Freeze stress of deciduous trees induces attacks by opportunistic ambrosia beetles

A broad host range and the utilization of living but weakened trees contribute, in part, to the invasion success of ambrosia beetles (Curculionidae: Scolytinae). The present study assessed the capability of freeze stress to induce attacks by ambrosia beetles. Freeze stress predisposed Cercis canadensis L., Cornus florida L., Malus pumila Mill. and Styrax japonicus Sieb. to attack under field conditions, although no attacks occurred on untreated trees. More attacks occurred on freeze-stressed versus flood-stressed M. pumila in Virginia but not for S. japonicus in Ohio. Attacks on flooded trees were skewed towards the base of the trunk, whereas attacks on freeze-stressed trees mainly occurred around the upper regions of the trunk and into the branches. The predominant species recovered were Anisandrus maiche Stark and Xylosandrus germanus (Blandford) in Ohio, and Xylosandrus crassiusculus (Motschulsky) in Virginia. Ethanol emissions from trunks of S. japonicus were detected by solid phase microextraction-gas chromatography-mass spectrometry at 1 day after imposing freeze stress, peaking 4 days after injury. Trees with an intolerance of freeze stress are predicted to be vulnerable to attack, especially when subjected to mild winter temperatures followed by late-spring freezes. Freeze stress could thereby facilitate the destructiveness of exotic ambrosia beetles.