Characterisation of the feeding behaviour of western flower thrips in terms of electrical penetration graph (EPG) waveforms

Western flower thrips, Frankliniella occidentalis (Pergande) causes damage to plants when they are feeding. Also, this thrips species transmits Tomato spotted wilt virus (TSWV) during stylet penetration. We investigated the penetration behaviour (probing) of thrips on pepper leaves and on liquid diet by electrical penetration graph (EPG, DC-system) recording. In addition, we used high-magnification video observations to correlate EPG waveforms with the insect's posture, head movements, and muscle contractions. Also, EPGs were correlated with probing on liquid diets containing radio-active tracers to distinguish and quantify ingestion waveforms. The previously described waveforms P, Q, and R were distinguished and additionally, a new waveform 'S' was distinguished. Waveform P could be linked with mandibular leaf penetration, waveform Q presumably with insertion of the maxillary stylets, and waveform R with ingestion of cell contents, whereas waveform S could not be correlated with any behavioural activity. Histology of the feeding damage in pepper leaves shows that thrips ingests the contents of multiple cells per probe.