Electrical Penetration Graph

A Electrical penetration graph also briefly EPG technique is a method of investigation in biology. It is used to investigate the absorption behavior of an aphid (or other insects with piercing -sucking mouthparts ).

To an electric circuit is created between the insect and the plant, by using an electrode in the bottom of the potted plant, a fine gold wire by means of electrically conductive adhesive attaching a very thin connecting the insect. This circuit contains an electrical resistor ( R ) a voltage source ( V). Once the stilets the aphid penetrate the plant, the circuit is closed, and you get an AC voltage (EPG ) signal, which is amplified and recorded. By an AD converter board, this signal is digitized at a converter frequency of about 100 Hz and may be recorded on the computer.

The voltage change form different characteristic patterns, referred to as waveforms. The different main patterns that are distinguishable for aphids have been characterized in their exchange relationships with their penetration behavior and the position of the piercing bristle tip in the plant tissue. The electrical origin of the signal is caused simultaneously by two different sources:

These two signal components, the voltage which drops at the resistor (R) and the source voltage generated by the combination of plant insect superimposed at the measurement point.

The R- components are mainly due to the movements of the lancets. The emf components, however, are caused by the " membrane potentials " of the plant cells - when they are pierced by the piercing bristles - as well as streaming potentials due to the flow movements of fluids (cell juice, saliva) in the fine piercing bristle channels. Muscle and neural potentials in the insect are outside of the circuit, and thus do not seem to contribute to the EPG signal. Both inventory Split, "R" and " emf ", contain important biological information on the activities of the insect and the positions of the piercing bristle tips in the plant tissue.

The measuring system, which was introduced by McLean and used in the Kinsey (1964 ) AC as power source (AC ) based on a modulation of the voltage, the extent caused by the changes in resistance in the insect, similar to the signal transmission in the AM radio. With this AC system, the emf components in the signal could not be detected. Later, the power source of direct current ( DC) has been replaced, and two DC system versions have been developed.

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

Currently, there are actually 3 EPG systems:

The EPG of the regular DC system contains the widest portion of biological information in the signal, therefore, is more complex than the signals of the emf - or R- amplifier, but provides the most extensive and most relevant biological information.