Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: October 12, 2004
Publication Date: December 7, 2004
Citation: De Leon, J.H., Jones, W.A., Morgan, D.J.W., Mizell, R.J. 2004. Extensive sequence divergence in the ITS2 RDNA fragment in a population of Gonatocerus ashmeadi from Florida: Phylogenetic relationships of Gonatocerus species. In: Proceedings of the CDFA Pierce's Disease Control Program Research Symposium, December 7-10, 2004, San Diego, California. p. 309-312.
Interpretive Summary: Gonatocerus ashmeadi is a primary egg parasitoid of the glassy-winged sharpshooter (GWSS). A biological control program is currently in progress in California against the GWSS because this leafhopper is a serious economic pest that vectors a strain of bacterium that causes Pierce's disease in grapevines. Accurate identification of natural enemies is critical to the success of classical biological control programs. In this study, the Internal Transcribed Spacer regions (ITS-1 and '2) have been used extensively in genetic studies to examine the taxonomic status of species and for diagnostic purposes. The results will facilitate ongoing efforts to develop effective biological control programs for the GWSS.
The aim of the present study was to resolve the genetic relationships of geographic populations of Gonatocerus ashmeadi, a primary egg parasitoid of the glassy-winged sharpshooter. A phylogenetic approach was implemented by sequencing the Internal Transcribed Spacer-2 (ITS2) region of several individuals per population. In addition, the phylogenetic relationships of several Gonatocerus species were also determined. Six geographic populations of G. ashmeadi were analyszed: Quincy, FL (QFL), two populations from Weslaco, TX (WTXa and WTXb), Louisiana (LA), San Antonio, TX (SATX), and California (CA). The percentage divergence (%D) of the ITS2 sequences, as measured by genetic distance, was small among LA, SATX, and CA (0.10-1.10%); whereas, the %D for QFL vs these populations was extremely high (65.9-69.8%). A Neighbor-Joining distance tree separated the QFL population into a separate clade supported by very high bootstrap values (100%). When the Weslaco populations were included in the anaylsis, they clustered into two distinctive clades, WTXb clustered with QFL and WTXa clusterd with the rest of the populations; again very high bootstrap values (100%) supported the topology of the distance tree. These results indicate the present of sympatric strains in Weslaco. The phylogenetic analysis of several Gonatocerus species clustered the respective species into North and South American clades. The %D of the QFL population fell within the range (75.4-87.2%) of the South American Gonatocerus species and clustered within the South American clade. The present molecular phylogenetics results provide strong evidence that G. ashmeadi from Florida may be a different species. In addition, the data is suggestive that the origin of G. ashmeadi in California is the Texas region, including the closely located Louisiana. The findings of the present study are important to the glassy-winged sharpshooter/Pierce's disease biological control program in California.