WHEN THE GRAPE integrated control project was started in 1961, the grape leafhopper, Erythroneura elegantula Osborn, was believed to be the primary pest of vineyards in the San Joaquin Valley. Also, it was believed that chemical treatments to control this insect were responsible for the increase of secondary pests such as spider mites. The basic aim of these studies was to determine what levels of leafhoppers could be tolerated without need of chemical treatments.