Submitted to: Annals of the Entomological Society of America
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/2/2011
Publication Date: 9/1/2011
Citation: Roehrdanz, R.L., Bourchier, R., Cortilet, A., Olson, D.L., Sears, S. 2011. Phylogeny and genetic diversity of flea beetles (Aphthona sp.) introduced to North America as biological control agents for leafy spurge. Annals of the Entomological Society of America. 104(5):966-975. DOI: 10.1603/AN10145. Interpretive Summary: In the late 1980s and early 1990s five species of flea beetles were brought from Europe to North America in an effort to suppress populations of the rangeland weed, leafy spurge. We used DNA markers to look at the genetic diversity of the flea beetles captured at various sites in the USA and Canada. Generally greater genetic diversity gives a population the opportunity to adapt to a wider range of local conditions. Because the beetles in North America originated from a relatively small number imported from Europe there is a chance that the genetic diversity was reduced in the process of importation and survival in North America. Unfortunately there is no genetic data available from the time of the original releases. We found that about 3/4 of the population of the most common brown flea beetle species has potentially reduced genetic variability due to a bacterial infection. We also found that the common black species has very little diversity in the USA but shows extensive diversity in Canada. One Canadian population is so divergent that it could be another species. This population might be effect in controlling leafy spurge at some sites where the other populations and species have not done well.
Technical Abstract: A molecular phylogeny is presented for the five main species of Aphthona flea beetles that were introduced to North America in conjunction with the leafy spurge biological control program. The mitochondrial genome was examined using PCR-RFLP of a 9000 bp segment and nucleotide sequencing of a 575 bp piece of cox1-cox2. A Neighbor Joining tree of the RFLP data, along with Neighbor Joining and Maximum Parsimony trees of the sequence alignments, all had the same major branching pattern. Each of the recognized species was a well defined clade. Three within species sub branches had very limited mtDNA diversity. One was a Wolbachia infected lineage of A. nigriscutis most likely generated by a Wolbachia sweep. Two of three subclades of A. lacertosa also had very little genetic diversity. One of these also displayed a divergence from the other two, similar to the divergence between some of the other species pairs, making it a legitimate candidate for a cryptic species. Its distribution was restricted to Canada. The other genetically depauperate A. lacertosa line was the only lineage recovered in the USA. The geographically restricted nature of some of the genetic lines could be exploited to redistribute them to other locations. It remains to be determined if either Wolbachia infection or a narrow genetic base has any detrimental effect on biological control.