Eggs: round to oval in shape, pearly white in colour, and are found in galleries located in the inner bark of pine trees.
Larvae: crescent shaped, white wrinkled bodies with a caramel coloured head. Upon hatching, the larvae are about 2 mm long. Mature larvae are about 7 mm long.
Pupae: same colour and size as the larvae.
Adult: immature adults or “callow”, are yellowish-white in colour, but they soon turn dark brown as their cuticle hardens. The size of adults ranges between 2 and 4 mm.
Egg Larva Pupa
Callow adult Adult
Images retrieved from: http://www.barkbeetles.org/spb/spbbook/Chapt2.html
Female southern pine beetles select a host tree on which they drill into the inner phloem using their mouthparts, creating galleries where they are able to mate and lay their eggs. The eggs hatch 3 to 9 days after oviposition. The emerging, legless, new larvae feed on the inner bark and bore galleries perpendicular to the adult egg galleries, moving toward the outer bark where they pupate. The pupal stage lasts from 5 to 17 days. The callow (immature) adults stay right under the bark for 6 to 14 days until the cuticle hardens and becomes dark in colour. The adult beetles then bore their way outside of the bark, and fly to attack a new host tree.
Photo: USDA Forest Service - Region 8 - Southern , USDA Forest Service, Bugwood.org
Southern pine beetle egg galleries
All species of pine are potential hosts for SPB where it is established (Thatcher et al., 1980). However, SPB has been documented to have different preferred host pine tree species depending on where it is found.
In southern United States, SPB preferred hosts are:
loblolly pine (Pinus taeda L.)
shortleaf pine (Pinus echinata Mill.)
pond pine (Pinus serotina Michx.)
Virginia pine (Pinus virginiana Mill.)
pitch pine (Pinus rigida Mill.)
SPB can also attack the following species, which are found in Canada:
eastern white pine (Pinus strobus L.)
Norway spruce (Picea abies L.)
Austrian pine (Pinus nigra Arnold)
Scots pine (Pinus sylvestris L.)
red pine (Pinus resinosa Ait.)
Photo: David Stephens, Bugwood.org
It is important to note that environmental stress factors such as drought, lightning strikes, and fire can increase the susceptibility of host trees to SPB infestations.
Photo: Erich G. Vallery, USDA Forest Service -
Signs of SPB infestation often first appear at the top of the tree and then move down.
There are three main stages for SPB attacks with distinctive signs - green crown, yellowish crown, and brown crown.
Stage 1: Green Crown
adult SPBs start boring into the living bark of their host
tree exudes fresh resin in response to the attack to pitch out the beetles
crown is still be green
resin later hardens on the outer bark forming what looks like a “popped popcorn”
Photo: USDA Forest Service - Region 8 - Southern ,USDA Forest Service, Bugwood.org
Hardened resin from a host tree infested with SPB
Stage 2: Yellowing Crown
more beetles gather on the host tree
tree becomes weak and is no longer able to defend itself
foliage turns a yellow colour
Stage 3: Brown Crown
Photo: Gerald J. Lenhard, Louisiana State University, Bugwood.org
Image showing signs of a SPB infestation at three different stages: Green, yellow and brownish crown
Blue-stain fungi (Ophiostoma minus) can be introduced to the sapwood of pine trees by the SPB, or other species of beetles or mites. The fungi cause the trees to become weaker and therefore, to die more quickly. The blue staining fungus is an ectosymbiont of the SPB, which means that it is often carried by the adult SPB as they attack new trees.
The blue staining fungus disrupts the interaction between the larvae and the nutritional fungi that are found in the wood fibre thereby, causing the larvae to die (Hofstetter et al., 2005). However, as the fungi weakens tree defenses, it may be an important determinant in tree susceptibility to SPB (Otrosina et al., 1997)
Photo: Ronald F. Billings, Texas A&M Forest Service, Bugwood.org
Blue staining fungus
The southern pine eetle is native to southern and southeastern states in the United States, as well as Central America, from Mexico to Nicaragua. In the United States, it has been found in portions of Alabama, Arkansas, Delaware, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, Arizona, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, West Virginia, Pennsylvania, and New Mexico. In recent years, the SPB has managed to expand north beyond its natural range due to warmer winters. The new range of SPB currently includes both the states of New York and New Jersey.
Map: Clarke and Nowak, 2009
The areas highlighted in red indicate the areas in which SPB are found in both North and Central America
Click here to view a map that shows the tracking of SPB invasions using detection traps into the northeastern forest of the U.S.
Southern pine beetle outbreaks can cause significant economic impacts, especially with respect to the forest industry. The timber loss in the eastern United States, due to a SPB outbreak that occurred from 1999 to 2002 was estimated to result in an economic cost of $1 billion (Clarke and Nowak, 2009). In addition, impacts specific to the saw timber and pulp industry have been significant. A study showed that short term impacts of SPB outbreak caused an average loss of $43 million per year for the timber industry, but a $30 million gain per year for wood-using firms as a direct result of the temporary surplus of timber due to increased harvest (Pye et al., 2011). The long term impacts, however, greatly outweigh the short term benefits of these types of disruption.
Photo: Ronald F. Billings, Texas A&M Forest Service , Bugwood.org
An aerial view of the devastating effects of the spread of SPB
SPB outbreaks influence the forest species composition and succession, negatively affecting the forest nutrient cycle and quality of soil due to nutrient leaching and increased erosion (Leuschner, 2006). The modifications in vegetation have implications on wildlife food resources and habitat. However, the impact on wildlife varies between positive, negative and zero net impact depending on the species and its ecological requirements (Leuschner, 2006). The gaps created in the forest pine canopy were found to be positive for the deer populations because of the increase in understory vegetation and grasses that are favoured by deer (Leuschner, 2006). However, the pine warbler has been found to be negatively impacted by the SPB as the infestation results in the destruction of the bird habitat (Tchakerian et al., 2015). The impact of the SPB on the red-cockaded woodpecker is a large concern in southern U.S. Although the impact of SPB on pine warbler and red-cockaded woodpecker are not pertinent to Canada, it is important to understand the potential impact that SPB could have on wildlife where it becomes established.
Photo: Johnny N. Dell, Bugwood.org
The southern pine beetle negatively affects the pine warbler, pictured above, by destroying the bird's habitat
In the United States, SPB outbreaks have had affected property values where pine trees and stands are located (Coulson and Meeker, n.d.). With the great loss of pine trees, SPB outbreaks have also impacted recreational use of pine forests and caused a decline in aesthetic value of pine dominated forests (Coulson and Meeker, n.d.).
To reduce the chance of attack by the SPB it is important to maintain the health of susceptible forests. To mitigate potential impacts of SPB in susceptible areas, options include:
Respond & Control
‘Salvage removal of pine trees’ may be a cost-effective option for private landowners. It is recommended to cut a buffer strip of uninfested trees when cutting currently infested trees during cut and salvage removal of pine trees. In some cases, financial return may have the potential to be great.
‘Cut and leave’ is a method to manage small areas of infested trees under warm temperature conditions. With this method, the infested trees, along with a band of uninfested trees in a designated buffer zone are cut and all are left where they were felled. Warm temperatures play a vital role in the success of this practice wherein the sun exposure overheats the beetles in felled trees. This method is typically applied during times when SPB populations are propagating, and has been extensively applied along the Gulf coast of the United States.
‘Pile and Burn’ is an effective control practice where the bark of infested trees is burned to kill any existing SPB after the felling of these infested trees.
Research for biological control is ongoing to determine what natural enemies can be used to control SPB. The checkered beetle (Thanasimus dubius) which is native to North America is one of the most studied predators of the SPB. Research into this potential biological control agent is ongoing.
Photo: John Moser, USDA Forest Service, Bugwood.org
Checkered beetle after feeding on SPB
Chemical treatments are used to manage SPB infestations in urban forests and on trees located on private property in some areas of the United States. As chemical treatment can be expensive, it may only be a suitable option to consider for high-value trees. It is important to note that some chemical treatments can protect trees for a period of time from SPB attacks, but not from blue-stain fungi, which can be damaging to the tree on its own.
In the southern United States, SPB insecticides are used as an effective method of prevention on uninfested trees of high value in recreational and residential areas. The commonly used insecticides in the southern United States contain permethrin or bifenthrin as active ingredients - both of which are registered in Canada for use in insecticides. The systemic chemicals emamectin benzoate and fipronil have shown good efficacy for high value tree protection from SPB in the United States (Billings, n.d). However, both mentioned systemic chemicals are not registered in Canada for use in insecticides.
Example Integrated Pest Management Strategy
In many cases, management of SPB occurs as follows (USDA Forest Service):
Frontalin baited traps are set during the primary dispersal phase of SPB to help predict beetle activity for that year.
Aerial surveys are conducted to detect potential SPB infestations, and locations are recorded on a GPS for mapping.
Ground crews confirm the locations of infested trees, marking the extent of the infestation
Treatments are assigned based on the data collected both aerially and confirmed on the ground level.
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Bugwood wiki. (1989). Insects and Diseases of Trees in the South. USDA Forest Service. Protrotection Report R8-PR16. 98 pp. Retrieved from http://wiki.bugwood.org/Archive:South/Dendroctonus_frontalis on 4/10/2016
Clarke, S. R. and Nowak, J. T. (2009, April). Southern Pine Beetle. Forest Insect and Disease Leaflet 49. Retrieved from http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsbdev2_042840.pdf on 4/10/2016
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Otrosina, W. J., Hess, N. J., Zarnoch, S. J., Perry, T. J., & Jones, J. P. (1997). Blue-stain fungi associated with roots of southern pine trees attacked by the southern pine beetle, Dendroctonus frontalis. Plant Disease, 81(8), 942-945.
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