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Title: Formic and acetic acids in degradation products of plant volatiles elicit olfactory and behavorial responses from an insect vector

Author
item George, Justin
item Robbins, Paul
item Alessandro, Rocco
item STELINSKI, LUKASZ - University Of Florida
item Lapointe, Stephen

Submitted to: Chemical Senses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2016
Publication Date: 2/8/2016
Citation: George, J., Robbins, P.S., Alessandro, R.T., Stelinski, L.L., Lapointe, S.L. 2016. Formic and acetic acids in degradation products of plant volatiles elicit olfactory and behavorial responses from an insect vector. Chemical Senses. 41(4):325-338.

Interpretive Summary: The Asian citrus psyllid transmits the bacterial disease of citrus known as citrus greening disease, a major threat to citrus industry worldwide. We studied antennal and behavioral responses of adult psyllids to odors of young citrus leaves. Individual compounds were identified and confirmed by recordings of antennal responses to compounds loaded into glass stimulus tubes. Tubes loaded with ß-ocimene or citral produced no antennal response immediately after preparation at a range of concentrations. The same tubes became stimulatory after 3 to 9 days at room temperature. We demonstrated that both compounds degraded completely to acetaldehyde, acetone, acetic acid, formic acid and other compounds. Two of the degradation products produced consistent and large antennal responses from the psyllid and these were identified as acetic and formic acids. Both were highly stimulatory to psyllid antennae and responses were correlated with dose. Feeding behavior of the psyllid was studied by incorporating blends of citrus odors in varying proportions and amounts into a wax product. More attempts to feed were observed on this wax containing blends of acetic and formic acids compared with either acid separately or other compounds. Our study suggests that the Asian citrus psyllid may use degradation products for host finding and may orient to formic and acetic acid present in the citrus tree canopy. These observations of antennally active compounds, both constitutive and arising as degradation products from constitutive plant volatiles, may contribute to development of attractants and/or repellants for this important species.

Technical Abstract: The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae) vectors the bacterial pathogen presumed to be the etiological agent of citrus greening disease, Huanglongbing (HLB), a major threat to citrus industry worldwide. We studied antennal and behavioral responses of Diaphorina citri to principal components of headspace volatiles collected from young citrus leaves (flush). Candidate compounds identified by gas chromatograph-coupled electroantennogram (GC-EAD) were confirmed by antennal responses to neat compounds loaded into glass stimulus tubes. Tubes loaded with ß-ocimene or citral produced no antennal response immediately after preparation at a range of concentrations. The same tubes became stimulatory after 3 to 9 days at room temperature. Gas chromatography-mass spectroscopy (GC-MS) demonstrated that both compounds degraded completely over 3 to 9 days in glass (with or without filter paper) to acetaldehyde, acetone, acetic acid, formic acid and other compounds. GC-EAD of extracts of filter paper loaded with neat compounds aged 3 to 9 days in glass pipettes identified two peaks that elicited consistent and large antennal responses; these were identified by GC-MS as acetic and formic acids. Both acids were highly stimulatory to D. citri antennae and responses were correlated with log dose. Probing behavior of D. citri was studied by incorporating blends of citrus volatile compounds in varying proportions and amounts into an emulsified wax substrate (SPLATTM, ISCA Technologies, Inc). More probes were observed on SPLAT containing blends of acetic and formic acids compared with either acid separately or other compounds. Our study suggests that phytophagous insects may use degradation products for host finding and that D. citri may orient to formic and acetic acid present in the citrus tree canopy. These observations of antennally active compounds, both constitutive and arising as degradation products from constitutive plant volatiles, may contribute to development of attractants and/or repellants for this important species.