Waveform library for sharpshooters (Hemiptera: Cicadellidae: Cicadellinae): Characterization of EPG waveforms at various input impedances

Blue-green sharpshooter, Graphocephala atropunctata Say, glassy-winged sharpshooter, Homalodisca vitripennis (Germar), and related cicadelline leafhoppers transmit Xylella fastidiosa (Xf), the causative agent of Pierce’s disease of grape.  Understanding transmission mechanisms of Xf depends on understanding the role of feeding behavior in transmission.  The primary means of studying sharpshooter feeding is electrical penetration graph (EPG) monitoring.  In the present studies, a four-channel, Backus and Bennett AC-DC monitor was used to characterize EPG waveforms produced by adults of G. atropunctata, as a model sharpshooter species.  Stylet probing of sharpshooters was recorded at input impedances ranging from 10⁶ to 10¹⁰ Ohms, plus 10¹³ Ohms, to develop a waveform library.  Waveforms previously correlated via microscopic examination of salivary sheaths were characterized for their electrical origins (R versus emf components) via switches among input impedances and applied signal types.  Electrical origins supported previously hypothesized biological meanings of sharpshooter waveforms.