Electrical recording of plant penetration by western flower thrips

Plant penetration by western flower thrips (Frankliniella occidentalis (Pergande)) was analysed with the electrical penetration graph technique (EPG, DC-system). Thrips attached to a gold wire were included in an electrical circuit to record EPGs when penetrating the plant tissues with their stylets. Three basic EPG waveforms have been distinguished, correlated with stylet penetration into cells, salivation, and ingestion, respectively. The main difference with EPGs of Homoptera is the occurrence of continued separate penetrations that are not necessarily followed by ingestion. Insertion of the stylets causes strong voltage fluctuations in the EPG. We could confirm earlier evidence that penetration of cells and subsequent ingestion of (part of) the protoplast takes less than 20 seconds. Repeated short penetrations can be followed by a continuous feeding pattern during which the stylets are not withdrawn. The same sequence of waveforms is produced on other plant parts such as fruits or pollen grains. The specific waveforms are mainly caused by electromotive force (emf). The emf component was recorded with high resolution and the correlation of waveform details with activities of the cibarial muscle system is discussed.