Undergraduate Research Journal

Glassy-Winged Sharpshooter Population Survey and Xylella fastidiosa Detection
Candice A. Sanscartier
X. fastidiosa infection. Infections rates are relatively high
from July 23rd to September 3rd, the period corresponding
to what we believe is the 2nd active season generation, and
rates are high again from September 17th to October 15th,
the period that corresponds to the 3rd generation. However,
the weeks in which the infection rate was at 0 percent
may be due to the fact that very few to no GWSSs were
collected during those weeks and may not accurately show
the infection rates at the lowest points of each generation.
Figure 4. Weekly infection rate of GWSS collected from July 23rd
to October 29th.
Further studies are underway to investigate the full seasonal
occurrence of GWSS visitation to unsprayed grape plots
in Southern California and the rate of infection of X.
fastidiosa. The survey period will be extended to include
a potential early generation with the corresponding rates
of infection. Also we intend to obtain data on additional
factors possibly influencing GWSS visitation and infection
rates, such as sex, additional visiting sharpshooter species,
and grape variety. The described survey and future studies
will contribute to the body of knowledge regarding the
geographical and seasonal occurrence of the most prominent
vector of X. fastidiosa, GWSS. Understanding the insectpathogen-plant
host dynamics in the PD system is essential
to developing an effective method to control the disease.
This survey provides exceptional data on the seasonal
GWSS visitation and infection rates of X. fastidiosa and
establishes a foundation for additional studies.
CONCLUSION
This population survey consisted of a 15 week collection of
GWSS visiting a local, untreated grapevine plot from July
to October. The number of GWSS visiting the grapevines
was recorded weekly and the insect samples were analyzed
using real-time PCR and X. fastidiosa-specific primers to
detect infection with the pathogen responsible for causing
Pierce’s Disease in grapevines. The GWSS population
survey presented here demonstrates the presence of two
GWSS population generations at the AgOps grape plots.
Based on our knowledge of GWSS biology and the timing
of the survey, we conclude these are most likely the 2nd
and 3rd generations of 3 generation active season. The
overall rate of infection of X. fastidiosa among GWSS
visiting the AgOps plot was measured at 76%. This rate
appears uncharacteristically high compared to those of
previous population and infection rate studies (Hail et al.,
2010) but can be explained by the use of the more sensitive
real-time PCR technique for bacterial DNA detection. As
GWSS visitation appears cyclical, so does the X. fastidiosa
infection rate. X. fastidiosa infection rates correspond to
the visitation pattern seen in the population survey with
infection rates increasing and decreasing with population
generations. These low infection rates may represent an
actual fluctuation in infection frequency or they may due
to low numbers of GWSS collected on the corresponding
collection dates. Further studies will need to be performed
to confirm the cause of the cyclical infection rates.
This single season survey gives researchers information
about GWSS visitation patterns on local grapevines
and the rate of infection of X. fastidiosa in local GWSS
populations. This valuable data offers insight into the local
threat of Pierce’s disease and will be helpful in determining
control methods for the pest and bacterial vector, Glassy-
Winged Sharpshooter. This survey provides a foundation
for additional studies investigating GWSS visitation and
X. fastidiosa infection patterns. Continuation of this annual
survey will be helpful in understanding the dynamics of
Pierce’s disease and developing control measures for
GWSS and X. fastidiosa.
ACKNOWLEDGMENT
Funding for this project was provided by UCR’s
Undergraduate Research Grants program.
U C R U n d e r g r a d u a t e R e s e a r c h J o u r n a l 3 5