Effects of experimental stress factors on probing behaviour by aphids

Probing behaviour of Aphis fabae Scopoli and Rhopalosiphum padi (L.) was te sted in different stress situations normally occurring in aphid-plant studi es such as interruption of feeding or starvation, transfer to a new plant, and attachment to the electrode wire. The DC electrical penetration graph ( EPG) technique and a 'honeydew clock' were used to collect data on behaviou ral effects of these stress conditions. As a general effect, an interruptio n of feeding behaviour acted as a 'reset', i.e., the same sequence and time course of probing events were shown, irrespective the interruptions durati on, from 1-100 min. Nevertheless, some minor differences were found, especi ally in A. fabae. Increased interruption times (deprivation from the host p lant) stimulated the aphids to insert their stylets earlier. When A. fabae was put back on its host plant after a one min interruption phloem feeding started earlier than with longer interruption times, but only when it was p ut back to the same plant and feeding site on which it fed before. It is co ncluded that this effect is at least partly due to 'memory' of previous pro bing/feeding experience on the plant as it vanishes with longer interruptio n times. This explanation also holds for phloem salivation (E1) before star ting sustained sap ingestion, which was reduced on the previous feeding sit e, but only after the one min interruption in A. fabae. The aphid-plant spe cificity appeared high in these effects. Both aphids were somewhat affected by wiring, resulting in earlier probing, longer total pathway phase, and l ess and later phloem feeding (as reflected by honeydew excretion). Thus con firming, that the evaluation of EPG results can be improved with supplement ary data from free aphids.