First reports of European Grapevine Moth (Lobesia botrana) in California began in Napa County vineyards in September 2009. In May and June, first-generation larvae web and feed on the flower clusters. In July and August, second-generation larvae feed on green berries. Young larvae penetrate the berry and hollow them out, leaving the skin and seeds. By September third-generation larvae cause great damage by webbing and feeding inside berries and within bunches, which become contaminated with frass (excrement).
Since 2009, the USDA, CDFA, County Agricultural Commissioners, UC Cooperative Extension and grape growers throughout the state have implemented a detection, quarantine, and treatment program with the goal of eradicating this insect from California. From a peak regulated area of 2,091 mi2 that included parts of 10 counties and 150,760 vineyard acres, the area has shrunk to 687 mi2 and includes 49,312 vineyard acres, mainly in Napa County. The aggressive mating disruption and insecticide program combined with statewide detection trapping efforts were responsible for the dramatic decreases in population. In 2010, over 100,000 males were caught in detection traps, compared with only 1 moth in 2014, and so far no moths have been detected in 2015.