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Electrical penetration graph (EPG)

The electrical penetration graph or EPG is a system used to study the interaction of insects with plants. It can be used to study the way in which insects can find and feed from the phloem of the plant. It is a simple system consisting of a partial circuit which is only completed when a species such as aphids, which are the most abundantly studied, inserts its stylet into the plant in order to probe the plant as a suitable host for feeding. The completed circuit is displayed visually as a graph with different waveforms indicating either different insect activities such as saliva excretion or the ingestion of cellular contents or indicating which tissue type has been penetrated (i.e. phloem, xylem or mesophyll). (adapted from Wikipedia)


Asian citrus psyllid adult and nymph feeding

This Electrical penetration graph (EPG) study compared D. citri nymphs and adults feeding on healthy and infected citrus plants to study CLas acquisition.

EPG recordings over 42 hours were performed to compare the feeding behavior of D. citri adults and 4th or 5th instar nymphs feeding on CLas-infected or healthy citron plants. Nymphs performed more individual bouts of phloem ingestion (E2) and recorded longer phloem ingestion total time compared with adults, whereas adults performed more bouts of xylem ingestion (G) and recorded greater total time of xylem ingestion compared with nymphs. Quantitative polymerase chain reaction tests indicated that 58% of nymphs and 6% of adults acquired CLas during the 42 hours EPG-recorded feeding on infected plants. In a histological study, a greater proportion of salivary sheaths produced by nymphs were branched compared to those of the adults. Our results strongly suggest that more bouts and longer feeding time in the phloem by nymphs may explain their more efficient CLas acquisition from infected plants compared to adults. This is the first EPG study comparing nymphs and adults of D. citri on healthy and infected citrus plants in relation to CLas acquisition.


Examples of electrical penetration graph recordings from George et al. 2018 showing feeding activities of Diaphorina citri adults (A) and nymphs (B) during 42 hour recordings. Vertical dashed lines with double arrows indicate periods of continuous phloem ingestion (waveform E2)


Citrus variety used: Citron
Insects: Asian citrus psyllid nymphs (early fifth instar) and adults (8-10 days old)
Treatments:
  1. Nymph feeding on healthy citron (18 reps)-CN
  2. Nymph feeding on infected citron (33 reps)-IN
  3. Adult feeding on healthy citron (18 reps)- CA
  4. Adult feeding on infected citron (33 reps)-IA
Each EPG recording is for continuous 42 hours under complete lighted (fluorescent) conditions.
The linked data contains
  1. Actual recordings-8 (channels) recordings in each run
  2. Human annotated files (File name by the treatment, channel in each run and date of recording)
  3. Excel sheets summarizing the data


Citation: Justin George, El-Desouky Ammar, David G. Hall, Robert G. Shatters Jr. and Stephen L. Lapointe (2018): Prolonged phloem ingestion by Diaphorina citri nymphs compared to adults is correlated with increased acquisition of citrus greening pathogen Scientific Reports 8: 10352