Grape phylloxera (Homoptera: Phylloxeridae) temperature threshold for establishment of feeding sites and degree-day calculations

Abstract

In laboratory bioassays with grape, Vitis vinifera L., roots, grape phylloxera, Daktulosphaira vitifoliae (Fitch), did not develop egg hatch when held at a constant 18°C. However, a 2-d exposure to 24°C during the 1st instar prompted some insects to develop. On preformed feeling sites, phylloxera were able to develop at 18°C without any exposure to 24°C. These data suggest that the theshold temperature for establishment of a feeding site is > 18°C, and that the temperature threshold for maintenance of the feeding site, nutrient extraction and development is < 18°C. Calculations of degree-days necessary for development from egg batch to the adult stage in temperature regimes that are not constant give values different from calculations from bioassays data collected at constant temperatures. Therefore, current threshold and degree-day data for grape phylloxer are insufficient for predicting population growth in the field where temperature vary.