Title: MOLECULAR DISTINCTION BETWEEN POPULATIONS OF HOMALODISCA COAGULATA (HOMOPTERA: CICADELLIDAE) EGG PARASITOIDS, GONATOCERUS MORRILLI (HYMENOPTERA: MYMARIDAE), FROM TEXAS AND CALIFORNIA, DOES A CRYPTIC SPECIES EXIST?
Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 2004
Publication Date: December 3, 2004
Citation: De Leon, J.H., Jones, W.A., Morgan, D.J. 2004. Molecular distinction between populations of Gonatocerus morrilli, egg parasitoids of the glassy-winged sharpshooter Homalodisca coagulata, from Texas and California, Do cryptic species exist? Journal of Insect Science. 4:7.
Interpretive Summary: Correctly identifying insects, both pests and natural enemies, is critical to a biological control program. Releasing misidentified natural enemies could cause the biocontrol program to fail. A biological control program is underway in California against the glassy-winged sharpshooter because this insect threatens the wine and table grape industry ($33 billion) in this state. In the present study two molecular methods were utilized to distinguish geographic populations of Gonatocerus morrilli from California and Texas. Gonatocerus morrilli is an egg parasitoid of the glassy-winged sharpshooter. The results of the data demonstrate that the populations from California and Texas are genetically distinct and therefore the possibility that these natural enemy populations are cryptic species exists. The fact that these populations of G. morrilli are genetically distinct is critical because they may have different efficacies in attacking the glassy-winged sharpshooter.
In the present study, 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, twenty-three 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 marker frequencies among the populations. Comparison of other genetic differentiation estimates, which evaluate the degree of genetic subdivision, demonstrated excellent agreement between GST and ' values, 0.922 and 0.941, 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 = 0.823 and Reynolds = 2.790). A dendrogram based on Nei's genetic distance, separated the Texas and California populations into two clusters, respectively. Amplification of the Internal Transcribed Spacer region, ITS-1 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 results of the present study with the two molecular methods are novel data critical to the glassy-winged sharpshooter/Pierce's disease biological control program in California.