 It was not until 1915 that the relationship between the vector and the virus in causing disease was irrefutably established by P. A. Boucquet and W. J. Hartung.They showed that after leafhoppers taken from the wild with no previous contact with sugar beets were allowed to feed on beets, no disease ensued.But when they were allowed to feed on beets with symptoms of curly top for 3–7 days, curly top symptoms appeared on previously healthy beets after leafhoppers were transferred and granted time to feed.