Correlations of cibarial and precibarial muscle activities with EPG waveforms and excretion in sharpshooter (Hemiptera: Cicadellidae: Cicadellinae) vectors of Xylella fastidiosa

• Author(s): Backus, Elaine; Dugravot, Sebastien; Miller, Thomas; Reardon, Brendon;
• Abstract: Fluid flow in and out of the stylets of xylem-ingesting sharpshooters (Hemiptera: Cicadellidae: Cicadellinae) is powered by muscles of the cibarial pump. Such fluid flow is crucial for transmission of Xylella fastidiosa, the Pierces Disease bacterium, yet has not been rigorously studied via electrical penetration graph (EPG) technology. By electromyographically (EMG) recording cibarial muscle potentials and video-recording movements of the cibarial diaphragm, we correlated those movements with waveforms representing ingestion and excretory droplet production. Results definitively showed that the C waveform represents fluid flow propelled by cibarial muscle contraction, i.e. active ingestion. There is a 1:1 correspondence of each cycle of cibarial muscle contraction/relaxation to each plateau of EPG waveform C. Moreover, the rise portion of each C plateau represents muscular diaphragm uplift, therefore the suction that pulls fluid into the stylets. The top of the plateau represents holding then release of the diaphragm, propelling fluid into the esophagus or the precibarium. 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.
• Publication Date: Jan 2007
• Journal: Journal Of Insect Physiology