Southern Pine Beetle Ecology: Populations within Stands

Populations of southern pine beetle (SPB) are typically substructured into local aggregations, each with tens of thousands of individual beetles. These aggregations, known as "spots" because of their appearance during aerial surveys, are the basic unit for the monitoring and management of SPB populations in forested regions. They typically have a maximum lifespan of I year, being born in the spring when dispersing SPB aggregate at points in the forest. Spots that survive to the following spring produce the dispersing beetles that form a new population of spots. SPB epidemics rise and fall with interannual variation in the number of spots within a region. Many spots, especially those that begin small, die an early death by midsummer. Others may grow throughout the summer and into the winter via a self-propagating progression of tree attacks that is critically structured by semiochemicals. Forces that influence the growth of populations within spots strongly influence the dynamic fluctuations in SPB impacts on regional forests. These forces include pine species composition, habitat edges, age and basal area of pine stands, tree defenses, the predator Thanasirnus dubins, interactions with phoretic mites and fungi, climate, and movement of beetles into and out of spots.