Southern Pine Beetle
The southern pine beetle (Dendroctonus frontalis Zimmerman) is one of the most widespread and destructive insect pests of pine. Loblolly, shortleaf, pitch, pond, and Virginia pines are the favored host tree species, although other pine trees may be susceptible during outbreaks. Tennessee’s southern pine beetle population gradually built to outbreak levels in 1998 and killed approximately 350,000 acres and $358 million of pine in the succeeding years. This mass epidemic drove pine prices down as markets were flooded with salvaged pine sawtimber and pulpwood. While this pest is native to North America, its periodic outbreaks have caused significant economic losses in Tennessee and many other states in the southern and eastern U.S.
The adult southern pine beetle is dark red-brown or black and slightly smaller than a grain of rice. Adult females initiate an attack against a suitable host tree, boring through the bark of the tree and beginning to construct an S-shaped gallery in the cambium where eggs can be laid. Males follow, being attracted to trees that have already been attacked by females. Pine trees may defend against SPB attack by exuding resin from entrance holes to attempt to flush out the beetles in “pitch tubes”. If a tree is weakened or if the population of SPB is high enough, the beetles are able to overcome this tree defense and infest the tree.
Eggs laid by the females within the tree hatch, and the newly hatched larvae continue to tunnel within the vascular cambium until they have developed and are prepared to pupate. New adults then exit the tree through small, round holes in the bark and fly to attack new trees. Beetles can also inoculate the tree with bluestain fungi which damages the sapwood. This fungus, coupled with the construction of the galleries girdles the tree and leads to eventual tree mortality.
Symptoms of southern pine beetle attack include the presence of pitch tubes along the trunk on the outside of the bark. The tree crown will begin to fade, turn red or needles fall off once galleries within the cambium begin to girdle the tree. Additionally, presence of small round exit holes may be visible in the bark, which often becomes loose and easily peels off. Bark that has peeled off the tree may show the S-shaped galleries of SPB beneath the bark, which can be another characteristic sign of SPB.
Since 2003, southern pine beetle populations in Tennessee have declined as availability of host species is low and populations of predator clerid beetles are high. Regionally, only a handful of states are seeing spotty southern pine beetle infestations which can be easily managed. However, due to the cycles of outbreaks that SPB populations typically take, monitoring for SPB populations is conducted annually to provide early information on potential future outbreaks.
Four Tennessee counties are surveyed annually using pheromone baited traps. The samples collected from these traps are analyzed and the resulting data is entered into a monitoring portal which is shared by a number of states across the region. Research evaluating population dynamics of southern pine beetle and its primary predatory, the clerid beetle Thanasimus dubius, found the number and ratio of SPB and the clerid beetle could be used to predict population spikes of SPB and give an early indication of potential outbreaks. The collaborative surveying and monitoring effort helps managers and researchers track southern pine beetle movement and assess future risk.
The southern pine beetle is predominately attracted to stands of pine that are stressed in some way. Drought and overcrowding are the two most common stressors that impact tree health. Proper forest management and timely thinnings or harvests are the best management options to protect pine stands against the southern pine beetle. For more information on management options and financial assistance opportunities through Tennessee Department of Agriculture, Division of Forestry, please follow this link: Southern Pine Beetle Cost Share for Landowners (tn.gov).
If an infestation does occur in your pine stand, options for management include cut & remove, cut & leave, cut & hand spray, pile & burn, or aerial pesticide applications. While these options are available when an outbreak occurs, the most effective means to prevent SPB from reducing the value of pine stands is to proactively manage pine stands to reduce the susceptibility to SPB.
What Can You Do?
In general, following practices that improve pine health, whether for single pine trees or for entire pine forests, can reduce susceptibility to SPB. Correct tree spacing, timely thinnings, and clean harvesting can prevent southern pine beetle populations from building.
Learn to recognize the signs and symptoms of an infestation and contact your county agent, professional forester, or the Division of Forestry with suspected SPB activity. Early detection is very important to preventing or mitigating major outbreaks.