Probing Behaviour of thrips. Behavioural study on the feeding of Western flower thrips related to Tomato spotted wilt virus transmission and host plant susceptibility

Western flower thrips, Frankliniella occidentalis , feeds in a piercing sucking manner and is a worldwide pest on many ornamental and vegetable crops. Thrips can feed on different parts of the plant; leaves, stems, flowers and fruits. On leaves thrips can ingest the cell contents of epidermal, mesophyll, and parenchymal cells, but their mouthparts cannot reach the vascular tissue. Western flower thrips can also transmit Tomato spotted wilt virus (TSWV) during probing. My research has shown that individual probes can be divided in several phases using an electrical monitoring system, electrical penetration graph (EPG) technique. Six different phases have been distinguished: P, Q, R, S, T, and U. These phases were shown to reflect different behavioural activities and are represented by different waveforms. Waveform P represents mandibular stylet insertion through the surface of the leaf, during waveform Q the maxillary stylets are inserted and salivation occurs and waveform R represents ingestion of the cell contents. Of waveform S and U it is only known that they reflect mandibular action, and during waveform T probably the stylets are retracted. Not all these waveforms occur in every individual probe and waveform transients are often gradual therefore I suggest for practical reasons to distinguish only phases for: the 'puncture phase, PQ', also including S, and the 'feeding phase, R', also including T and U. Transmission of TSWV occurs with salivation during waveform Q in the puncture phase. TSWV can be transmitted in a single probe without ingestion, but only in one of 125 probes transmission was found to be successful. Therefore, more probes made by a viruliferous thrips result in a higher chance of virus transmission. The probability of TSWV transmission is not the same in every probe; the duration of the salivation phase has a positive effect whereas the duration of the ingestion phase has a negative effect. Host plant resistance against TSVW works well in pepper, but combined with thrips resistance it can be more durable. This can be concluded because this study found that thrips resistance only results in small changes in the probing behaviour and these changes hardly influence TSWV transmission.