Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 9/4/2007
Publication Date: 12/12/2007
Citation: Backus, E.A. 2007. Feeding Behaviors of the Glassy-Winged Sharpshooter that Control Inoculation of Xylella fastidiosa. In: Proceedings of the 2007 Pierce's Disease Research Symposium, December 12-14, 2007, San Diego, California. p. 116-119
Interpretive Summary: Specific stages in the feeding of the glassy-winged sharpshooter (GWSS) on plants were studied by recording changes in electrical waveforms occurring during those stages. Both ingestion and egestion feeding behaviors were identified, as well as the mechanism of inoculation of Xylella fastidiosa. Objective 1 successfully showed that ingestion is represented by waveform C, which nearly always occurs in a xylem cell. GWSS virtually never ingests from non-xylem cells while on susceptible grape. Objective 2 showed that the B1s waveform represents muscular fluttering of a valve in the anterior foregut of the insect, and that the B1w waveform represents salivation. In addition, Objective 3 of this work identified a unique combination waveform, the sharpshooter X-wave, which incorporates the B1w, B1s, other waveforms to be discussed, and a short C waveform event. Results discussed support that the B1s and B1w of the X-wave represent egestion (expulsion) of fluids from the insect’s anterior foregut into a xylem cell, and likely represent the instant that cells are inoculated. Identification of the mechanism of inoculation, and the EPG waveforms that represent it, will allow development of novel means of screening crop plants for resistance to Xylella fastidiosa inoculation using EPG.
Technical Abstract: In the final eight months of this grant, we completed remaining studies and emphasized writing results for publication. Overall, all objectives of this grant were successfully completed. The work identified the electrical penetration graph (EPG) waveforms responsible for both ingestion and egestion by the glassy-winged sharpshooter (GWSS), and provided evidence that the mechanism of inoculation of Xylella fastidiosa is a combination of egestion and salivation. Objective 1 successfully showed that ingestion is represented by the EPG waveform C, which nearly always occurs in some type of xylem cell. Earliest events of waveform C (usually short in duration) often occur in non-functional, primary xylem, whereas later events (longer in duration) always occur in lignified, presumably functional, secondary xylem. GWSS virtually never ingests from non-xylem cells while on susceptible grape. Objective 2 showed that the B1s waveform is correlated with muscular fluttering of the precibarial valve, and that the B1w waveform represents salivation. These waveforms occur throughout the pathway phase of feeding, thus occur in all cell types that are penetrated. During Objective 3 work, several experiments with both GWSS and smoke tree sharpshooter also identified for the first time the sharpshooter X-wave, a waveform family that definitively represents xylem penetration by the stylets. The X-wave incorporates the B1w, B1s, other waveforms to be discussed, and a short C waveform event. X-ray images of GWSS feeding taken at the Argonne National Lab will also be discussed. Those findings support that the B1s and B1w of the X-wave represent egestion (expulsion) of fluids from the precibarium into xylem, and likely represent the instant that Xylella fastidiosa cells are inoculated.