Differential selection behavior of southern pine beetle (Dendroctonus frontalis) and primary predator, Thanasimus dubius to α-pinene enantiomers

Each spring, state and federal agencies monitor southern pine beetle (SPB) populations by baiting funnel traps with frontalin (an SPB aggregate lure) and α-pinene (a host monoterpene) to collect SPB and their primary predator, a clerid beetle, Thanasimus dubius. The ratio of the average number of collected SPB to T. dubius acts as a predictive model; forecasting SPB population levels and trends for the current year. Previous studies suggest that both SPB and T. dubius do not differentiate between frontalin enantiomers. However, it is unknown whether SPB or T. dubius differentiate between α-pinene enantiomers, and the chirality of α-pinene is (host) species dependent. The objective of this study was to determine whether SPB or T. dubius differentiate between α-pinene enantiomers.

In 2011, we conducted field trials using (+) α-pinene, (-) α-pinene, (+/-) α-pinene, (+/-) α-pinene of double volume, and an unbaited control. To ensure SPB and clerid captures, frontalin and endo-brevicomin (recently recognized as an SPB aggregant at 6m) were included with each α-pinene treatment. Field trials were conducted in both spring and fall in loblolly pine stands in Oconee National Forest, Georgia. Preliminary results indicate increased SPB captures in the springtime and high numbers of T. dubius captured in the fall. Traps baited with (+) α-pinene captured a greater number of SPB than traps baited with only (-) α-pinene; whereas, approximately equal numbers of T. dubius were captured in traps baited with either pure or racemic α-pinene enantiomers. By increasing our knowledge of the differential sensitivity of SPB and T. dubius to pure or racemic α-pinene enantiomers, we may be able to improve the accuracy of SPB monitoring programs, and our understanding of the significance of enantiomer composition in SPB host selection behavior.