Alluring signals: the role of ethanol in attracting bark beetles to heat-stressed trees.


L. Thomas

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USDA Forest Service

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Foresters have long known that trees under stress from fire injury are vulnerable to bark beetle attacks. Rick Kelsey and Doug Westlind, researchers with the Pacific Northwest Research Station, have developed a new mechanistic model to explain how physiological changes cause heat stress in woody tissues exposed to sublethal fire temperatures and produce a chemical signal that attracts some bark beetles. When heat disrupts normal cell functions and energy production, ethanol is synthesized as a short-term survival strategy. If enough ethanol accumulates and is released to the atmosphere (mixed with resin volatiles), it becomes a strong attractant for red turpentine beetles, which target tree locations with high ethanol concentrations. Kelsey and Westlind have shown that ethanol interacts synergistically with 3-carene, a dominant ponderosa pine resin monoterpene. In a trapping study, red turpentine beetles were more attracted to lures combining ethanol and 3-carene than lures with ethanol or 3-carene alone. Understanding ecosystem responses to fire can help managers characterize forest health and plan for postfire management. The results also hold promise for developing simple ethanol detection methods for monitoring tree stress. Real-time feedback on ethanol levels could help forest managers quickly assess which trees to leave following a fire and which to cull.