Acceptability of different species of Brassicaceae as hosts for the cabbage aphid

The probing and feeding behaviour of the cabbage aphid, Brevicoryne brassic ae (L.), (Homoptera, Aphididae) was studied on several plant species that r epresented various levels of acceptability: Sinapis alba L. (a permanent ho st plant), Capsella bursa-pastoris (L.) Med., Thlaspi arvense L., Lunaria a nnua L., Erysimum cheiranthoides L. (accidental host plants), Vicia faba L. (a non-host plant), using the electrical penetration graph technique (EPG) . B. brassicae on V. faba did not show any patterns related to penetration of phloem vessels. Stylet penetration was deterred on L. annua and E. cheir anthoides where non-penetration prevailed, the periods of sap ingestion wer e short or did not occur, the percentage of time spent in the phloem was co nsistently low (5-6%) and E1 salivation predominated. The pathway activitie s were not suppressed on C. bursa-pastoris and T. arvense and the aphids sp ent an average of 3 h in the phloem during the 8-h experiment. However, a c onsiderable delay between finding and accepting the phloem and a substantia l proportion of E1 salivation (20-30% of all phloem activities) indicated a deterrent factor in the sieve elements of these plants. Aphid probing and sap ingestion were rarely interrupted on S. alba. The results of this study suggest that the deterrent agents vary in activity and may hinder stylet p enetration at different levels (epidermis, parenchymatous tissues and/or ph loem elements), depending on the plant species.