The dispersal, overwintering biology, and PCR detection of Xylella fastidiosa (Xf) in adult GWSS was determined. The incidence of Xf detection in dispersing GWSS populations did not vary among perennial, cultivated crop plant species (including sweet cherry, navel orange, Spanish lemon, olive, avocado, peach, plum, pomegranate, pistachio, and grape) while significant fluctuations in incidence were observed through two the seasons. Among a total of 5,432 adult GWSS examined, detection frequencies of Xf in dispersing adult GWSS varied over seasons in both years and peak incidence was detected in the months April through June. The incidence of Xf did not vary significantly among the nine crop species examined and mean detection frequency averaged 12.7% over all crops and dates. Very few Xf detections were observed in populations of adult GWSS collected through the summer months in either 2003 or 2004 representing recently emerged adult insects of the 1st generation. The incidence of Xf did not vary between adult sexes averaging 13.6 and 14.2 % between males and females, respectively across both years. Among the total of 688 adult GWSS in which Xf DNA was amplified, only 10.1 and 8.9 % of the extracted DNA was similarly amplified with strain-specific PCR primers representing grape and almond genotypes, respectively. Detailed information on the seasonal patterns of vector abundance, host plant use, and detection of Xf in dispersing populations of adult GWSS will help to accurately time and focus management efforts to reduce area-wide vector populations and limit the spread of Xf diseases.