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. 2004. Molecular distinction between populations of Gonatocerus morrilli, egg parasitoids of the glassy-winged sharpshooter, from Texas and California: Do cryptic species exist? In: Proceedings of the CDFA Pierce's Disease Control Program Research Symposium, December 7-10, 2004, San Diego, California. p. 318-321.
Interpretive Summary: Gonatocerus morrilli is an egg parasitoid of the glassy-winged sharpshooter (GWSS). This primary egg parasitoid species is common in the southern United States and Mexico. A biological control program is currently in progress in California against the GWSS, which is a serious economic pest that transmits 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. This study uses sophisticated genetic techniques to distinguish between geographic populations of G. morrilli from Texas and California. Results will facilitate ongoing efforts to develop more effective biological control programs for the GWSS.
Two molecular methods were utilized to distinguish geographic populations of Gonatocerus morrilli (Howard) from Texas and California and to test the possibility that this species could exist as a species-complex. Inter-Simple Sequence Repeat-Polymerase Chain Reaction (ISSR-PCR) was performed with a 5'-anchored ISSR primer. Twenty-five markers were generated with four populations (40 individuals) of G. morrilli, 23 were polymorphic and percentage of polymorphic loci was 92%. Most markers could be considered diagnostic since there was no band sharing between the Texas and California populations. Such differences typically are not found unless the populations are reproductively isolated. Exact tests for population differentiation indicated significant differences in markers frequencies among the populations. Comparison of other genetic differentiation estimates, which evaluate the degree of genetic subdivision, demonstrated excellent agreement between GST and ' values, 0.92 and 0.94, respectively; indicating that about 92 to 94% of the variance was distributed among populations. Average genetic divergence (D), as measured by genetic distance, was extremely high (Nei = 0.82 and Reynolds = 2.79). A dendrogram based on Nei's genetic distance, separated the Texas and California populations into two clusters, respectively. Amplification of the Internal Transcribed Spacer-1 (ITS-1) region showed no size differences, whereas the ITS-2 DNA fragments varied in size between the two geographic populations. The ITS-2 fragment sizes were about 865 and 1099 base pairs for the California and Texas populations, respectively. The present study using the two molecular methods provides novel data critical to the glassy-winged sharpshooter/Pierce's disease biological control program in California.