Transmission of non-persistent plant viruses is related to aphid behaviour during superficial brief probes. A widely accepted hypothesis postulates that virus acquisition occurs during ingestion of plant cell contents, and inoculation during egestion or regurgitation of previously ingested sap. Although conceptually attractive, this ingestionegestion hypothesis has not been clearly demonstrated. Furthermore, it overlooks the anatomy of the tips of the stylets (mouthparts) and, consequently, the potential role of salivation in the inoculation process. Here, we used the electrical penetration graph (EPG) technique to investigate aphid-stylet activities associated with uptake (acquisition) and release (inoculation) of two nonpersistently transmitted viruses. Our results show that acquisition occurs primarily during the last sub-phase (II-3) of intracellular stylet punctures, whereas inoculation is achieved during the first sub-phase (II-1). An alternative mechanism to the ingestion-egestion hypothesis is proposed on the basis of our findings.The transmission of non-persistent plant viruses is unique to aphids (Homoptera : Aphididae) because they exhibit specific and characteristic activities during brief (a few seconds or minutes) and superficial probes, involved in host plant recognition (Pollard, 1973). Two different hypotheses have been proposed to explain the mechanism of transmission. The first, so-called stylet-borne hypothesis (Kennedy et al., 1962),

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