Forest Insect & Disease Leaflet 49

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Forest Insect& DiseaseLeaflet 49Revised April 2009U.S. Department of Agriculture Forest ServiceSouthern Pine BeetleStephen R. Clarke¹ and J. T. Nowak²The southern pine beetle, Dendroctonusfrontalis Zimmermann, is one of themost destructive insect pests of pines.Its range covers the southeastern UnitedStates from Pennsylvania and NewJersey to Texas, and from Arizona andNew Mexico through Mexico to Nicaragua (Fig. 1). Loblolly, shortleaf, pitch,pond, and Virginia pines are the favoredhosts in the southeast U.S., while Pinusoocarpa and P. caribaea are preferredhosts in Mexico and Central America.During outbreaks, the southern pinebeetle may infest all pine species, andeven marginal hosts such as spruce andhemlock may be killed.Populations often are concentrated ininfestations or “spots.” Periodicallybeetle numbers may rapidly increase tooutbreak levels, and healthy,vigorous pines may be attacked and killed as infestations expand. The southernpine beetle generally is inoutbreak status every yearsomewhere within its range.Average annual tree mortality in the U.S. often exceeds100 million board feet ofsawtimber and 30 millioncubic feet of pulpwood. From1999-2002, an outbreak inthe eastern U.S. caused inexcess of one billion dollars intimber losses. Over 225,000acres of pine forests in CentralFigure 1. Range map for southern pine beetle;Mexico distribution adapted from Salinas-MorenoAmerica were killed over thatet al. 2004.same period.Forest Entomologist, USDA Forest Service, Forest Health Protection, Southern Region,Lufkin, TX.2SPB Prevention Program Coordinator, USDA Forest Service, Forest Health Protection,Southern Region, Asheville, NC.1

Life Stages and AttackSequenceThe southern pine beetle has fourlife stages: egg, larva, pupa, andadult. The adult is dark red brownto black in color and 2-4 mm inlength (Fig. 2). The rear end isrounded and the head is visible fromabove. The egg is pearly white (Fig.3). The crescent-shaped larva iswhite with a reddish brown headFigure 2. Adult southern pine beetle.(Fig. 3). There are four larval stages, with the fourth stage averaging 3Attacking females bore through themm in length. The pupa is white (Fig.bark into the cambial layer. These at3) and develops into a callow adult,tacks usually occur in the bark crevices.which is soft and amber-colored prior toDuring initial attacks, the tree producesdarkening and hardening.resin and the beetles may be “pitchedout.” The male and female may worktogether to clear away the resin and successfully enter the bark. As a result,trees attacked by southern pine beetlesare characterized by pitch tubes in thebark crevices, which, dependent on treespecies, may be white or yellow andresemble popcorn or may be reddish(Figs. 4a, 4b).The female initiates the attack. Once asuitable host is located, the female releases aggregation pheromones, primarily frontalin. Frontalin, in combinationwith host odors, attracts a male for mating plus additional males and females.Arriving males also release pheromones, including endo-brevicomin,which may increase aggregation. If sufficient numbers of beetles are attracted,host resistance is overcome and the treeis successfully colonized. Verbenoneis a pheromone produced essentiallyby males, and at high concentrations itcan inhibit landing and cause beetles toswitch attacks to adjacent pines.Once beneath the bark, females beginconstructing S-shaped egg galleriesin the cambium (Fig. 5). Eggs are laidin niches cut in the wall of the gallery.The male follows behind the female,packing the galleries behind them tight-Figure 3. Left-right: Southern pine beetle egg, early instar larva, late instar larva, pupa, callowadult, mature adult.2

Figure 4 A (above) and B (left). Southern pinebeetle pitch with frass. The beetles occasionallybore ventilation or reemergence holesleading straight out from the gallery tothe bark surface. Newly-hatched larvaemine away from the gallery in the inner bark. Later-stage larvae move intothe outer bark to feed and pupate. Newadults chew small, round exit holes,creating a shotgun pattern on the barksurface after mass emergence (Fig.6). Both brood adults and reemergedparent adults can fly and attack newtrees. Beetles also inoculate pineswith blue stain fungi which penetratethe sapwood. The girdling of the hosttree from gallery construction and theblockage of the water conducting tissueby the blue stain fungi lead to rapid treedeath.Trees attacked by southern pine beetlestypically are divided into three categories: fresh attacks, faders, and vacated.Fresh attacks are characterized by theFigure 6. Southern pine beetle brood adult exitholes.Figure 5. Southern pine beetle egg galleriesand larvae.3

presence of reddish-white boring dust,tight bark with white phloem, and greencrowns. Adult southern pine beetlesmay be observed working in the pitchtubes, and clerid beetles, Thanasimusdubius, often are present (Fig. 7). Onceegg gallery construction is completeand the larvae hatch and begin feeding, the foliage begins to fade in color.A fading crown is symptomatic of asuccessfully colonized pine and usually indicates that southern pine beetlebrood is present. When a section ofbark is removed from fading trees, theS-shaped egg galleries characteristic ofthe southern pine beetle are clearly visible and the surface of the sapwood isbrown in color. Adult clerid beetles areno longer present on these brood trees.Trees vacated by the brood adults havenumerous exit holes in the bark andthe needles are either red or have fallenoff. The bark is very loose and peelsaway easily. White sawdust producedby wood-boring ambrosia beetles oftenis abundant at the base of vacated trees(Fig. 8).Figure 7. Adult of Thanasimus dubius, a cleridbeetle and predator of the southern pine beetle.or severely-stressed pines with compromised defense systems are often thetarget for these “pioneer” beetles. Oncea susceptible host is located, the attacksequence and pheromone release described above occur. As a tree becomesfully colonized, attacks switch to adjacent pines. When beetle populationswithin an area are high, an expandinginfestation can develop. However, onlyabout ¼ of trees attacked by dispersingbeetles in the spring develop into expanding spots of 20 or more trees.Generations overlap in the late springand summer, and eventually an expanding infestation will contain trees withall beetle life stages. Small infestations usually have one area with treesunder attack, called the spot head (Fig.9). As infestations enlarge, additionalspot heads may develop. The continualemergence of brood andparent adults, coupledwith pheromone production of attacking beetlesat the spot head(s), sustains infestation growth.Large infestations mayspread at a rate of 120ft/day, and satellite infestations may developnearby.Seasonal PatternsMost multiple-tree infestations areinitiated in the spring. Overwinteringbeetles emerge and disperse in searchof suitable host trees. Lightning-struckFigure 8. Boring dust of ambrosia beetles around the base of atree vacated by southern pine beetles.4During the warm summer months disper-

Figure 9. Infestation “spot” head with fading trees.sal is limited, and most beetles arelocated within expanding spots. Astemperatures cool in the fall, beetlesmay remain in spots or disperse to individual trees for the winter. Beetles mayoverwinter in all stages within a tree.Development slows during the winter,but there is no diapause. During warmwinter periods, development continuesand some emergence may occur. Winter-emerging adults may colonize unoccupied portions of the same trees fromwhich they emerged. A few infestationsmay remain active throughout the winter when temperatures are favorable.beetle larvae, pupae and callow adults, oftencompletely stripping the bark from the mainstems of infested trees during the winter.Persistent, freezing temperatures can lead tobrood mortality, particularly eggs and earlylarvae. Continuous high daily temperaturesin excess of 95o F also may kill broods.Population PatternsSouthern pine beetle populations within anarea can range from undetectable to outbreaklevels. An outbreak is defined as one ormore multiple-tree southern pine beetleinfestations per 1000 acres of susceptiblehost type. In the past 50 years in the GulfCoastal Plain, outbreaks have occurredon a 6-10 year cycle, though recentlypatterns have varied. The causes for theonset of outbreaks are unknown, thoughoutbreaks have been linked to extremelywet conditions in low-lying loblolly pinestands in the Western Gulf Coastal Plain.Population collapses have been attributedto lack of susceptible hosts, unfavorableenvironmental conditions, high numbersof natural enemies, and/or competition forhabitat beneath the bark.Natural ControlNatural enemies, including predators,parasitoids, and diseases, can maintainor reduce population levels. Thanasimusdubius is a major predator of both adultand larval southern pine beetles. However,there is no evidence that natural enemiescan stem the development of outbreaks.Ips bark beetles and borers may competefor reproductive space and food resourceswithin the bark. Woodpeckers may feed on5

Southern Pine BeetleManagementflagged, as is the current spot boundary. Theinfestation is classified as active or inactive,and the number of total and currentlyinfested trees recorded. Other data usuallycollected include spot head direction,number of spot heads, basal area, host type,mean host diameter, and number of freshlyattacked trees.An effective southern pine beetlemanagement program consists of thefollowing components:Monitoring and Prediction. Funnel trapsbaited with frontalin and host volatiles areset out each spring during the southern pinebeetle’s primary dispersal phase. The meandaily catch of southern pine beetle and theratio of southern pine beetle to T. dubius areused to predict current year southern pinebeetle activity.Suppression. Based on the datacollected during the ground evaluation,a suppression treatment is assigned to allactive infestations. Prompt suppression isthe key to reducing tree loss. Suppressiontreatments include cut-and-remove, cut-andleave, cut-and-hand spray, and pile-andburn. For cut-and-remove and cut-and-leavetreatments, all currently-infested trees arefelled toward the center of the infestation. Inaddition, a buffer of uninfested trees aroundthe expanding spot head also is felled (Fig.10). The downed trees are salvaged in thecut-and-remove treatment, and left on theground for cut-and-leave. Cut-and-removeis the most effective treatment, with anefficacy rate of 97% or higher. It also is themost recommended method, as landownersbenefit from the sale of harvested trees anddeveloping beetles are removed from thearea. When cut-and-remove can’t be appliedin a timely manner due to lack of access orno market for beetle-killed trees, cut-andleave is the preferred alternative. Cut-andleave is most effective when used on smallerinfestations ( 100 trees) in smaller diametertrees, and when applied between May andOctober. Cut-and-hand spray is rarely used,and insecticides labeled for this use may notbe currently available. Pile-and-burn maybe used on infestations in pine plantationswhen the infested trees can be pushed intopiles with a bulldozer and promptly burned.Suppression tactics using southern pinebeetle pheromones have been tested, butnone are currently operational. Small, slowgrowing spots may be monitored until theygo inactive (vacated by beetles) or grow to asize that warrants direct control.Detection. Most southern pine beetleinfestations are detected from aerial flights.Active infestations are indicated by groupsof 10 or more dying pines, including somewith fading crowns. Suspect infestationsmay be marked manually on maps, ora digital sketch-mapping system can beused. The sketch-mapping system utilizesa computer with a touch-sensitive screendisplaying a geo-referenced map selected bythe user. The system is tied into the plane’sGPS system and displays the current locationof the plane. Observers record suspectinfestations by touching the screen on thecorresponding point on the map display,and the coordinates for the infestation areautomatically recorded. Coordinates ofthe infestations can be downloaded intoa handheld GPS unit. The initiation andfrequency of detection flights is based onpredicted and observed southern pine beetleactivity. During outbreaks, flights every twoweeks may be needed from May throughSeptember.Evaluation. Detected infestations areground-checked to determine the bark beetlespecies responsible, current level of beetleactivity, and the need and practicality ofsuppression. Crews navigate to the spotsusing maps and/or the coordinates in aGPS unit. Access into the infestation is6

Figure 10. Diagram of cut-and-leave treatment illustrating buffer around currently-infested trees.Prevention. Direct tactics to suppresssouthern pine beetle populations have provensuccessful, as discussed above. However,forest managers and forest health specialistscommonly believe that the most effectivemethod of managing southern pine beetle isthrough preventing outbreak populations andcreating forest conditions that lessen impactsonce outbreaks occur. Stand density isthought to be one of the most critical factorsin determining the chances of spot initiationand the rate of spot expansion within astand. Thinning is the preferred forestmanagement tool used to attain desired standdensities, and it is widely recommended thatstands with a basal area greater than 120ft2 per acre should be thinned below 80 ft2per acre. Thinning reduces the likelihoodthat expanding infestations will becomeestablished by increasing tree vigor and bychanging the stand’s microenvironment.Increased tree vigor increases the likelihoodthat beetles will be “pitched-out” due tohigher resin flows. The changes in thestand’s microenvironment include increasedwind flow beneath the tree canopy andthe greater potential for disrupting thepheromone communication system of thesouthern pine beetle. In urban settings, itis recommended that the spacing betweenpines should be 20 feet.AcknowledgementsThis publication is a revision of the previousversion by R. C. Thatcher and P. J. Barry(1982). Their work provided valuableguidance in the preparation of this update.The authors also thank R. Hofstetter, T.Rogers, J. Meeker, and R. Billings for theirinput on the range map, and the latter two fortheir review of this leaflet.Illustrations: Fig.2- Erich G. Vallery, USDAForest Service - SRS-4552,;fig. 3- USDA Forest Service - Region 8Archive, USDA Forest Service,; fig.4a- Southern Forest Insect WorkConference Archive,; figs.4b, 5, 8 & 9- Ronald F. Billings, TexasForest Service,; fig.6- Lacy L.Hyche, Auburn University,;fig.7- John Moser, USDA Forest Service,; fig.10- E.Taylor, TexasCooperative Extension, and R. Billings,Texas Forest Service.7

ReferencesNebeker, T.E., J.D. Hodges, C.A. Blanche, C.R.Honea, and R.A. Tisdale. 1992. Variation in theconstitutive defensive system of loblolly pine inrelation to bark beetle attack. For. Sci. 38: 457-466.Belanger, R.P., and B.F. Malac. 1980. Silviculturecan reduce losses from the southern pine beetle.USDA Comb. For. Res. and Dev. Prog. Agric.Handbook. No. 576. 17 p.Nowak, J., C. Asaro, K. Klepzig, and R. Billings.2008. The southern pine beetle preventioninitiative: working for healthier forests. J. of For.106: 261-267.Belanger, R.P., R.L. Hedden, and P.L. Lorio, Jr.1993. Management strategies to reduce losses fromthe southern pine beetle. South. J. Appl. For. 17:150-154.Pye, J.M., T.S. Price, S.R. Clarke, and R.J. Huggett,Jr. 2005. A history of southern pine beetleoutbreaks in the southeastern United States through2004., R.F.,and C. Doggett. 1980. An aerialobserver’s guide to recognizing and reportingsouthern pine beetle spots. Agriculture HandbookNo. 560, Washington, D.C.: USDA Forest Service.19 p.Salinas-Moreno, Y., M.G. Mendoza, M.A. Barrios,R. Cisneros, J. Macías-Sámano, and G. Zúñiga.2004. Areography of the genus Dendroctonus(Coleoptera: Curculionidae: Scolytinae) in Mexico.J. of Biogeography 31: 1163–1177.Billings, R.F., and H.A. Pase III. 1979. A fieldguide for ground checking southern pine beetlespots. Agriculture Handbook No. 558, Washington,D.C.: USDA Forest Service. 19 p.Swain, K.M., and M.C. Remion. 1981. Directcontrol methods for the southern pine beetle.Agriculture Handbook No. 575, Washington, D.C.15 p.Billings, R.F., and J.D. Ward. 1984. How toconduct a southern pine beetle aerial detectionsurvey. Texas Forest Service Circular 267. Lufkin,TX. 19 p.Thatcher, R.C., and P.J. Barry. 1982. Southernpine beetle. Forest Insect and Disease Leafl. 49.Washington, D.C.: USDA Forest Service. 7 p.Clarke, S.R. 2001. Review of the operational IPMprogram for the southern pine beetle. IntegratedPest Management Reviews 6: 293-301.Thatcher, R.C., J.L. Searcy, J.E. Coster, and G.D.Hertel (eds.). 1980. The Southern pine beetle.USDA Forest Service Technical Bulletin 1631.267 p.Pesticides used improperly can be injurious to humans, animals, and plants. Followdirections and read all precautions on the labels. Consult your local forest pathologist,county agricultural agent, or State extension agent about restrictions and registered uses ofparticular pesticides.The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programsand activities on the basis of race, color, national origin, age, disability, and whereapplicable, sex, marital status, familial status, parental status, religion, sexual orientation,genetic information, political beliefs, reprisal, or because all or part of an individual’sincome is derived from any public assistance program. (Not all prohibited bases apply to allprograms.) Persons with disabilities who require alternative means for communication ofprogram information (Braille, large print, audiotape, etc.) should contact USDA’s TARGETCenter at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, writeUSDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington,D.C. 20250-9410, or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equalopportunity provider and employer.FS-R6-RO-FIDL#49/007-2010published by:USDA Forest ServicePacific Northwest Region (R6)Portland, Oregon8

Revised April 2009 U.S. Department of Agriculture Forest Service The southern pine beetle, Dendroctonus frontalis Zimmermann, is one of the most destructive insect pests of pines. Its range covers the southeastern United States from Pennsylvania and New Jersey to Texas, and from Arizona and New Mexico through Mexico to Nicara-gua (Fig. 1).