|CHUCHE, JULIEN - University Of Bordeaux|
|THIERY, DENIS - Institut National De La Recherche Agronomique (INRA)|
|SAUVION, NICOLAS - Institut National De La Recherche Agronomique (INRA)|
Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2016
Publication Date: 1/24/2017
Citation: Chuche, J., Backus, E.A., Thiery, D., Sauvion, N. 2017. First finding of a dual-meaning X wave for phloem and xylem fluid ingestion: characterization of Scaphoideus titanus (Hemiptera: Cicadellidae) EPG waveforms. Journal of Insect Physiology. 102:50-61.
Interpretive Summary: Over 40% of the world’s production of grape products comes from Europe, where the most important phytoplasma disease in viticulture is flavescence dorée (FD). Scaphoideus titanus, an invasive leafhopper species introduced into Europe from North America, is the vector of FD. Grapevine varieties resistant to S. titanus feeding and transmission of lethal FD must be developed, but the present inability to directly observe and measure the leafhopper’s piercing-sucking feeding in relation to transmission hampers their development. The best way to alleviate this problem is to use electropenetrography (EPG) to record S. titanus feeding. A study was conducted using DC EPG to record S. titanus feeding behaviors on grapevines, to identify waveforms and define their biological meanings. For the first time in a DC EPG study, sustained ingestion by a leafhopper was found to occur from both xylem and phloem vascular cells. Waveform C2x represented ingestion (sucking and swallowing) of xylem fluid, and two waveforms represented activities when mouthparts were inserted into phloem sieve elements: C2p-1, which may represent salivation (perhaps simultaneous with ingestion), and C2p-2, which represented active ingestion. Furthermore, an X wave, a diagnostic waveform that precedes sustained ingestion, occurred before both xylem and phloem ingestion. Such a “dual-meaning X wave” will provide insights into how the feeding tactics of S. titanus relate to other sheath-feeding hemipterans, provide support for future research to clarify the role of this leafhopper as a vector of plant pathogens, and allow future EPG studies to aid in development of grapevine varieties that resist the feeding and FD transmission caused by this insect pest.
Technical Abstract: Scaphoideus titanus, an invasive species introduced into Europe from North America, is the vector of the most important phytoplasma disease in European viticulture, flavescence dorée. In this first electropenetrography (EPG) study of S. titanus, its feeding waveforms were characterized and their biological meanings were defined. Four typical waveform phases (pathway, X wave, sustained ingestion, and interruption) and four families within those phases (A, B, C, and N) were characterized using DC EPG technology. Biological meanings for these waveforms were based on excreta pH-ingestion correlations, presence of X waves, and comparison with previous AC, DC, and AC-DC EPG waveforms conducted on Auchenorrhyncha. For the first time in DC EPG, it was observed that sustained ingestion by a deltocephaline leafhopper can occur from both xylem and phloem vascular cells. Waveform C2x represented ingestion of xylem fluid, and two waveforms represented activities when stylets were inserted into phloem sieve elements: C2p variant 1 (C2p-1), which may represent salivation (perhaps simultaneous with ingestion), and C2p variant 2 (C2p-2), which represented active ingestion. Furthermore, the X wave, which occurs prior to sustained ingestion from either phloem or xylem, was very similar in appearance to the model X wave of sharpshooters, an entirely different leafhopper subfamily, Cicadellinae. All cicadellines are obligate xylem-ingesters. Such a “dual-meaning X wave” will provide insights into how the feeding tactics of S. titanus relate to other sheath-feeding hemipterans, and will provide support for future research to clarify the role of this leafhopper as a vector of plant pathogens.