Ambrosia beetle response to ethanol concentration and host tree species

Authors: CAVALETTO, GIACOMO - University Of Padua; FACCOLI, MASSIMO - University Of Padua; Ranger, Christopher; RASSATI, DAVIDE - University Of Padua

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2021
Publication Date: 5/5/2021
Citation: Cavaletto, G., Faccoli, M., Ranger, C.M., Rassati, D. 2021. Ambrosia beetle response to ethanol concentration and host tree species. Journal of Applied Entomology. 145(8):800-809. https://doi.org/10.1111/jen.12895.
DOI: https://doi.org/10.1111/jen.12895

Interpretive Summary: Ethanol emitted by stressed trees is used by ambrosia beetles to locate susceptible hosts to colonize. Ethanol also enhances the growth of ambrosia beetles' nutritional fungal symbionts and improves colonization success of beetles. Whether host selection and colonization are affected also by the amount of ethanol produced and emitted by stressed trees and by tree species is still unclear. To investigate these mechanisms, we induced attacks by ambrosia beetles in bolts of eight tree species by coring and filling them with two ethanol-water solutions containing 5% and 90% ethanol. Entry holes were used as a proxy for host selection whereas gallery development stage was used as a proxy for colonization success. Ethanol concentration differentially affected host selection of the three ambrosia beetles that were active during this study. Anisandrus dispar preferentially attacked bolts with 90% ethanol concentration, Xylosandrus crassiusculus preferentially attacked bolts with 5% ethanol concentration, and Xyleborinus saxesenii attacked bolts irrespective of ethanol concentration. Colonization success of X. crassiusculus reflected the same pattern observed for entry holes. The effect of host tree species was most prominent for X. saxesenii, while X. crassiusculus established a higher number of developed galleries in Ostrya carpinifolia bolts than on five of the other tested tree species. Our results support the potential role of ethanol concentration and host tree species in determining the ecological niche of different ambrosia beetle species. These results will also help to improve management tactics by understanding the interactions between ethanol, tree health, and ambrosia beetle colonization success.

Technical Abstract: Ethanol emitted by stressed trees is an olfactory cue used by ambrosia beetles (Coleoptera; Curculionidae; Scolytinae) to locate susceptible hosts to colonize. In addition, ethanol enhances the growth of ambrosia beetle fungal symbionts, improving colonization success. Whether host selection and colonization are affected also by the amount of ethanol produced and emitted by stressed trees and by tree species is still unclear. To investigate these mechanisms, we induced attacks by ambrosia beetles in bolts of eight tree species by coring and filling them with two ethanol-water solutions containing 5% and 90% ethanol. For each ethanol concentration, bolts of the eight different tree species were replicated 6 times in a randomized complete block design. Entry holes were used as a proxy for host selection whereas gallery development stage was used as a proxy for colonization success. Ethanol concentration differentially affects host selection of the three ambrosia beetles that were active during this study. Anisandrus dispar Fabricius preferentially attacked bolts with 90% ethanol concentration, Xylosandrus crassiusculus (Motschulsky) preferentially attacked bolts with 5% ethanol concentration, and Xyleborinus saxesenii (Ratzeburg) attacked bolts irrespective of ethanol concentration. Colonization success of X. crassiusculus reflected the same pattern observed for entry holes. The effect of host tree species was most prominent for X. saxesenii, while X. crassiusculus established a higher number of developed galleries in Ostrya carpinifolia Scopoli bolts than on five of the other tested tree species. Our results support the potential role of ethanol concentration and host tree species in determining the ecological niche of different ambrosia beetle species.