Species-specific effects of ethanol concentration on host colonization by four common species of ambrosia beetles

Authors: CAVALETTO, GIACOMO - Universita Di Padova; Ranger, Christopher; Reding, Michael - Mike; MONTECCHIO, LUCIO - Universita Di Padova; RASSATI, DAVIDE - Universita Di Padova

Submitted to: Journal of Pest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2022
Publication Date: 7/22/2022
Citation: Cavaletto, G., Ranger, C.M., Reding, M.E., Montecchio, L., Rassati, D. 2022. Species-specific effects of ethanol concentration on host colonization by four common species of ambrosia beetles. Journal of Pest Science. 96:833-843. https://doi.org/10.1007/s10340-022-01537-w.
DOI: https://doi.org/10.1007/s10340-022-01537-w

Interpretive Summary: Ethanol is emitted by trees in response to a variety of stressors and represents an important cue used by ambrosia beetles to locate suitable hosts to infest. Ethanol also favors the growth of ambrosia beetles’ nutritional fungal symbionts and suppresses the growth of antagonistic fungi. An optimal concentration of ethanol in host tissues might maximize fungal growth and offspring production, but it is unclear if this optimal concentration varies among ambrosia beetle species. To investigate this mechanism, we injected five different concentrations of aqueous ethanol solutions (5%, 25%, 50%, 75% and 90%) into the stems of container-grown oak trees. Ethanol solutions were injected every two weeks for about three months. Following the initial injections, chambers were used to confine four species of field-collected ambrosia beetles to the injected stems. Burrowing activity, ejected sawdust, gallery development, and offspring production were then quantified. The incidence of burrowing generally increased with increasing ethanol concentration for all four Scolytinae species tested. Ejected sawdust and offspring production increased with increasing ethanol concentration up to 90% for Anisandrus dispar and Xyleborinus saxesenii; by contrast, ejected sawdust and offspring production an increasing trend up to 75% ethanol followed by a decrease at 90% ethanol was associated with Xylosandrus germanus and Xylosandrus crassiusculus. Our study highlights the key role of ethanol for ambrosia beetles, and showed that the optimal concentration maximizing colonization and offspring production can vary among species.

Technical Abstract: Ethanol is emitted by trees in response to a variety of stressors and represents an important cue used by ambrosia beetles (Coleoptera; Curculionidae; Scolytinae) to locate suitable hosts to infest. Ethanol also favors the growth of ambrosia beetles’ nutritional fungal symbionts and suppresses the growth of antagonistic fungi. An optimal concentration of ethanol in host tissues might maximize fungal growth and offspring production, but it is unclear if this optimal concentration varies among ambrosia beetle species. To investigate this mechanism, we injected five different concentrations of aqueous ethanol solutions (5%, 25%, 50%, 75% and 90%) into the stems of container-grown oak trees, Quercus robur L. Ethanol solutions were injected every two weeks for about three months. Following the initial injections, modified Falcon tube chambers were used to confine four species of field-collected ambrosia beetles to the injected stems, namely, Anisandrus dispar, Xyleborinus saxesenii, Xylosandrus germanus, and Xylosandrus crassiusculus. Burrowing activity, ejected sawdust, gallery development, and offspring production were then quantified. The incidence of burrowing generally increased with increasing ethanol concentration for all four Scolytinae species tested. Ejected sawdust and offspring production increased with increasing ethanol concentration up to 90% for A. dispar and X. saxesenii; by contrast, ejected sawdust and offspring production an increasing trend up to 75% ethanol followed by a decrease at 90% ethanol was associated with X. germanus and X. crassiusculus. Our study highlights the key role of ethanol for ambrosia beetles, and showed that the optimal concentration maximizing colonization and offspring production can vary among species.