Endemic and Epidemic Populations of Southern Pine Beetle: Implications of the Two-Phase Model for Forest Managers

Abstract

Abstract Typical of many Dendroctonus species, the southern pine beetle (D. frontalis Zimmerman) exhibits dramatic fluctuations in population levels. Using field observations of beetle damage, this study empirically demonstrates that a two-phase model described for mountain pine beetle (D. ponderosae Hopkins) is appropriate for southern pine beetle at each of five hierarchical levels: the tree, the local infestation, the county, the state, and the region. The model has three points that represent a stable low-level (endemic) phase maintained by host-tree-defensive capabilities, a transient high-level (epidemic) phase determined by the availability of host material, and a threshold between the two phases. The threshold depends on local environmental and biotic factors and is a rarely observed phenomenon. Implications of these results for southern pine beetle management and control are discussed. The necessity for establishing and maintaining control programs during the endemic phase is stressed. For. Sci. 35(4): 1075-1087.