Electrophysiological and behavioral responses of an ambrosia beetle to volatiles of its nutritional fungal symbiont

Authors: Ranger, Christopher; DZURENKO, MAREK - Slovak Academy Of Sciences; Barnett, Jenny; GEEDI, RUCHIKA - The Maharaja Sayajirao University Of Baroda; Castrillo, Louela; ETHINGTON, MATTHEW - Purdue University; GINZEL, MATTHEW - Purdue University; ADDESSO, KARLA - Tennessee State University; Reding, Michael - Mike

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2021
Publication Date: 3/24/2021
Citation: Ranger, C.M., Dzurenko, M., Barnett, J.L., Geedi, R., Castrillo, L.A., Ethington, M., Ginzel, M., Addesso, K., Reding, M.E. 2021. Electrophysiological and behavioral responses of an ambrosia beetle to volatiles of its nutritional fungal symbiont. Journal of Chemical Ecology. 47:463-475. https://doi.org/10.1007/s10886-021-01263-0.
DOI: https://doi.org/10.1007/s10886-021-01263-0

Interpretive Summary: Ambrosia beetles cultivate gardens of their fungal symbiont within host trees substrates as a source of nutrition on which the larvae and adults must feed. Due to this close interaction, we characterized olfactory responses of an exotic species, Xylosandrus germanus, to volatile compounds associated with its fungal symbiont Ambrosiella grosmanniae. Beetles exhibited an arrestment response to A. grosmanniae, but not to the pathogenic fungi Beauveria bassiana, Metarhizium brunneum, and Trichoderma harzianum or an agar control. Analysis of the fugnal volatile emissions identified three alcohols (i.e., 3-methyl-1-butanol, 2-phenylethanol, and 2-ethyl-1-hexanol) and one ester (i.e., methyl benzoate) in emissions from A. grosmanniae. The compound 3-methyl-1-butanol was the predominant volatile emitted from strains XgOH11 and XgVA6. Electrophysiology measurements of antennal olfactory responses determined the normalized electroantennogram (EAG) response by X. germanus was equivalent between 3-methyl-1-butanol and the positive control ethanol, but these responses were larger compared to 2-ethyl-1-hexanol, 2-phenylethanol, and methyl benzoate. During field trials, traps baited individually with 2-ethyl-1-hexanol, 2-phenylethanol, methyl benzoate, and 3-methyl-1-butanol attracted more X. germanus than a blank control, but 2-phenylethanol and 3-methyl-1-butanol also reduced attraction to ethanol. Thus, volatiles emitted by A. grosmanniae can attract X. germanus and possibly aid in developing a species-specific lure, but additional experiments are warranted to assess optimal volatile blends and release rates.

Technical Abstract: Ambrosia beetles (Coleoptera: Scolytinae) cultivate their fungal symbiont within host substrates as a source of nutrition on which the larvae and adults must feed. Due to this close interaction, we characterized short- and long-range olfactory responses of Xylosandrus germanus to volatiles associated with its fungal symbiont Ambrosiella grosmanniae. A still-air walking olfactometer was used to compare the short-range behavioral response of X. germanus to volatiles of A. grosmanniae strain XgOH11 and selected entomopathogenic fungi. Specimens exhibited an arrestment response to A. grosmanniae, but not to the entomopathogens Beauveria bassiana, Metarhizium brunneum, and Trichoderma harzianum or an agar control. Solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) identified three alcohols (i.e., 3-methyl-1-butanol, 2-phenylethanol, and 2-ethyl-1-hexanol) and one ester (i.e., methyl benzoate) in emissions from A. grosmanniae; 3-methyl-1-butanol was the predominant compound from strains XgOH11 and XgVA6. Normalized electroantennogram (EAG) depolarizations were equivalent between 3-methyl-1-butanol and the positive control ethanol, and larger compared to 2-ethyl-1-hexanol, 2-phenylethanol, and methyl benzoate. During field trials, traps baited individually with 2-ethyl-1-hexanol, 2-phenylethanol, methyl benzoate, and 3-methyl-1-butanol attracted more X. germanus than a blank control, but 2-phenylethanol and 3-methyl-1-butanol also reduced attraction to ethanol. Thus, volatiles emitted by A. grosmanniae can attract X. germanus and possibly aid in developing a species-specific lure, but additional experiments are warranted to assess optimal volatile blends and release rates.