|WALTER, ANDREW - University Of California, Davis
Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2017
Publication Date: 12/1/2017
Citation: Backus, E.A., Cervantes, F.A., Walter, A.M. 2017. An EPG waveform library for sharpshooters and preliminary effects of applied voltage on behaviors controlling Xylella fastidiosa inoculation. CDFA Pierce's Disease Control Program Research Symposium. p. 170.
Technical Abstract: Electropenetrography (EPG) waveforms represent electrical conductivity of fluids flowing through an insect’s mouthparts. Over the 50 years since its invention, EPG has undergone three major electronic transformations. The newest, third generation of electropenetrograph, the AC-DC EPG monitor, offers the researcher a selection of 12 settings so that recordings can be tailored to the characteristics of the study species. Different information about feeding can be revealed by each setting, with varying contributions from either of two electrical origins: biopotentials or electrical resistance. Thus, a researcher can develop a library of waveform appearances for each setting, to reveal the largest number of waveforms from a balance of electrical origins. Waveforms of the blue-green sharpshooter, Graphocephala atropuncata, were recorded using all 12 amplifier settings with varying applied voltages to develop the first, complete waveform library for any sharpshooter species. DC applied signals, especially at high applied voltages, apparently prevented the insects from initiating probing, until the signal was switched to AC or the insects were very hungry. Thus, further, quantitative testing of effects of AC and DC, low and high voltages was begun. The first of two, 2x2 factorial tests was completed. Eight G. atropunctata were recorded per treatment, exposed to AC signals at low voltage (50 mV) or high voltage (200 mV) at amplifier sensitivities of 107 or 109 Ohms; a future test will use the same experimental design but with DC signals. Waveforms from the AC experiment were statistically analyzed via mixed model ANOVA and LSD pairwise comparisons. Results showed that AC voltages are relatively benign, with few significant differences. The differences found were in the X wave, the biopotential-dominated waveform representing “spitting up” of mixed fluids from the mouth cavity. High voltage caused longer overall performance of X waves. Thus, experiments using EPG to study the Xf inoculation behavior should use low AC voltages. The best amplifier sensitivities to use for future EPG studies of G. atropunctata were 108 Ohms for host plant resistance studies emphasizing pathway waveforms, or 109 Ohms for transmission studies emphasizing the X wave.