A Methodology for Assessing Annual Risk of Southern Pine Beetle Outbreaks across the Southern Region Using Pheromone Traps

An operational system to forecast infestation trends (increasing, static, declining) and relative population levels (high, moderate, low) of the southern pine beetle (SPB), Dendroctonus frontalis, has been implemented in the Southern and Eastern United States. Numbers of dispersing SPB and those of a major predator (the clerid beetle, Thanasimus dubius) are monitored with multiple-funnel traps baited with the SPB aggregation pheromone frontalin and host volatiles. One to three traps are placed in each county or national forest ranger district to be surveyed for 4 consecutive weeks during the spring, to coincide with the long-range dispersal of SPB. The average number of SPB per trap per day and the ratio of SPB to total catch of SPB and clerids in the current and previous year for the same trapping location are the variables used for predicting infestation trends and population levels for the remainder of the year. An analysis of predicted and actual SPB infestation trends and population levels for 16 States and up to 19 consecutive years (1987-2005) documents the accuracy of the annual prediction system. From 1987 to 1998, predictions at the State level, validated by subsequent infestation detection records for the specific year, proved accurate 68 percent of the time (range 42 to 83 percent) for SPB infestation trend and 69 percent of the time (range 42 to 92 percent) for population level. From 1999 to 2005, the mean accuracy of predictions of SPB infestation trend improved to 82 percent for all States combined (range 71 to 100 percent); mean predictions for population level for States increased in accuracy to 74 percent (range 43 to 100 percent). Despite system limitations, forest managers have come to depend on this early warning system to predict pending outbreaks or collapses of SPB populations. This represents the first effective and validated prediction system for outbreaks of a bark beetle species.