Freeze stress of deciduous trees induces attacks by opportunistic ambrosia beetles

Authors: Ranger, Christopher; SCHULTZ, PETER - Virginia Polytechnic Institution & State University; FRANK, STEVEN - North Carolina State University; Reding, Michael - Mike

Submitted to: Agricultural and Forest Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2018
Publication Date: 12/13/2018
Citation: Ranger, C.M., Schultz, P.B., Frank, S., Reding, M.E. 2018. Freeze stress of deciduous trees induces attacks by opportunistic ambrosia beetles. Agricultural and Forest Entomology. 21(2):168-179. https://doi.org/10.1111/afe.12317.
DOI: https://doi.org/10.1111/afe.12317

Interpretive Summary: Ambrosia beetles (Curculionidae: Scolytinae) are among the most destructive insects of ornamental and horticultural trees. Despite a broad host tree range, several species of ambrosia beetles attack living but weakened trees emitting stressed induced ethanol. Our current study sought to assess the capability of freeze stress to induce attacks by ambrosia beetles, and to characterize the emission of ethanol from freeze-stressed trees. Freeze stress was imposed by holding container grown trees overnight at -10°C in temperature controlled chambers. Field experiments were then conducted that allowed ambrosia beetles to freely choose between freeze-stressed and uninjured control trees. Freeze stress predisposed the thin-barked deciduous trees to attack, while no attacks were observed on untreated control trees. Trees were rapidly attacked, with attacks often being initiated 1-2 days after imposing freeze stress. Ethanol emissions from tree stems were detected at 1 day after imposing freeze stress, and peaked 4 days after injury. Our current study demonstrates non-native ambrosia beetles preferentially attack freeze-stressed trees. Trees growing in ornamental nurseries and tree fruit orchards with an intolerance of freeze stress are predicted to be vulnerable to attack when subjected to mild winter temperatures followed by late-spring freezes.

Technical Abstract: Ambrosia beetles (Curculionidae: Scolytinae) are among the most destructive insects of ornamental and horticultural trees. Despite a broad host tree range, several species in the tribe Xyleborini exhibit a narrow preference for living but weakened trees emitting stressed induced ethanol. Our current study sought to assess the capability of freeze stress to induce attacks by Xyleborini ambrosia beetles, and to characterize the emission of ethanol from freeze-stressed trees. Freeze stress was imposed by holding container grown trees overnight at -10°C in temperature controlled chambers. Field experiments were then conducted that allowed ambrosia beetles to freely choose between freeze-stressed and uninjured control trees. Freeze stress predisposed the thin-barked deciduous trees Cercis canadensis L., Cornus florida L., Malus pumila Mill., and Styrax japonicus Sieb. to attack, while no attacks were observed on untreated control trees. Xylosandrus germanus (Blandford) was the predominant species recovered from freeze-stressed trees deployed in Ohio, USA, while Xylosandrus crassiusculus (Motschulsky) was the predominant species recovered in Virginia, USA. Trees were rapidly attacked, with attacks often being initiated 1-2 days after imposing freeze stress. Ethanol emissions from stems of S. japonicus were detected by SPME-GC-MS at 1 day after imposing freeze stress, and peaked 4 days after injury. Our current study demonstrates non-native ambrosia beetles preferentially attack freeze-stressed trees. Trees growing in ornamental nurseries and tree fruit orchards with an intolerance of freeze stress are predicted to be vulnerable to attack when subjected to mild winter temperatures followed by late-spring freezes.