ARS | Publication request: The Sharpshooter X-wave: Correlation of xylem penetration by glassy-winged sharpshooter with an electrical penetration graph (EPG) waveform

Submitted to: XXI International Congress of Entomology, Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 14, 2008
Publication Date: July 6, 2008
Citation: Backus, E.A., Holmes, W., Reardon, B., Schreiber, F., Walker, G. 2008. The Sharpshooter X-wave: Correlation of xylem penetration by glassy-winged sharpshooter with an electrical penetration graph (EPG) waveform [abstract no. 1597]. In: Proceedings of the XXIII International Congress of Entomology held in Durban, South Africa, July 6-12, 2008.

Technical Abstract: Electrical penetration graph (EPG) monitoring is a rigorous means of observing and quantifying the feeding of any piercing-sucking insect. Previous studies with aphid and leafhopper pests of agricultural crops have demonstrated the unique value of what is termed the X wave, i.e. the waveform that represents first penetration of the insect’s piercing-sucking mouth parts, the stylets, into a preferred vascular tissue for ingestion, usually a phloem sieve element or xylem tracheary element. This paper presents the first direct evidence of the sharpshooter X wave, as studied in glassy-winged sharpshooter, Homalodisca vitripennis, and smoke tree sharpshooter, H. liturata (Hemiptera: Cicadellidae). We observed the consistent association of the X wave with salivary sheath termini in a xylem cell, especially mature (lignified), secondary xylem cells. The X wave is a complex, multi-component waveform family that is composed of waveform types B1s (previously shown to represent precibarial valve movement and possible egestion), B1w (salivation), proto-C (possible micro-ingestion) and C (macro-ingestion/ cibarial pumping). The X wave is a pathway- and interruption-phase waveform that is best visualized using the AC-DC EPG monitor, with input impedance set at 10E7 Ohms, to balance emf and R components. The sharpshooter X wave is correlated with first penetration of xylem, and represents a suite of behaviors that we propose function to: 1) physically seal stylet tips into the cell via sheath salivation, 2) taste constituents of the cell to determine acceptability, and 3) mechanically test strength of the stylet seal via trial cibarial pumping. We hypothesize that the X wave is associated with behaviors that control inoculation of Xylella fastidiosa.