Forest Insect

& Disease

Leaflet 49

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 Nicaragua (Fig. 1). Loblolly, shortleaf, pitch, 

pond, and Virginia pines are the favored 

hosts in the southeast U.S., while Pinus 

1

Forest Entomologist, USDA Forest Service, Forest Health Protection, Southern Region, 

Lufkin, TX.

2

SPB Prevention Program Coordinator, USDA Forest Service, Forest Health Protection, 

Southern Region, Asheville, NC.

Southern Pine Beetle

Stephen R. Clarke1 and J. T. Nowak2

oocarpa and P. caribaea are preferred 

hosts in Mexico and Central America. 

During outbreaks, the southern pine 

beetle may infest all pine species, and 

even marginal hosts such as spruce and 

hemlock may be killed.

Populations often are concentrated in 

infestations or “spots.” Periodically 

beetle numbers may rapidly increase to 

outbreak levels, and healthy, 

vigorous pines may be attacked and killed as infestations expand. The southern 

pine beetle generally is in 

outbreak status every year 

somewhere within its range. 

Average annual tree mortality in the U.S. often exceeds 

100 million board feet of 

sawtimber and 30 million 

cubic feet of pulpwood. From 

1999-2002, an outbreak in 

the eastern U.S. caused in 

excess of one billion dollars in 

timber losses. Over 225,000 

acres of pine forests in Central 

America were killed over that 

same period.

Figure 1. Range map for southern pine beetle; 

Mexico distribution adapted from Salinas-Moreno 

et al. 2004. 
2

Life Stages and Attack 

Sequence

The southern pine beetle has four 

life stages: egg, larva, pupa, and 

adult. The adult is dark red brown 

to black in color and 2-4 mm in 

length (Fig. 2). The rear end is 

rounded and the head is visible from 

above. The egg is pearly white (Fig. 

3). The crescent-shaped larva is 

white with a reddish brown head 

(Fig. 3). There are four larval stages, with the fourth stage averaging 3 

mm in length. The pupa is white (Fig. 

3) and develops into a callow adult, 

which is soft and amber-colored prior to 

darkening and hardening. 

The female initiates the attack. Once a 

suitable host is located, the female releases aggregation pheromones, primarily frontalin. Frontalin, in combination 

with 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 tree 

is successfully colonized. Verbenone 

is a pheromone produced essentially 

by males, and at high concentrations it 

can inhibit landing and cause beetles to 

switch attacks to adjacent pines.

Attacking females bore through the 

bark into the cambial layer. These attacks usually occur in the bark crevices. 

During initial attacks, the tree produces 

resin and the beetles may be “pitched 

out.” The male and female may work 

together to clear away the resin and successfully enter the bark. As a result, 

trees attacked by southern pine beetles 

are characterized by pitch tubes in the 

bark crevices, which, dependent on tree 

species, may be white or yellow and 

resemble popcorn or may be reddish 

(Figs. 4a, 4b). 

Once beneath the bark, females begin 

constructing S-shaped egg galleries 

in the cambium (Fig. 5). Eggs are laid 

in niches cut in the wall of the gallery. 

The male follows behind the female, 

packing the galleries behind them tightFigure 2. Adult southern pine beetle. 

Figure 3. Left-right: Southern pine beetle egg, early instar larva, late instar larva, pupa, callow 

adult, mature adult.
3

ly with frass. The beetles occasionally 

bore ventilation or reemergence holes 

leading straight out from the gallery to 

the bark surface. Newly-hatched larvae 

mine away from the gallery in the inner bark. Later-stage larvae move into 

the outer bark to feed and pupate. New 

adults chew small, round exit holes, 

creating a shotgun pattern on the bark 

surface after mass emergence (Fig. 

6). Both brood adults and reemerged 

parent adults can fly and attack new 

trees. Beetles also inoculate pines 

with blue stain fungi which penetrate 

the sapwood. The girdling of the host 

Figure 4 A (above) and B (left). Southern pine 

beetle pitch tubes.

Figure 5. Southern pine beetle egg galleries 

and larvae.

Figure 6. Southern pine beetle brood adult exit 

holes.

tree from gallery construction and the 

blockage of the water conducting tissue 

by the blue stain fungi lead to rapid tree 

death. 

Trees attacked by southern pine beetles 

typically are divided into three categories: fresh attacks, faders, and vacated. 

Fresh attacks are characterized by the 
4

presence of reddish-white boring dust, 

tight bark with white phloem, and green 

crowns. Adult southern pine beetles 

may be observed working in the pitch 

tubes, and clerid beetles, Thanasimus 

dubius, often are present (Fig. 7). Once 

egg gallery construction is complete 

and the larvae hatch and begin feeding, the foliage begins to fade in color. 

A fading crown is symptomatic of a 

successfully colonized pine and usually indicates that southern pine beetle 

brood is present. When a section of 

bark is removed from fading trees, the 

S-shaped egg galleries characteristic of 

the southern pine beetle are clearly visible and the surface of the sapwood is 

brown in color. Adult clerid beetles are 

no longer present on these brood trees. 

Trees vacated by the brood adults have 

numerous exit holes in the bark and 

the needles are either red or have fallen 

off. The bark is very loose and peels 

away easily. White sawdust produced 

by wood-boring ambrosia beetles often 

is abundant at the base of vacated trees 

(Fig. 8).

Seasonal Patterns

Most multiple-tree infestations are 

initiated in the spring. Overwintering 

beetles emerge and disperse in search 

of suitable host trees. Lightning-struck 

or severely-stressed pines with compromised defense systems are often the 

target for these “pioneer” beetles. Once 

a susceptible host is located, the attack 

sequence and pheromone release described above occur. As a tree becomes 

fully colonized, attacks switch to adjacent pines. When beetle populations 

within an area are high, an expanding 

infestation can develop. However, only 

about 1⁄4 of trees attacked by dispersing 

beetles in the spring develop into expanding spots of 20 or more trees. 

Generations overlap in the late spring 

and summer, and eventually an expanding infestation will contain trees with 

all beetle life stages. Small infestations usually have one area with trees 

under attack, called the spot head (Fig. 

9). As infestations enlarge, additional 

spot heads may develop. The continual 

emergence of brood and 

parent adults, coupled 

with pheromone production of attacking beetles 

at the spot head(s), sustains infestation growth. 

Large infestations may 

spread at a rate of >120 

ft/day, and satellite infestations may develop 

nearby.

During the warm sumFigure 8. Boring dust of ambrosia beetles around the base of a mer months disper- tree vacated by southern pine beetles. 

Figure 7. Adult of Thanasimus dubius, a clerid 

beetle and predator of the southern pine beetle. 
5

sal is limited, and most beetles are 

located within expanding spots. As 

temperatures cool in the fall, beetles 

may remain in spots or disperse to individual trees for the winter. Beetles may 

overwinter in all stages within a tree. 

Development slows during the winter, 

but there is no diapause. During warm 

winter periods, development continues 

and some emergence may occur. Winter-emerging adults may colonize unoccupied portions of the same trees from 

which they emerged. A few infestations 

may remain active throughout the winter when temperatures are favorable.

Natural Control

Natural enemies, including predators, 

parasitoids, and diseases, can maintain 

or reduce population levels. Thanasimus 

dubius is a major predator of both adult 

and larval southern pine beetles. However, 

there is no evidence that natural enemies 

can stem the development of outbreaks. 

Ips bark beetles and borers may compete 

for reproductive space and food resources 

within the bark. Woodpeckers may feed on 

Figure 9. Infestation “spot” head with fading trees. 

beetle larvae, pupae and callow adults, often 

completely stripping the bark from the main 

stems of infested trees during the winter. 

Persistent, freezing temperatures can lead to 

brood mortality, particularly eggs and early 

larvae. Continuous high daily temperatures 

in excess of 95o

 F also may kill broods.

Population Patterns

Southern pine beetle populations within an 

area can range from undetectable to outbreak 

levels. An outbreak is defined as one or 

more multiple-tree southern pine beetle 

infestations per 1000 acres of susceptible 

host type. In the past 50 years in the Gulf 

Coastal Plain, outbreaks have occurred 

on a 6-10 year cycle, though recently 

patterns have varied. The causes for the 

onset of outbreaks are unknown, though 

outbreaks have been linked to extremely 

wet conditions in low-lying loblolly pine 

stands in the Western Gulf Coastal Plain. 

Population collapses have been attributed 

to lack of susceptible hosts, unfavorable 

environmental conditions, high numbers 

of natural enemies, and/or competition for 

habitat beneath the bark.
6

Southern Pine Beetle 

Management 

An effective southern pine beetle 

management program consists of the 

following components: 

Monitoring and Prediction. Funnel traps 

baited with frontalin and host volatiles are 

set out each spring during the southern pine 

beetle’s primary dispersal phase. The mean 

daily catch of southern pine beetle and the 

ratio of southern pine beetle to T. dubius are 

used to predict current year southern pine 

beetle activity. 

Detection. Most southern pine beetle 

infestations are detected from aerial flights. 

Active infestations are indicated by groups 

of 10 or more dying pines, including some 

with fading crowns. Suspect infestations 

may be marked manually on maps, or 

a digital sketch-mapping system can be 

used. The sketch-mapping system utilizes 

a computer with a touch-sensitive screen 

displaying a geo-referenced map selected by 

the user. The system is tied into the plane’s 

GPS system and displays the current location 

of the plane. Observers record suspect 

infestations by touching the screen on the 

corresponding point on the map display, 

and the coordinates for the infestation are 

automatically recorded. Coordinates of 

the infestations can be downloaded into 

a handheld GPS unit. The initiation and 

frequency of detection flights is based on 

predicted and observed southern pine beetle 

activity. During outbreaks, flights every two 

weeks may be needed from May through 

September.

Evaluation. Detected infestations are 

ground-checked to determine the bark beetle 

species responsible, current level of beetle 

activity, and the need and practicality of 

suppression. Crews navigate to the spots 

using maps and/or the coordinates in a 

GPS unit. Access into the infestation is 

flagged, as is the current spot boundary. The 

infestation is classified as active or inactive, 

and the number of total and currentlyinfested trees recorded. Other data usually 

collected include spot head direction, 

number of spot heads, basal area, host type, 

mean host diameter, and number of freshlyattacked trees.

Suppression. Based on the data 

collected during the ground evaluation, 

a suppression treatment is assigned to all 

active infestations. Prompt suppression is 

the key to reducing tree loss. Suppression 

treatments include cut-and-remove, cut-andleave, cut-and-hand spray, and pile-andburn. For cut-and-remove and cut-and-leave 

treatments, all currently-infested trees are 

felled toward the center of the infestation. In 

addition, a buffer of uninfested trees around 

the expanding spot head also is felled (Fig. 

10). The downed trees are salvaged in the 

cut-and-remove treatment, and left on the 

ground for cut-and-leave. Cut-and-remove 

is the most effective treatment, with an 

efficacy rate of 97% or higher. It also is the 

most recommended method, as landowners 

benefit from the sale of harvested trees and 

developing beetles are removed from the 

area. When cut-and-remove can’t be applied 

in a timely manner due to lack of access or 

no market for beetle-killed trees, cut-andleave is the preferred alternative. Cut-andleave is most effective when used on smaller 

infestations (< 100 trees) in smaller diameter 

trees, and when applied between May and 

October. Cut-and-hand spray is rarely used, 

and insecticides labeled for this use may not 

be currently available. Pile-and-burn may 

be used on infestations in pine plantations 

when the infested trees can be pushed into 

piles with a bulldozer and promptly burned. 

Suppression tactics using southern pine 

beetle pheromones have been tested, but 

none are currently operational. Small, slowgrowing spots may be monitored until they 

go inactive (vacated by beetles) or grow to a 

size that warrants direct control. 
7

Prevention. Direct tactics to suppress 

southern pine beetle populations have proven 

successful, as discussed above. However, 

forest managers and forest health specialists 

commonly believe that the most effective 

method of managing southern pine beetle is 

through preventing outbreak populations and 

creating forest conditions that lessen impacts 

once outbreaks occur. Stand density is 

thought to be one of the most critical factors 

in determining the chances of spot initiation 

and the rate of spot expansion within a 

stand. Thinning is the preferred forest 

management tool used to attain desired stand 

densities, and it is widely recommended that 

stands with a basal area greater than 120 

ft2

 per acre should be thinned below 80 ft2

per acre. Thinning reduces the likelihood 

that expanding infestations will become 

established by increasing tree vigor and by 

changing the stand’s microenvironment. 

Increased tree vigor increases the likelihood 

that beetles will be “pitched-out” due to 

higher resin flows. The changes in the 

stand’s microenvironment include increased 

wind flow beneath the tree canopy and 

the greater potential for disrupting the 

pheromone communication system of the 

southern pine beetle. In urban settings, it 

is recommended that the spacing between 

pines should be >20 feet. 

Acknowledgements

This publication is a revision of the previous 

version by R. C. Thatcher and P. J. Barry 

(1982). Their work provided valuable 

guidance in the preparation of this update. 

The authors also thank R. Hofstetter, T. 

Rogers, J. Meeker, and R. Billings for their 

input on the range map, and the latter two for 

their review of this leaflet. 

Illustrations: Fig.2- Erich G. Vallery, USDA 

Forest Service - SRS-4552, Bugwood.org; 

fig. 3- USDA Forest Service - Region 8 

Archive, USDA Forest Service, Bugwood.

org; fig.4a- Southern Forest Insect Work 

Conference Archive, Bugwood.org; figs. 

4b, 5, 8 & 9- Ronald F. Billings, Texas 

Forest Service, Bugwood.org; fig.6- Lacy L. 

Hyche, Auburn University, Bugwood.org; 

fig.7- John Moser, USDA Forest Service, 

Bugwood.org; fig.10- E.Taylor, Texas 

Cooperative Extension, and R. Billings, 

Texas Forest Service.

Figure 10. Diagram of cut-and-leave treatment illustrating buffer around currently-infested trees. 
8

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References

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Billings, R.F.,and C. Doggett. 1980. An aerial 

observer’s guide to recognizing and reporting 

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Billings, R.F., and H.A. Pase III. 1979. A field 

guide for ground checking southern pine beetle 

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Billings, R.F., and J.D. Ward. 1984. How to 

conduct a southern pine beetle aerial detection 

survey. Texas Forest Service Circular 267. Lufkin, 

TX. 19 p.

Clarke, S.R. 2001. Review of the operational IPM 

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	 Pacific Northwest Region (R6)

Portland, Oregon

FS-R6-RO-FIDL#49/007-2010

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directions and read all precautions on the labels. Consult your local forest pathologist, 

county agricultural agent, or State extension agent about restrictions and registered uses of 

particular pesticides.