EPG waveform library for Graphocephala atropunctata (Hemiptera: Cicadellidae): Effect of adhesive, input resistor, and voltage levels on waveform appearance and probing behaviors

Authors: Cervantes, Felix; Backus, Elaine; PERRING, THOMAS - University Of California

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2018
Publication Date: 6/7/2018
Citation: Cervantes, F.A., Backus, E.A., Perring, T.M. 2018. EPG waveform library for Graphocephala atropunctata (Hemiptera: Cicadellidae): Effect of adhesive, input resistor, and voltage levels on waveform appearance and probing behaviors. Journal of Insect Physiology. 109:21-40. https://doi.org/10.1016/j.jinsphys.2018.05.008.
DOI: https://doi.org/10.1016/j.jinsphys.2018.05.008

Interpretive Summary: Blue-green sharpshooter (BGSS) is a native pest of grapevines in California. This insect transmits the bacterium that causes Pierce’s disease of grapevines, severely affecting production. Development of blue-green sharpshooter- and Pierce’s disease-resistant varieties of grape depends in part upon better understanding of the means by which the insect feeds on the plant and the feeding mechanisms involved in transmission of the plant pathogen. Electropenetrography (EPG), one of the most useful techniques to study insect feeding behavior, has been used with BGSS in the past. However, the technology used in previous studies had limitations and was not standardized, making it difficult to compare results from different studies. Using the most current electropentrograph available (the AC-DC instrument), an updated waveform library was created that standardizes the methodology. Results strongly support that the instrument settings and type of adhesive can influence appearance of waveforms and quality of EPG information for BGSS. These findings will improve the use of EPG for BGSS to better support studies of host plant resistance, which will aid ultimately in development of BGSS- and Pierce’s disease-resistant grape varieties.

Technical Abstract: Graphocephala atropunctata is a vector of Xylella fastidiosa (Xf), the causal agent of Pierce’s disease of grapevines. A 3rd-generation, AC-DC electropenetrograph (EPG) was used to record stylet probing and ingestion behaviors of adult G. atropunctata on healthy grapevines. This study presents a complete, updated waveform library for this species, as well as effects of different EPG electropenetrograph settings and adhesives on waveform appearances. Both AC and DC applied signals were used with input resistor (Ri) levels (amplifier sensitivities) of 10^6, 10^7, 10^8 and 10^9 Ohms, as well as two type of adhesives, silver paint and silver glue. Description, characterization of electrical origins (R versus emf components) of waveforms, and proposed biological meanings are reported, as well as qualitative differences observed with different electropenetrograph settings and adhesives. A quantitative study with AC signal, using two applied voltage levels and two Ri levels also was performed. Intermediate Ri levels 10^7 and 10^8 Ohms provided EPG waveforms with the greatest amount of information, because both levels captured similar proportions of R and emf components. Similarly, use of a gold wire loop plus silver glue provided more definition of waveforms than a gold wire loop plus silver paint. In the quantitative study, the sharpshooter X wave was the most affected by changes in Ri and AC voltage level. Because the X wave probably represents X. fastidiosa inoculation behavior, an intermediate Ri level such as 10^8 Ohms with low voltage, AC applied signal, and gold wire loop plus silver glue are recommended to conduct future EPG studies of sharpshooter inoculation behaviors.