Feeding behaviour of the aphid Rhopalosiphum padi (Hemiptera : Aphididae) on nitrogen and water-stressed barley (Hordeum vulgare) seedlings

Electrical penetration graphs (EPGs) were used to examine the probing behav iour of adult apterous Rhopalosiphum padi (Linnaeus) on barley seedlings gr own under conditions of nitrogen or water stress. Aphids took significantly longer to reach and ingest from sieve elements of nitrogen-deficient seedl ings than from nitrogen-sufficient seedlings but there were no such differe nces between water-stressed or well-watered seedlings. On both nitrogen and water-stressed seedlings the average length of each individual period of s alivation into the sieve element was significantly greater compared with th eir respective unstressed controls.