Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 10/5/2005
Publication Date: 12/5/2005
Citation: Groves, R.L., Chen, J. 2005. Epidemiology of Pierce's Disease in the Central San Joaquin Valley of California: Factors Affecting Pathogen Distribution and Movement. Proceedings of the 2005 Pierce's Disease Research Symposium. p. 22-25.
Interpretive Summary: The glassy-winged sharpshooter (GWSS), a primary vector of Xf responsible for PD and ALSD, was introduced into Southern California around 1990 and has continued to expand its range in the state and is becoming widely distributed. We identified where the vector(s) acquire the pathogen, determined when vectors move into vineyards and characterized the populations of pathogen carried by GWSS. Host plant species significantly influenced GWSS population biology from samples collected 2003-05. GWSS adult, nymph, and egg mass densities varied among sweet cherry, navel, lemon, olive, avocado, peach, plum, pomegranate, pistachio, and grape. Adult GWSS were found in a wide range of crops with the largest populations in citrus (lemon and navel) and pomegranate. Adult GWSS were also regularly observed feeding upon annual weeds surrounding orchard crops. Juvenile insects were not always present on the same perennial tree crops. Overwintering adult GWSS were found on citrus, pomegranate, avocado, plum, peach, and non-crop annual weed species. Adult GWSS captures were randomly distributed through citrus crops and more aggregated along field margins in many other perennial orchard crops. The presence of Xf in a subsample of vectors collected from different perennial crops and on non-crop varied over the season with higher proportions of Xf detected in overwintered, adult insects in spring seasons. Accurate knowledge of GWSS host utilization in the central San Joaquin Valley, where they acquire the pathogen, when they move into susceptible crops, and when they spread the pathogen is critical to understanding and managing the spread of Xf diseases.
Technical Abstract: The primary objective of this research was to characterize the seasonal abundance, dispersal, and overwintering biology of the glassy-winged sharpshooter (GWSS), a primary vector of Xylella fastidiosa (Xf). Moreover, to identify where the vector(s) acquire the pathogen, to determine when vectors move into vineyards and transmit the pathogen to grapes, and to genetically characterize the populations of Xf isolated from GWSS collected in different perennial cultivated and non-cultivated plant species. Based on results of seasonal plant utilization by GWSS in our study through the winter of 2003-04 and into the subsequent growing season, we conclude that host plant species can significantly influence GWSS population biology. GWSS adult, nymph, and egg mass densities varied among perennial, cultivated crop plant species and non-cultivated weed species examined in this study. Perennial crop species examined included sweet cherry, navel, lemon, olive, avocado, peach, plum, pomegranate, pistachio, and grape. Adult GWSS dispersed into and fed upon a wide range of these crop species with the largest dispersing populations observed in citrus (lemon and navel) and pomegranate, similar to our findings in 2003. Adult GWSS were also regularly collected from and observed feeding upon a wide range of non-crop weed species within and surrounding experimental orchard crops. Nymph populations were not equally represented across all perennial tree crops with increased populations collected from citrus, pomegranate, and also non-crop annual weed species. Overwintering adult GWSS were consistently collected in relatively low population densities on citrus, pomegranate, avocado, plum, peach, and non-crop annual weed species. Patterns of adult GWSS capture among the distances sampled along linear transects extending into perennial crops were dissimilar among perennial crops. The presence of Xf in a subsample of GWSS collected among different perennial crops and on non-crop species was determined for collections in 2004 using PCR formats and the frequency of Xf detection in populations of GWSS varied among season in 2004.