Electrical penetration graphs of thrips revised: Combining DC- and AC-EPG signals

Within thrips feeding behaviour, sequences of four waveforms have been distinguished earlier in the DC-EPG, i.e. P, Q, R and S, representing mandibular stylet insertion, maxillary stylet insertion, ingestion, and repetitive mandibular insertion, respectively. During signal analysis it appeared that transitions from one waveform to the next were difficult to establish, making results ambiguous. In order to improve the quantitative reliability of the thrips' EPG data, the DC-EPGs were recorded concurrently with AC-EPG signals, thus providing two signals from the same activities containing different information. The additional AC information did not solve most quantification problems, however. We now propose to merge waveforms P, Q, and S, into 'puncture phase' (indicated by PQ) and waveforms R, T, and U, into 'feeding phase' (indicated by R), rather than trying to analyse all separate waveforms. This will provide a more reliable and much less laborious analysis of thrips probing behaviour. Waveforms T and U are two novel waveforms identified here by combining DC- and AC-EPG recordings with concurrent video recordings. Waveform T represents a single mandibular thrust embedded in waveform R and waveform U represents the end of a probe, presumably the retraction of the maxillary stylets.