Ubiquitous volatile compound facilitates efficient host location by a non-native ambrosia beetle

Authors: Ranger, Christopher; TOBIN, PATRICK - Forest Service (FS); Reding, Michael - Mike

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2014
Publication Date: 7/25/2014
Publication URL: http://handle.nal.usda.gov/10113/59738
Citation: Ranger, C.M., Tobin, P., Reding, M.E. 2014. Ubiquitous volatile compound facilitates efficient host location by a non-native ambrosia beetle. Biological Invasions. DOI: 10.1007/s10530-014-0758-2.

Interpretive Summary: Many non-native ambrosia beetles attack physiologically-stressed trees. In response to many sources of stress, trees emit ethanol, which is used by certain ambrosia beetles to find vulnerable trees. Because stressed trees can be sparse within a landscape, we sought to assess the role of ethanol as an attractant for ambrosia beetles to efficiently locate trees for colonization. We conducted a series of experiments and observed that attacks occurred on trees baited with ethanol, but ceased upon removal of the ethanol cue. Ambrosia beetles also located and attacked trees injected with ethanol, but rarely landed on and never attacked neighboring trees not emitting ethanol. A spatial analysis of ambrosia beetle attacks within ornamental nurseries revealed that only certain host species or cultivars, and only certain individuals within these host species or cultivars, were attacked. Our analyses also detected ethanol in trees attacked within the ornamental nurseries, but not in non-attacked trees. Thus, certain ambrosia beetles use a sophisticated olfactory mechanism to navigate over diverse landscapes and specifically locate trees associated with the emission of ethanol. This phenomenon appears to be governed by the ratio of ethanol to other general odor components that signify a host in a vulnerable physiological condition. Because a variety of abiotic and biotic stressors induce the emission of ethanol by trees, X. germanus could serve as an important bioindicator of tree health in natural and managed ecosystems.

Technical Abstract: Xylosandrus germanus (Blandford) is a polyphagous exploiter of physiologically-stressed trees. In response to many sources of stress, trees emit ethanol, which represents an important host-selection cue for X. germanus adults. Because stressed trees can be spatially and temporally variable over a landscape, we sought to assess the role of ethanol as a primary attractant for X. germanus in efficiently locating trees for colonization. We conducted a series of field-based experiments and observed that attacks occurred on trees baited with ethanol, but ceased upon removal of the ethanol cue. Xylosandrus germanus also located and attacked ethanol-injected trees, but rarely landed on and never attacked neighboring trees not emitting ethanol. A spatial analysis of ambrosia beetle attacks within ornamental nurseries revealed that only certain host species or cultivars, and only certain individuals within these host species or cultivars, were attacked; ethanol was detected by SPME-GC-MS in the attacked trees, but not in non-attacked trees. Thus, X. germanus uses a sophisticated olfactory mechanism to navigate over diverse landscapes and specifically locate trees associated with the emission of ethanol, and appears to be governed by the ratio of ethanol to other general odor components that signify a host in a vulnerable physiological condition. Because a variety of abiotic and biotic stressors induce the emission of ethanol by trees, X. germanus could serve as an important bioindicator of tree health in natural and managed ecosystems.