Electrical penetration graph

from Wikipedia, the free encyclopedia
Schematic representation of the EPG method

An electrical penetration graph , also known as EPG technology for short, is an examination method in biology. It is used to study the sucking behavior of an aphid (or other insects with stinging-sucking mouthparts).

To do this, the insect and the plant are electrically connected to an amplifier. The electrode for the insect consists of a fine gold wire (<20 µm) which is attached to the insect with an electrically conductive adhesive. A copper wire is used as the second electrode, which is simply inserted into the bottom of the potted plant. This circuit also contains an electrical resistor (R i ) and a voltage source (V). As soon as the aphid's stinging bristles penetrate the plant, the circuit is closed and a voltage signal ( EPG signal ) is obtained, which is amplified and recorded. This signal is digitized by an AD converter card at a converter frequency of around 100 Hz and can be recorded on the computer.

The voltage changes form different characteristic patterns, also known as waveforms , depending on the pricking activity of the aphid and the position of the piercing bristle tips in the plant tissue . The resulting signal patterns are caused by two different sources:

  1. due to the changing electrical resistance of the aphid or the stinging bristles in the plant (R components) and
  2. through electrical potentials that exist in the plant tissue and are derived via the piercing bristles ("electromotive forces" - emf component)

The R components are mainly created by the movements of the piercing bristles. The emf components, on the other hand, arise from the "membrane potentials" of the plant cells - when they are pierced by the piercing bristles - and as streaming potentials as a result of the flow movements of the liquids (cell sap, saliva) in the fine piercing bristle channels. Muscle and neural potentials in the insect are outside the circuit and thus do not seem to contribute to the EPG signal. Both components, "R" and "emf", contain important biological information about the activities of the insect and the positions of the bristle tips in the plant tissue.

The measuring system introduced by McLean and in which Kinsey (1964) used alternating voltage as the voltage source, was based on a modulation of the voltage, the magnitude of which was caused by the changes in resistance in the insect, similar to the signal transmission in an amplitude modulation . With this alternating current system, the emf components in the signal could not be detected. The voltage source was later replaced by DC voltage , and two DC system variants were developed.

In a system, the input resistance (R i ) is very high (greater than 1 GΩ ) so that changes in resistance of the insect are insignificant and only the emf components are registered. The regular DC system has an input resistance that has roughly the same value as the average electrical resistance of the aphid-plant combination, and thus enables optimally to determine the ratio of the resistance and the emf components to the same extent.

There are actually three EPG systems currently in existence:

  1. the "regular" DC system, which registers both signal components and is the most widely used,
  2. the 'emf amplifier', a DC system that only records the emf components and
  3. the 'R amplifier', the AC system that only records the R components.

The EPG of the regular DC system contains the broadest amount of biological information in the signal and is consequently more complex than the signals from the emf or R amplifier, but gives the most extensive and relevant biological information. According to the amplifier setting, the signal should have a positive voltage. A distinction is made between three signal levels, the extracellular signals with a clearly positive voltage (<5 V), the intracellular signals (pd and E), with a significantly lower voltage, and the non-piercing phases on the 0 volt level.

The following main patterns are known for aphids:

extracellular signals:

  1. C = referred to as "pathway", it characterizes the puncture and propulsion of the piercing bristles between the cells within the cell walls . The two patterns "A", which were previously shown separately, signaling the puncture of the piercing bristles through the cuticle , and "B", which is created by the formation of the initial salivary sheath, are integrated into the C pattern .
  2. G = xylem sucking, a very regular pattern (<10 Hz) with a uniform amplitude , caused by "drinking water" after the piercing bristles have pierced the xylem
  3. F = stinging bristle problems. An even pattern with a higher frequency (> 10 Hz) that is associated with the coordination of the stinging bristle movement. It is assumed that in such cases the coordinated movement of the prickly bristle bundle is disturbed.

intracellular signals:

  1. pd = "potential drop" is a noticeable, brief (approx. 6-8 sec) drop in voltage within the C pattern. It is created by the penetration of the piercing bristles into a cell, whereby the derived membrane potential causes the voltage drop. The “pd” are divided into 3 phases (“pd-I” to “pd_III”), whereby various sub-phase patterns can be identified within the 2nd phase, which are associated with saliva release or cell sap uptake.
  2. E = Phloem contact of the piercing bristles, starting with the voltage drop typical for pd, following a regular pattern with positive voltage peaks = E1 , caused by the active injection of saliva into the phloem . As a rule, the E1 pattern changes into the E2 pattern, which is characterized by negative voltage peaks with a low amplitude. This E2 pattern is created during “sucking”, when the aphid ingests the phloem sap under overpressure. For this pattern u. a. responsible for opening and closing the pharyngeal valves at the transition to the esophagus .

Individual evidence

  1. ↑ Tjallingii, WF 1978. Electronic recording of penetration behavior by aphids . Entomologia Experimentalis et Applicata 24: 721-730

literature

  • McLean, DL, and MG Kinsey. 1964. A technique for electronically recording aphid feeding and salivation. Nature 202: 1358-1359.
  • Schliephake, E. et al. 2013. Barley yellow dwarf virus transmission and feeding behavior of Rhopalosiphum padi on Hordeum bulbosum clones. Entomologia Experimentalis et Applicata, 146 (3), 347-356
  • Philippi, J. et al. 2015. Feeding behavior of aphids on narrow ‐ leafed lupine ( Lupinus angustifolius ) genotypes varying in the content of quinolizidine alkaloids. Entomologia Experimentalis et Applicata, 156 (1), 37-51

Further information

  • EPG page from Dr. F. Tjallingii [1]