Grape phylloxera, Daktulosphaira vitifoliae (Fitch) (Hom., Phylloxeridae), population response to preformed tuberosities

Abstract

AbstractLaboratory tests were used to assess feeding and population growth of three grape phylloxera strains on preformed root tuberosities of the grape rootstock ‘AXR#1’. The tuberosities were formed on root sections by grape phylloxera biotypes A or B (first generation), after which the insects were removed and the roots were reinfested with a second cohort (second generation). Second generation phylloxera were of biotypes A or B, or a third strain, ‘SG’. Preformed tuberosities were preferentially colonized over non‐tuberosity portions of roots by all phylloxera irrespective of whether the first generation was biotype A or B. All three phylloxera types had a shorter time to maturity and a higher percentage reaching maturity when they fed on tuberosities preformed by biotype B rather than by biotype A; there was no difference in fecundities. Phylloxera also established, grew and reproduced on non‐tuberosity portions of the roots with preformed tuberosities. The time to maturity on the non‐tuberosity portions of the roots was longer and the fecundity was lower than on the preformed tuberosity portions of the same roots. After 45 days on AXR#1 roots previously infested by biotype A phylloxera, biotype A, B, and strain SG populations increased 11‐, 29‐ and 9‐fold, respectively. On roots previously infested by biotype B, the increases were 59‐, 107‐ and 44‐fold, respectively. Formation of tuberosities by phylloxera on AXR#1 increased the vulnerability of the root to subsequent attack at the preformed tuberosities, but not at other portions of the roots. Implications of these findings to population dynamics and bioassays for screening for phylloxera resistance in candidate rootstocks are discussed.