Biological performance of the grape berry moth on red and white vine cultivars

The grape berry moth (GBM), Endopiza viteana (Lepidoptera: Tortricidae), is a specialist herbivore that is a major pest of vineyards of eastern United States and Canada. While feeding on berries GBM, larvae ingest carbohydrates and tannins (phenolic acid), whose main function is to defend plants, notably from leaf-eating insects. We studied the biological performance of GBM by adding various concentrations of glucose and tannic acid into diets made of grapes belonging to two red (Marechal Foch, Seyval noir) and two white (Vidal and Seyval blanc) vine cultivars. The biological parameters measured were pupal weight, larval developmental time and survival of GBM. Given the known effects of glucose and tannins in leaf-eating lepidopterans, we expected that: 1) GBM larvae would have a better biological performance when developing on white grape diets than on red grape diets; 2) sugars added to white grape diets would stimulate larval growth and increase pupal weight more than red grape diets: 3) tannins added to white grape diets would increase developmental time and decrease pupal weight, but less than with red grape diets. Our results differed from the expectations. Larvae performed best on red grape diets, which contained higher tannin concentrations. Adding glucose to the diets had no positive effect on biological performance of GBM larvae. Males and females GBM reacted differently to additions of tannic acid. Our results challenge some aspects of current theories on the effects of nutritional quality.