Effects of grapevine bunch exposure to sunlight on berry surface temperature and Lobesia botrana (Lepidoptera: Tortricidae) egg laying, hatching and larval settlement

Abstract

Bunch-zone leaf removal reduced infestation by Lobesia botrana, although the mechanism responsible for this effect is unknown. Based on the mortality of eggs and newly-hatched larvae exposed to high temperatures (≥37 °C) in the laboratory, the present study aimed to assess the influence of (i) bunch-zone leaf removal and grapevine-row orientation on berry surface temperature and (ii) bunch exposure to sunlight on egg and larval mortality. Berry temperatures were measured using a noncontact infrared thermometer in two vineyards and showed that, in direct sunlight, the temperatures of berry surfaces were 9 °C or more above air temperature, and the highest mean temperatures occurred on southwest-side bunches followed by west- and south-side bunches. The results of four two-choice field assays, carried out confining fertile females in cages with two bunches, one exposed and one non-exposed to sunlight, showed that: (i) the females did not avoid laying eggs on sun-exposed bunches and (ii) the lowest percentages of both egg-hatching and larval settlement occurred on sun-exposed bunches. The hypothesis that the high temperatures reached by sun-exposed berries cause egg and especially larval mortality is confirmed. Bunch-zone leaf removal combined with optimized grapevine-row orientations can improve L. botrana control.