetle makes it home in the cambium of pine trees. SPB most commonly attacks weakened species of Pinus taeda (loblolly), Pinus echinata (shortleaf), Pinus virginiana (Virginia pine), and Pinus rigida or (pitch pine). Pine beetles are exuded from species such as slash, longleaf, and eastern white pine because they have a high resin exudate that “pitches out” burrowing beetles better than other pines. Pine beetles are active all year, and are most abundant in the warmer months of spring summer and fall. SPB is a dark black or brown beetle, and is about 2-5mm long.The SPB is capable of rearing up to seven generations per year. The SPB begins it’s life cycle when a female “pioneer beetle” lights midway up a tree, (10-30 ft. up), and bores into the bark. The SPB appears to select mature trees through random landings. As a female bores her way into the bark, a semiochemical is released from her hindgut. As she makes her way into the tree the aggregation pheromone, frontalin, is released. The feces of SPB or “frass,” contain large amounts of frontalin. “Frontalin plays a dual role as both a sex pheromone and aggregation pheromone.” (McCarty et al. 1980) “For both sexes, the pheromone functions in close range communication to bring individual beetles together in sufficient numbers in order to overcome the host trees defenses” (Johnson and Coster 1978, Payne et al. 1978). When frontalin is mixed with the piney aroma of -pinene, it becomes irresistible to other SPBs. “In combination with frontalin, -Pinene appears to function as a kairomone arrestant; whereby, the pheromone draws beetles to the tree and the kairomone arrests their flight so they land” (Renwick and Vit 1970; Payne 1980a). As more and more males land, they release endo-brevicomin which is attractive to females, and verbenone which is unattractive to other males trying to mate. “When the number of SPB increases, the high concentration of the pheromones has an inhibitory effect and the tree looses its attractiveness” (Dajoz, 569). Also attracted to frontalin as a kairomone, is SPBs most important predator, Thanasimus dubius, A.K.A. the checkered beetle. Upon initial inhabitation of a tree by SPB, the checkered beetle begins hunting in the twisted serpentine galleries that SPB calls home. After colonization by SPB, the host tree is often overwhelmed by the sheer number of beetles boring into its bark. The earliest signs of possible SPB attack are tiny pellets of dried sap and boring dust accumulating around the base of the tree, in bark crevices, and on surrounding foliage. Another noticeable sign of SPB attack is the presence of white and globular lumps of dried tree sap (pitch tubes) oozing from the tree. Often the first indicator of SPB infestation is foliage discoloration. The mass attack of SPB is beneficial to the beetles because it severely weakens the defensive mechanisms of the host tree. The pine tree’s natural defense mechanism is its ability to “pitch out” invading pest by increasing its sap or oleoresin flow. After the tree becomes stressed and “pitches out” enough oleoresin to become dehydrated, the host tree is easily overcome by the pine beetle. Once mating has taken place, the females begin to bore through the bark, and construct long and sprawling S-shaped galleries. The female deposits up to 30 eggs in each niche that branch off from the gallery. The work of Dendroctus is distinguishable from other bark beetles because their galleries are always packed full with boring frass as the parent beetles finish working. The defining characteristic of SPB is its serpentine shaped gallery formation. Although other bark-beetles may be present in the same tree, they produce distinctly different I, Y, or H, shaped galleries.
While constructing galleries and laying eggs, SPB facilitates inhabitation of the host tree with a type of fungi commonly referred to as “blue stain” fungus. Stressed conifers provide favorable growing conditions for the fungus Ophiostoma minus. O. minus is an external symbiont of the SPB. The beetles inoculate their host trees with the blue stain and as a result the fungal infection inhibits oleoresin production in the tree. “Each female pine beetle has a “prothoracic mycangium” specialized for the cultivation and transportation of the fungi. Within each side of the mycangium the female SPB is able to maintain pure cultures of O. minus” (Happ, Happ, & Barras, 1971). The fungus itself is not fatal to the tree, but when combined with the girdling and bark etching of SPB it can be devastating. Another benefit the SPB acquires by introducing the blue stain fungus is food for their larva. Larvae feed on the fungal growth that lines the feeding chambers in the galleries. “It is likely that larval SPB obtain the majority of their nutrition from the mycangial fungi” (Payne, 1983b)
After mating, inoculation, and egg-laying, the female leaves and the eggs are left to hatch within their galleries. The egg is pearly white and hardly visible to the naked-eye. The egg hatches into a legless larva with a brown head in about one week. The larva feed on the blue-stain fungal growth and the cambium of the tree for about a month before entering the pupal stage. The pupil stage last for about two weeks before a soft brown, “callow” adult emerges. Callow adults remain in the bark until their exoskeleton has become sclerotized. A young adult bore towards the outer bark layer and exit by chewing an almost round “shot hole” through the bark. “Under favorable conditions, 600 plus beetles may emerge per square foot of bark and approximately four to seven generations of beetles can be produced per year” (Koch, 693) .
The SPB is not only detrimental to pine trees. Aside from logging, SPB is the leading killer of the red-cockaded woodpecker, (Picoides borealis). In 1996 the red-
cocked woodpecker (RCW) made the World Conservation Union’s (ICUN) “red-list” of endangered species. The red-cockaded woodpecker makes its home in the tops of old growth pine trees by carving out nesting cavities. Pine beetle infested forest, in areas where the woodpecker has made its home, has caused a significant decline in usable habitat for the RCW. It appears as if the woodpecker itself may initiate the attack of SPB. “RCWs irritate the area surrounding their cavity in order to make a resin barrier as a
means of protection against rat snakes, their number one predator” (Jackson et al. 1974). As the tree begins to ooze sap, pine beetles may be attracted to the -pinene, or they may be attracted to other pine tree distress signals triggered because of the freshly made woodpecker cavities. Red-cockaded woodpeckers prefer healthy trees and have been know to abandon SPB infested trees. Because RCW prefers healthy, old growth stands of pine forests, the introduction of pine beetles to the already endangered woodpecker’s habitat could decimate the remaining RCW population.
The Southern Pine Beetle is a menacing pest. In the south, from Texas to South Carolina, north pasts Tennessee and into Virginia, SPB has caused millions of dollars worth of damage. In spite of its economic spoils SPB has been studied intensively. Through years of research we are able to now understand the complexities of SPBs pheromone communication, its symbiont fungal harvesting, the dynamic predator prey
relationship between SPB and the Checkered Beetle, and its detrimental effects to the Red-cockaded woodpecker’s home in sappy pine cavities. The Southern Pine Beetle fills
an important niche in the ecosystem. However, as more and more timber is cut for lumber and cleared for housing, it becomes more and more important that we understand the biology of SPB. From an economic and environmental standpoint, it is increasingly important that we save as much standing plantation timber as possible, else wise, more pine trees (etc.) from natural forests will be cut to make up for the destruction caused by SPB.
Works Cited:
Dajoz, Roger. 2000. Insects and Forest Technique and Documentation. Paris
Intercept Lavoiser LTD. pg. 573
* Fig C. is from: (Thatcher et al. 1981). (chart published in book:)
McCarty, F.A., Billings, P., Richerson, J.V., Payne, T.L. and Edson, L.J. 1980. Response of the southern pine beetle to behavioral chemicals in the laboratory. J. Georgia Entomol. Soc. 15: 307-317 http://www.ento.vt.edu/~salom/Chemecology/chemecol.html (4 Oct 2004).
Happ, G. M., Happ, C. M. & Barras, S. J. (1971) Fine structure of the prothoracic mycangium, a chamber for the culture of symbiotic fungi, in the southern pine beetle, Dendroctonus frontalis. Tissue and Cell 3: 295308 http://www.dartmouth.edu/~mpayres/pubs/Klepzig.Flores-Otero.2004.pdf (4 Oct 2004).
Jackson, J.A. 1974. Gray rat snakes vs. Red cockaded Woodpeckers: Predator-Prey adaptations. Auk 91:
http://www.srs.fs.usda.gov/pubs/viewpub.jsp?index=714 (4 Oct 2004).
Johnson, P. and Coster, J.E. 1978. Probability of attack by southern pine beetle in relation to distance from an attractive host tree. For. Sci. 24: 574-580. http://www.southernregion.fs.fed.us/texas/healthy_for_ini/boswell_creek_spec_re ports/boswell_rtf/hfi_est_benefits_thinning_final.rtf. (4 Oct 2004).
Koch, Peter. Utilization of the Southern Pines. 1972. US. Dept. of Agriculture Forest Service. (Southern Forest Experiment Station) Washington D.C. pg. 689-695
Payne, T.L. 1979. Pheromone and host odor perception in bark beetles. pp. 27-57, in T. Narahashi (ed.). Neurotoxicology of Insecticides and Pheromones. Plenum Publ. Corp.
a. http://www.ento.vt.edu/~salom/Chemecology/chemecol.html (4 Oct 2004).
Payne, T.L. (1983) Behavior. In history, Status and Future Needs for Entomology Research in Southern Forest: Proceedings of the 10th Anniversary of the east Texas Forest Entomology Seminar. Texas Agriculture Experiment Station Texas A&M University System, College Station, Texas.
b. http://www.dartmouth.edu/~mpayres/pubs/Klepzig.Flores-Otero.2004.pdf (4 Oct 2004).
Renwick, J.A.A. 1970. Chemical aspects of bark beetle aggregation. Contrib. Boyce Thompson Instit. 24: 337-341. http://www.ento.vt.edu/~salom/Chemecology/chemecol.html (4 Oct 2004).
Thatcher, R.C.; Searcy, J.L; Coster, J.E.; Hertel, G.D. (Editors) (1981) The southern pine beetle. Technical Bulletin, Science and Education Administration, United States Department of Agriculture, Forest Service No. 1631 http://creatures.ifas.ufl.edu/trees/southern_pine_beetle.htm (4 Oct 2004).
http://www.fl-dof.com/Pubs/pests/spb/spb.html (4 Oct 2004).
* Fig C. is from: (Thatcher et al. 1981). (chart published in book:)
Dajoz, Roger. Insects and Forest Technique and Documentation, 2000. Intercept Lavoiser LTD -2000. Paris pg. 573
