Electrical penetration graphs from Cicadulina mbila on maize, the fine structure of its stylet pathways and consequences for the transmission efficiency of geminiviruses

The efficiency with which a plant virus is transmitted by its vector(s) depends from its feeding behavior on plants. Using a DC based system, an electrical penetration graph analysis was carried out on maize with die leafhopper Cicadulina mbila Naudé (Homaptera: Cicadellidae), vector of Maize streak virus (Mastrevirus, Geminiviridae). Five distinct electrical penetration graph waveforms were distinguished by temporal and spectral features as well as by statistical analysis of their median voltage and duration. By changing the polarity of the system voltage and the level of the input resistor it was shown that the waveforms are mainly determined by electromotive forces (emf). Based on the correlation between waveforms and the fine structure of the stylet pathways using transmission electron microscopy, the insect's activities have been associated with five waveforms: stylet pathway (waveform 1), active ingestion (waveform 2), stylet work (waveform 3), salivation (waveform 4) and passive ingestion (waveform 5). Like waveform El and E2 of aphids, waveforms 4 and 5 of C. mbila correspond to feeding activities in sieve tubes. However, unlike aphids which probe briefly in non-vascular cells, waveform 2 corresponds to active ingestion in these cells, of which their cell content is partially ingested and their organelles integrity severely affected. These observations suggest that this specific feeding feature, typical of leafhoppers, determines their ability to acquire geminivirus virions located in the plant cell nucleus. This specific feeding behavior was compared to that of whiteflies of the genus Bemisia, vector of the geminiviruses of the genus Begomovirus, for which such a vigorous probing was not described. (Texte intégral