The stylet penetration activities of Peregrinus maidis (Ashmead) (Homoptera: Delphacidae), vector of Maize mosaic virus (MMV) and Maize stripe virus (MStV) were studied by electrical penetration graphs (DC-EPG) on resistant and susceptible maize inbred lines. Multivariate analyses were applied to two sets of data obtained by manual and automated methods of waveform recognition from digital EPG recordings. For both methods, the variables, which mostly explained the resistance-susceptibility status of the maize lines, appeared to be related to the passive ingestion in phloem vessel and stylet pathway and to a lesser extent to active ingestion in xylem and to non-penetration. In spite of a great variability within each plant genotype, plants could be divided in three classes, susceptible, slightly resistant and resistant to the virus transmission. These results are discussed in relation to the possible mechanism of maize resistance to P. maidis and the usefulness of automated waveform recognition with the software "EPG soft" for plant breeding.