Lobesia botrana (Lepidoptera: Tortricidae) larval population assessment by damage to grape flowers: could empty larval nests monitoring be useful?

Abstract: A correct accurate determination of the population size is the basis of successful pest management procedures and is of primary importance in the protection against the European grapevine moth (EGVM, Lobesia botrana). During three consecutive years, we quantified the time course of larval damage to grape flower buds and the presence of the different larval instars of EGVM in an experimental vineyard (INRA Bordeaux Aquitaine research center). From a total of 1003 so called larval damage (glomerula), 704 living larvae were obtained. We determined the larval instars of all samples. There was a significant correlation between damage per larva and larval population densities. Intra-specific competition between larvae and avoidance of larval parasitism are the most probable causes of empty glomerulae, and of the relation we observed. We assume that grape damage could efficiently be quantified also by estimating the number of empty glomerulae as a good indicator of larval density.