|De Leon, Jesus|
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2009
Publication Date: 1/12/2010
Citation: De Leon, J.H., Setamou, M. 2010. Molecular evidence suggests that populations of the Asian citrus psyllid parasitoid, Tamarixia radiata (Hymenoptera: Eulophidae), from Texas, Florida, and Mexico represent a single species. Annals of the Entomological Society of America. 103(1):100-110. Interpretive Summary: Tamarixia radiata is a natural enemy of the Asian citrus pysllid (ACP) (Diaphorina citri). ACP is an important world-wide economic pest of citrus that recently invaded Texas, among several other states in the U. S. In the present study, we genetically characterized populations of T. radiata from Texas, Florida, and Mexico by two molecular methods. The molecular data highly suggest that the three populations of T. radiata represent a single species. However, the data showed that the population of T. radiata in Texas did not come from Florida; rather, the data suggest that the population in Texas came from Mexico, or vice versa. The molecular data uncovered population-specific genetic variation that allowed the discrimination of the Florida and Texas/Mexico populations of T. radiata. In addition, the molecular data showed that no exchange of genetic material (gene flow) was occurring between the Florida and Texas/Mexico populations, while, exchange of genetic material was occurring between the populations of Texas and Mexico. This information is critical to the development of a biological control program against ACP in Texas. The data suggest that we may now have to take a different approach to biological control, especially since there is a possibility that T. radiata was already in Texas. If an imported natural enemy of the same species is released in Texas and it can reproduce with the native natural enemy, it may make it very difficult to track it to determine if it can establish due to the loss of its unique genetic variation. Thus, the current data highly suggest that more studies need to be performed before we release any natural enemies in Texas.
Technical Abstract: We genetically characterized Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) populations from Texas, Florida, and Mexico and a sister taxon T. triozae (Burks) by two molecular methods. T. radiata is an ectoparasitoid of Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae) nymphs. The populations were submitted to ISSR-PCR DNA fingerprinting with two primers. No fixed banding pattern differences were uncovered among the populations of T. radiata with either primer, while, different patterns were observed in T. triozae; thus suggesting that there is no genetic differentiation among the populations. Support for these results was obtained by sequence analyses of the internal transcribed spacer region 1 and the mitochondrial cytochrome oxidase subunit 1 (COI) gene. In both genes, the intra-populational variation range (percentage divergence, %D) fell within the inter-populational variation range. The %D at the COI gene between T. radiata and T. triozae was 9.0-10.3%. However, haplotype structure was uncovered among the populations. No haplotypes were shared between Florida and Texas/Mexico, while sharing was observed between Texas and Mexico. Two population-specific nucleotides were identified that allowed the discrimination of the Florida and Texas/Mexico individuals. A neighbor-joining and a parsimonious tree clustered the populations into two distinct clades. The Florida population clustered into clade 1, while the Texas/Mexico populations clustered into clade 2. The COI phylogeographic analysis suggests that the population of T. radiata in Texas did not come from Florida. Rather, the data suggests that the population in Texas came from Mexico, or vice versa, since the Mexico population showed less haplotype diversity.