|De Leon, Jesus|
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2004
Publication Date: 7/1/2004
Citation: De Leon, J.H., Jones, W.A., Morgan, D.J. 2004. Population genetic structure of Homalodisca coagulata (Homoptera: Cicadellidae) the vector of the bacterium Xylella fastidiosa causing Pierce's disease in grapevines. Annals of the Entomological Society of America. 97(4):1-10. Interpretive Summary: The glassy-winged sharpshooter (GWSS) is a xylem feeding insect that is a serious pest because it transmits a bacterial disease to grapevines known as Pierce's disease. The GWSS is native to the southern U. S. but within the last ten years, it has established in southern California. In the present study we used a DNA fingerprinting method (Inter-Simple Sequence Repeat-Polymerase Chain Reaction, ISSR-PCR) to 1) determine the origin of this insect now found in California, 2) determine genetic variation within and among populations, and 3) determine the population genetic structure of this insect. The results estimate, for the first time, the population genetic structure of the GWSS and suggest that a subset of insects in California may have their origins in the southwestern region of the U. S. (Texas); furthermore, these results are suggestive of more than one founding event in California.
Technical Abstract: In the present study compound Inter-Simple Sequence Repeat (ISSR) primers containing CA/GT-repeat motifs in their sequences were utilized to estimate the population genetic structure of Homalodisca coagulata (Say). Eighteen populations from throughout the U.S. and a population from Tahiti, French Polynesia were analyzed. The 18 U.S. populations were arbitrarily assigned to three regions: southeastern, southwestern (Texas), and western (California) regions. A total of 62 and 91 neutral polymorphic markers were identified with p-15 and p-13, respectively. Exact tests for population differentiation indicated significant differences in marker frequencies among the 18 populations with both primers; in addition, significant differences were also observed within each region. Analyses of molecular variance (AMOVA) showed a significant partitioning of gene diversity among regions, 11% with p-15 and a lower value of 3% with p-13. The majority of the variance, however, were distributed within populations, 83 and 88% with p-15 and p-13, respectively. Comparison of other genetic differentiation estimates showed values for GST (8-11%) and ' (7-10%) for among regional variation that were of comparable magnitudes to the AMOVA results. A dendrogram based on Reynolds coancestry distance performed with p-15 clustered the U. S. populations into two main groups. The southeastern populations were grouped into one cluster and the southwestern and western populations into a second cluster. Within the western region, dendrograms produced with p-13 and p-15 showed in both cases that the Edison and Bakersfield populations clustered as outliers. The present results estimate, for the first time, the population genetic structure of H. coagulata and suggest that a subset of insects in California may have their origins in the southwestern region (Texas); furthermore, these results are suggestive of more than one founding event in California.