Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 13, 2004
Publication Date: February 8, 2005
Citation: De Leon, J.H., Jones, W.A. 2005. Genetic differentiation among geographic populations of Gonatocerus ashmeadi (Hymenoptera: Mymaridae), the predominant egg parasitoid of Homalodisca coagulata (Homoptera: Cicadellidae). Journal of Insect Science. 5:1-9.
Interpretive Summary: Correctly identifying insects, both pests and natural enemies, is critical to a biological control program. Determining geographic variation may also be important since it may be an indication that biological differences may exist among populations. Releasing misidentified natural enemies could cause the biological control 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, DNA fingerprinting was performed on six geographic populations of Gonatocerus ashmeadi, the predominant egg parasitoids of the glassy-winged sharpshooter. The results of the study indicated that the geographic populations were highly differentiated. These data could be important because there may be one geographic population that is best suited for the environment in California.
In the present study ISSR-PCR was utilized to estimate the population genetic structure of Gonatocerus ashmeadi (Girault), the predominant egg parasitoid of Homalodisca coagulata (Say), the glassy-winged sharpshooter. Six populations from throughout the U. S. and a population from Argentina identified as near G. ashmeadi were analyzed. Four populations [California, San Antonio, TX, Weslaco, TX (WTX-2), and Florida] were field collected and two [Louisiana and Weslaco, TX (WTX-1)] were reared. Three ISSR-PCR reactions were pooled to generate 41 polymorphic markers among the six U. S. populations. Nei's expected heterozygosity values (h), including the reared population from Louisiana were high (9.01-14.3%) for all populations, except for a reared population from WTX-1 (2.9%). The total genetic diversity value (Ht) for the field populations was high (23%). Interestingly, the Florida population that was collected from one egg mass (siblings) generated the greatest number of polymorphic markers (20) and was observed with the highest gene diversity value (14.3%). All populations, except WTX-2 generated population-specific markers. Comparison of genetic differentiation estimates, which evaluate the degree of genetic subdivision, demonstrated good agreement between GST and ' values, 0.38 and 0.50, respectively for field populations, and 0.44 and 0.50, respectively for all populations. Genetic divergence indicated that the WTX-1 population was the most differentiated. Average divergence (D) results from the Argentina population support the taxonomic data that it is a different species. The present results estimate, for the first time, the population genetic structure of G. ashmeadi, demonstrating profound genetic divergence/structuring and restricted gene flow (Nm = 0.8295) among populations.