Salivation into sieve elements in relation to plant chemistry: the case ofthe aphid Sitobion fragariae and the wheat, Triticum aestivum

Extended sieve element salivation (E1 waveform in the electrical penetratio n graph) is a characteristic activity during early sieve element punctures, particularly in resistant plants. In order to explore a chemically-mediate d mechanism of resistance associated with sieve element salivation, we comp ared the pattern of feeding behaviour of the aphid, Sitobion fragariae (Wal ker), on two cultivars of the wheat Triticum aestivum L., with different co ncentrations of hydroxamic acids (Hx). During 24 h of electronic monitoring , aphids dedicated over 50% of the total time to phloem ingestion from the sieve elements. Total time allocated to E1 in the experiment, time to first E1 within the experiment, time allocated to E1 before a sustained phloem i ngestion (E2) and the contribution of sieve element salivation to the phloe m phase (E1/[E1+E2]) were significantly higher in the high-Hx cultivar. The increased salivation in plants with higher contents of Hx suggests the exi stence, at least in this system, of a chemically-mediated sieve element con straint.