Author
DUGRAVOT, SEBASTIEN - UNIVERSITY OF RENNES | |
Backus, Elaine | |
REARDON, BRENDON - UNIV OF CA, RIVERSIDE | |
MILLER, THOMAS - UNIV OF CA, RIVERSIDE |
Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/7/2008 Publication Date: 12/2/2008 Citation: Dugravot, S., Backus, E.A., Reardon, B.J., Miller, T.A. 2008. Correlations of cibarial muscle activities of Homalodisca spp. sharpshooters (Hemiptera: Cicadellidae) with EPG waveforms and excretion. Journal of Insect Physiology. 54:1467-1478. Interpretive Summary: Fluid flow in and out of the stylets of piercing-sucking insects called sharpshooters is crucial for transmission of Xylella fastidiosa, the causal agent of Pierce’s Disease. Herein we describe the contractions of muscles that power the cibarial pump and precibarial valve, by electrically recording signals from their muscles and video-recording the movements of the lid of the cibarial pump. We also correlate those movements with electrical penetration graph (EPG) waveforms representing feeding, and with production of droplets of urine. One of the EPG waveforms, B1s, represents fluid flow caused by precibarial valve muscle contractions. Another EPG waveform, C, represents fluid flow propelled by cibarial muscle contraction, i.e. active ingestion. Moreover, the fine structure of the C waveform represents directionality of fluid flow. Rhythmic bouts of cibarial pumping were strongly correlated with sustained production of urine droplets. These findings will allow researchers to use EPG waveforms to identify the instant when X. fastidiosa bacteria enter or exit the stylets, thus establishing the mechanisms of acquisition and inoculation, and allowing use of EPG to identify host plants that will resist bacterial inoculation. Technical Abstract: Fluid flow in and out of the stylets of xylem-ingesting sharpshooters (Hemiptera: Cicadellidae: Cicadellinae) is crucial for transmission of Xylella fastidiosa, the Pierce’s Disease bacterium, yet has been inadequately studied. Herein we describe research on the contractions of muscles that power the cibarial pump and precibarial valve, by electromyographically (EMG) recording their muscle potentials and video-recording the movements of the cibarial diaphragm. We also correlate those movements with electrical penetration graph (EPG) waveforms representing feeding, and with excretory droplet production. Results showed that the B1s waveform represents fluid flow caused by precibarial valve muscle contractions, i.e. valve fluttering that propels fluid back and forth across the precibarial chemosensilla. The C waveform represents fluid flow propelled by cibarial muscle contraction, i.e. active ingestion. There is a 1:1 correspondence of each cibarial pump to each C waveform episode. Moreover, the valley portion of each C episode represents muscular diaphragm uplift, therefore the suction that pulls fluid into the stylets. The plateau portion represents release of the diaphragm, propelling fluid into the esophagus or out of the stylets. Thus, fine structure of the EPG ingestion waveform represents directionality of fluid flow, supporting the role of streaming potentials as the electrical origin of that waveform. Rhythmic bouts of cibarial pumping were strongly correlated with sustained production of excretory droplets. However, neither the onset nor cessation of ingestion was correlated with onset or cessation of excretion, respectively. Implications for using EPG to understand the mechanism of X. fastidiosa transmission are discussed. |