Characterising the root-feeding habits of grape phylloxera using electrical penetration graph

Abstract

Feeding by the radicicolae form of grape phylloxera (Daktulosphaira vitifoliae) leads to gall development and root decay on Vitis vinifera and may cause economic damage for the vineyard. This damage is managed by planting V. vinifera grafted to resistant rootstocks. The processes of grape phylloxera feeding and the mechanisms of rootstock resistance can be investigated with the application of the Electrical Penetration Graph (EPG) technique. EPG technology has been applied to investigate the feeding behaviour of aphids for over 40 years, but has not previously been reported on grape phylloxera. Deterrents for the application of EPG technology to grape phylloxera included the relative small size of the insect, the root-feeding habit and a lack of correlation studies involving non-vascular feeding insects. Here we report that EPG has successfully been applied to study the feeding behaviour of radicicolae grape phylloxera. EPG recordings have been obtained from both excised root and tissue culture plant recording systems, and from first instar to adult life stages of the insect. Feeding patterns have been recorded for up to eight hours and a number of EPG waveforms have been identified. To determine signature-feeding waveforms, initial studies involved recording insects in an active feeding position. In order to establish an understanding of the complete feeding behaviour of grape phylloxera (including stylet penetration and pathway to ingestion), insects in the probe initiation position were disrupted from feeding and relocated onto a new food source. Disturbed insects successfully re-established feeding.