Comparison of bioassays to biotype grape phylloxera (Daktulosphaira vitifoliae Fitch) on Vitis ssp.

Grape phylloxera biotypes exist throughout viti- cultural regions causing substantial economic losses. In the past different biotyping assays were employed to determine host adaption and potential harm of phylloxera strains or field populations. Standardised and efficient laboratory assays are required to define biotypes according to their aggressivity as well as to make accurate pest management and quarantine decisions. We aim to provide information on the consistency of the three most commonly used assays to accurately identify grape phylloxera biotype. Two phylloxera biotypes (A, C) were tested on two host plants (rootstock 'Teleki 5C' V. berlandieri x V. riparia and V. vinifera 'Riesling') using three assays: Simple isolation chamber, excised root bioassay and aseptic dual culture bioassay. Insect number, life table and plant-based response parameters (root galling) were compared. The simple isolation chamber and aseptic dual culture bioassay produced consistent results, whereas the excised root bioassay did not. We demonstrated that biotype results depend on whether the technique used is tuberosity- or nodosity-based. Pest management decision based on a single assay may inaccurately assess the phylloxera aggressivity potential. Thus, we recommend using two assay types which allows comparison of both root gall types.