Probing behaviour of the green peach aphid Myzus persicae on resistant Prunus genotypes

Electrical penetration graphs of Myzus persicae (Sulzer) (Homoptera: Aphidi dae) feeding behaviour on four resistant and two susceptible genotypes of p each (Prunus persica L. Batsch) and related species showed that resistance was mainly linked to (i) reduced duration of phloem sap uptake, (ii) reduce d percentage of pattern El (salivary secretion into sieve elements) followe d by pattern E2 (sap ingestion) and (iii) increased number of shifts from E l to E2 and back, These results suggest the unsuitability of phloem sap, an d thus repetitive failures to initiate sustained ingestion. Extensive compa risons of the EPGs also revealed more specific trends. Aphids on the most s usceptible cultivar GF305 produced significantly longer potential drops tha n on other peach genotypes. On the resistant Rubira, aphids generated more penetrations before the first E occurred, indicating the possible presence of a resistance factor before the phloem was reached. The clone P1908 of th e wild species Prunus davidiana displayed traits of both susceptibility (le ss but longer probes) and resistance. In particular, aphids produced more E l, suggesting difficulties in preparing sieve elements before feeding. The aphid probing process could be correlated with aphid settling behaviour and bionomics, as previously reported, and gave evidence for the existence of different mechanisms underlying resistance in the tested genotypes against M. persicae.