Prescribed Fire and the Southern pine beetle

The southern pine beetle (SPB) (Dendroctonus frontalis) is one of the most destructive pests in pine ecosystems in the Southeast. For example, almost 810 million board feet of timber died during an epidemic in Texas in 1985 (Carter et al. 1991). SPB attacks the tree by boring through the bark and building galleries between the bark and wood, eventually girdling the tree. The beetles also introduce blue-stain fungi into the tree that can contribute to the death of the tree by disrupting water movement. Within the galleries, adults deposit eggs that hatch into larvae in about a week. The larvae then bore into the outer bark where they pupate. The whole cycle is completed in about 30 days and up to seven generations per year can be completed under ideal conditions.

Typically, prescribed burning is not used to directly control SPB. In the past, infected trees have been cut, piled, and burned, but this method of control is rarely used today (Swain and Remion 1981). Instead, silvicultural methods and use of resistant species are the most commonly used control methods (Belanger et al. 1993). In stands that are overstocked and under severe competition for light and nutrients, prescribed burning could be used indirectly to control SPB by removing the small, weak trees that are less resistant to beetle attack than healthier trees (Belanger and Malac 1980). Thinning the stand, either with fire or mechanical methods, creates a healthier stand that should be more resistant to beetle attack than the unthinned stand.

Prescribed burning will generally not reduce the beetles in infested stands because the beetles live underneath the bark and are protected from fire during the burn. Any fire hot enough to kill beetles would likely kill the tree as well. In addition, some species of beetles have been shown to congregate in burned areas to take advantage of trees weakened by fire (Hart 1998). It has been suggested that pest populations build up in weak trees and eventually will begin to attack nearby healthy trees (Schowalter et al. 1981). In a study after the large Florida wildfires in 1998, however, beetle populations did not appear to build up in weakened trees and attack nearby healthy trees (Hanula et al. 2002).