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United States Department of Agriculture

Agricultural Research Service

Title: Stylet Penetration by Adult Homalodisca Coagulata on Grape: Electrical Penetration Graph Waveform Characterization, Tissue Correlation, and Possible Implications for Transmission of Xylella Fastidiosa

Authors
item Backus, Elaine
item Habibi, Javad - UNIV OF MO-COLUMBIA
item Yan, Fengming - PEKING UNIV-BEIJING,CHINA
item Ellersieck, Mark - UNIV OF MO-COLUMBIA

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 6, 2005
Publication Date: November 1, 2005
Citation: Backus, E.A., Habibi, J., Yan, F., Ellersieck, M. 2005. Stylet Penetration by Adult Homalodisca coagulata on Grape: Electrical Penetration Graph Waveform Characterization, Tissue Correlation, and Possible Implications for Transmission of Xylella fastidiosa. Annals of the Entomological Society of America. 98(6):787-813.

Interpretive Summary: The glassy-winged sharpshooter (GWSS) is an exotic vector of the Pierce's Disease (PD) bacterium that was introduced to California in the early 1990's. It has since greatly increased the threat of PD to the grape industry, as well as stone fruit, nursery and ornamental industries in California. This is the first in a series of papers that, taken together, will answer fundamental questions about how sharpshooter feeding controls transmission of the bacterium. Ultimately, we will use this information to develop a Stylet Penetration Index, for screening crop varieties for resistance to the vector's ability to transmit the PD bacterium. In this paper, we categorized, characterized and partially defined the electrical penetration graph (EPG) waveforms from GWSS stylet penetration on susceptible grape petiole. Also, for the first time in any EPG study of leafhopper or planthopper feeding, we demonstrate through case studies of individual probes how to follow the process of stylet penetration step-by-step as it is occurring. Finally, we discuss the implications of our findings for understanding the transmission mechanism of Xylella, in comparison with hypothesized mechanisms in the literature.

Technical Abstract: The glassy-winged sharpshooter (GWSS), Homalodisca coagulata (Say), is an exotic vector of the Pierce's Disease (PD) bacterium, Xylella fastidiosa (Wells et al), that was introduced to California in the early 1990's. It has since greatly increased the threat of PD to the grape industry, as well as stone fruit, nursery and ornamental industries in California. This is the first in a series of papers that, taken together, will answer fundamental questions about how sharpshooter feeding controls transmission of Xylella. Ultimately, we will use this information to develop a Stylet Penetration Index, for screening crop varieties for resistance to the vector's ability to transmit the PD bacterium. In this paper, we categorized and characterized electrical penetration graph (EPG) waveforms from GWSS stylet penetration on susceptible grape petiole, paying special attention to waveform fine structures that are likely to be the key to detecting the instant of inoculation. We also performed the first half of the standard "triangle of correlation" studies to define the biological meanings of these waveforms. Also, for the first time in any EPG study of leafhopper or planthopper feeding, we demonstrate through case studies of individual probes how to follow the process of stylet penetration step-by-step as it is occurring, including salivary sheath branching and, in some cases, the instant when the stylets first puncture a xylem cell. Finally, we discuss the implications of our findings for understanding the transmission mechanism of Xylella, in comparison with hypothesized mechanisms in the literature.

Last Modified: 9/10/2014
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