Role of the Blue-green Sharpshooter, Hordnia circellata , 1 in the Epidemiology of Pierce's Disease of Grapevines 2

Abstract

Yellow sticky trap and transect foliar sampling were used to study the spatial distribution of the blue-green sharpshooter, Hordnia circellata (Baker), in and near vineyards infected with Pierce's disease. From April through June, adults concentrated most heavily in riparian vegetation and within vineyards on grapevines nearest riparian vegetation. The spatial pattern of nymphal distribution reflected early season movements of females in grapes. Adults Were more evenly distributed within vineyards after midgrowing-season. The percentages of sharpshooters collected from vineyards plots and tested for their ability to transmit the causal agent of Pierce's disease to test grape plants rose from 13% in July 1972 to 45% the following June. In 1973, infectivity increased from 30% in July to 45% in September. Of sharpshooters collected from areas of vineyard plots where the incidence of Pierce's disease was below 5%, 14% were Infections in 1972 and 33% in 1973. The early season distribution of sharpshooters in vineyards coincided in many ways with the pattern of Pierce's disease. After mid-season, the pattern of sharpshooter distribution varied widely from that of Pierce's disease.