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

1 Bunch- zone leaf removal reduced infestation by Lobesia botrana, although the mechanism responsible for this effect is unknown. 2 Based on themortality of eggs and newly- hatched larvae exposed to high temperatures (= 37 degrees 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. 3 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 degrees C or more above air temperature, and the highest mean temperatures occurred on southwest- side bunches followed by west- and south- side bunches. 4 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. 5 The hypothesis that the high temperatures reached by sun- exposed berries cause egg and especially larval mortality is confirmed. 6 Bunch- zone leaf removal combined with optimized grapevine- row orientations can improve L. botrana control.