The following is a brief overview of the southern pine beetle (SPB) and the context of its status as a forest and shade-tree pest. Additional and more detailed information is available through the links provided on the SPB main page.
SPB is one of five common species of pine bark beetles that occur throughout the Southeastern United States. Pine bark beetles utilize stressed, dying or recently dead pines as hosts. All species tunnel, reproduce and feed in the inner bark or phloem (located between the outer bark and the wood); this activity disables the transport of sugars through the tree. In addition, several bark beetle species (including the SPB) introduce a blue-stain fungus into the wood, plugging the tree's water transport system. Typically, pines successfully colonized by SPB are functionally dead within one day after attack, despite the fact that the crown may retain green needles for several days or weeks.
Why be concerned about beetles that kill trees that are already weakened and dying anyway? Indeed, bark beetles are generally scavengers just doing their ecological job of recycling scattered, stressed-out pines (those weakened by old age, injury, competition with other plants, etc.) into organic material, and the SPB is generally restricted to such trees when their populations are low. Due to their remarkable reproductive capacity and odor-driven communication system, however, SPB populations can rapidly build and spread through pine forests or landscapes under certain environmental conditions, mass-attacking even healthy trees. Groups or "spots" of SPB-infested trees can enlarge by more than 50 feet per day, quickly resulting in multiple acres of dead pines. This can result in substantial economic, aesthetic, recreational, ecological and other types of losses. During one of Florida's worst SPB years on record (2001), there were over 2,900 infestations and 17,600 acres of killed timber statewide. Furthermore, because the SPB is no respecter of property boundaries, one landowner's timber infestation can easily become an adjacent neighbor's residential shade-tree nightmare, or vice versa.
Any number of factors that stress, weaken or injure pines can increase their susceptibility to SPB attack, population buildup, and damage. Some of these factors, such as severe droughts or damaging storm events, are periodical environmental occurrences over which we typically have no control. Many other stress factors, however, are within humankind's ability to manipulate, and indeed have been created by our own mismanagement of the forest over both the short and long term. Some of these factors include:
Although SPB populations naturally fluctuate according to environmentally-driven cycles, these human-induced factors increase the severity, frequency, and extent of SPB outbreaks and infestations.
The best way to help prevent SPB infestations is to manage pine forests, woodlots and residential shade trees in ways that keep them healthy, vigorous and resistant to attack. These practices include:
There are many reasons why pine trees die; therefore, one should not assume that every circumstance of dying or declining pines is the result of an SPB infestation. There are other species of bark beetles that cause symptoms similar to those caused by the SPB, but infestations by these less-aggressive beetles are not as critical to control; with such species sometimes the best approach is to do nothing and let the infestation die out on its own. Thus, before jumping to the conclusion that SPB is the culprit, the existence of suspicious pine mortality should be reported to a Florida Forest Service forester or county extension agent, who can evaluate the situation and recommend a course of action.
If dying or declining pines are positively identified as infested with SPB, the best means of control is to promptly cut and remove the trees to avoid beetle spread to adjacent living trees. In forests, a buffer strip of uninfested green trees is also cut and removed to ensure the infestation has been completely eradicated. Other control strategies (e.g., cutting and burning/burying infested trees, felling and leaving infested trees in remote forest areas) may be warranted in special circumstances where cut-and-remove is not feasible.
One historical control option that is currently not available is the cut-and-spray technique. This technique involves felling infested trees into workable log sections and thoroughly spraying the bark with an insecticide. The insecticides historically used for this purpose (e.g., lindane and chlorpyrifos), however, are no longer registered for such use, and replacement chemicals have not been developed. Certain restricted-use pesticides (e.g., synthetic pyrethroids) may be registered for use as a preventive spray on uninfested landscape trees, but homeowners should carefully investigate and evaluate the costs and benefits of their use. These products are probably most appropriate for protection of very high value trees adjacent to SPB-infested trees that cannot be cut and removed. The Florida Forest Service forest entomologist or a county extension office can be consulted for advice.
In conclusion, it is important to remember that the SPB is a native insect and a natural part of the pine forests of the Southeast. When its populations are at low (endemic) levels, it is usually not much of a problem. Periodic SPB outbreaks have been so destructive largely because we as a people have created widespread forest conditions that foster SPB outbreaks. If we really want to lessen the impact of insects like the SPB, it will be through practicing proactive, prevention-focused management of our forests and shade trees, rather than a reactive, control-focused response to existing pest problems.