Biological Control of Southern Pine BeetleThis article is part of a larger document. View the larger document here.
Exotic invasive forest insects are frequently managed through classical biological control, which involves searching for, introducing, and establishing their exotic natural enemies. Biological control of native bark beetles, including the southern pine beetle (SPB), has been primarily attempted by conserving and manipulating their natural enemies. Knowledge of the role and biology of SPB natural enemies is increasing but is still limited, and is rarely well connected to coincident estimates of SPB host density. A rich complex of SPB native natural enemies exists, and these are discussed in greater detail in other chapters in this book. The cryptic nature of Dendroctonus species within phloem and bark, combined with the properties of many natural enemies (small size, highly aggregated distribution, lower density than their prey, and often acting late in the beetle’s life cycle), results in challenging sampling problems that are difficult to overcome. Attempts to assess impact of natural enemies have often been presented as percent of mortality, but rarely do these assessments show variation in mortality. The manner in which mortality varies with host density is important in population regulation. Predators, parasitoids, and competitors of the SPB respond in varying degrees to SPB pheromones and tree volatiles during host selection. Variables such as bark thickness and SPB density influence parasitoid success. In making oviposition choices, parasitoids tend to select the host beetle and tree species from which they emerged. Short SPB generation times, continuous flight, and attack by SPB adults result in infestations containing all life stages of beetles and natural enemies. Opportunities for numerical response of parasitoids to epidemic population growth should be great but have not been confirmed. Manipulation efforts indicate that providing nutrients for parasitoid adults increases their longevity, stimulates production of additional eggs, and prevents resorption of existing eggs. Parasitoids do forage in canopies of both pine and hardwood trees, possibly to acquire honeydew as adult nutrition. Predators frequently are the most abundant and visible sources of SPB mortality, and their potential role as delayed density-dependent agents may be important in the cycles exhibited by SPB populations. Simulation models that experimentally remove mortality attributable to natural enemies show how rapidly infestations grow when natural enemies are absent. Experimental research on Monochamus spp. indicates that they can cause high mortality to SPB brood as competitors and predators, and field observations suggest that they may play an important role in the collapse of SPB epidemics.