PLANT PENETRATION BY PEA APHIDS (ACYRTHOSIPHON-PISUM) OF DIFFERENT PLANT RANGE

Plant penetration by the stylets of six clones of the pea aphid, Acyrt hosiphon pisum, on Vicia faba (acceptable to all clones) and Pisum sat ivum (acceptable to 3/6 clones) was investigated by the DC electrical penetration graph technique. In a 10 h recording period, 93% of 144 ap hids exhibited sustained feeding on phloem sap. Significant interclona l differences were observed for the incidence of potential drops (indi cative of brief punctures of plant cells) and the duration of waveform E1 (insect salivation into a sieve element). In addition, the total d uration of the sieve element phase and the duration of completed 'bout s' of sustained feeding differed between the two test plants, in a fas hion varying between clones. However, these differences could not be r elated to the acceptability of plants to the different aphid clones. T he duration of the stylet pathway phase preceding the first sustained feeding on phloem sap did not vary significantly with either aphid clo ne or plant. It is concluded that the resistance of Ft sativum to cert ain A. pisum clones does not arise from factors impeding either stylet penetration through the plant tissues or the maintenance of feeding f rom the sieve elements. It is proposed that host plant affiliation of A. pisum may be mediated primarily by specific olfactory or gustatory cues, before the aphid initiates stylet penetration of the plant.