Host selection, oviposition and feeding by a phytopathogen vector, Diaphorina citri (Hemiptera: Liviidae), modulated by plant exposure to formic acid

Authors: GEORGE, JUSTIN - University Of Florida; Shi, Qingchun; STELINSKI, LUKASZ - University Of Florida; Stover, Eddie; Lapointe, Stephen

Submitted to: Frontiers in Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2019
Publication Date: 3/29/2019
Citation: George, J., Shi, Q., Stelinski, L., Stover, E.W., Lapointe, S.L. 2019. Host selection, oviposition and feeding by a phytopathogen vector, Diaphorina citri (Hemiptera: Liviidae), modulated by plant exposure to formic acid. FRONTIERS IN ECOLOGY AND EVOLUTION. 7:78. https://doi.org/10.3389/fevo.2019.00078.
DOI: https://doi.org/10.3389/fevo.2019.00078

Interpretive Summary: Plants produce a wide range of odors, some of which degrade in air. Citrus odors and their breakdown products, such as formic and acetic acids, are involved in the process of host finding by Asian citrus psyllids, a devastating pest of citrus throughout the world. Formic acid causes psyllids to increase their attempts to feed. This study investigated how exposure of citrus plants to formic acid changed the odors emitted by the plants and modified psyllid behavior. Volatilized formic acid caused a large increase in release of citrus odors by the plants, attracted psyllids and increased egg-laying.

Technical Abstract: Citrus volatiles and their breakdown products, such as formic and acetic acids, guide host finding by Asian citrus psyllids (ACP). Formic acid elicits psyllid antennal responses and stimulates ACP probing. This study investigated how exposure to vapor phase formic acid induced plant defenses in Citrus macrophylla and modified psyllid host finding. Chemical analyses of headspace volatiles and behavioral assays were performed before and after exposure of ACP susceptible and resistant plants to vapor phase formic acid. Real time-quantitative polymerase chain reaction (RT-qPCR) elucidated changes in plant defense-associated gene expression following exposure. Electrical Penetration Graph (EPG) recordings measured changes in ACP feeding behavior on citrus with and without exposure to formic acid. Volatilized formic acid caused a 200-500% increase in release of citrus volatiles 1-3 hours after exposure, increased attraction of ACP to Poncirus trifoliata (resistant to ACP) and increased oviposition compared with controls. RT-qPCR showed significant increases in expression of WRKY22, GST1, RAR1 and EDS1 genes following exposure that also reduced phloem, but not xylem, ingestion by adult ACP. Formic acid, produced directly or as a degradation product of common citrus volatiles, induced plant defenses and activated volatile release that modified host finding and feeding behaviors of an important phytopathogen vector.