|Sears Wichmann, Sheila|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2005
Publication Date: 4/1/2006
Citation: Roehrdanz, R.L., Olson, D., Bourchier, R.S., Sears, S., Cortilet, A.B., Fauske, G.M. 2006. Mitochondrial DNA diversity and Wolbachia infection in the flea beetle Aphthona nigriscutis (Coleoptera: Chrysomelidae): An introduced biocontrol agent for leafy spurge. Biological Control. 37(1):1-8. Interpretive Summary: Several species of flea beetles from the genus Aphthona have been introduced into North America since the late 1980s in an effort to control the invasive rangeland weed, leafy spurge. Both the plants and the insects are natives of Eurasia. The introduced beetles have been quite effective in reducing spurge at many sites. Aphthona nigriscutis is the most successful and widely distributed brown leafy spurge flea beetle. As the beetle populations have been expanded and dispersed it has been observed that they fail to become established at some spurge infested locations. There could be many reasons for this including species differences in habitat and dispersal preferences, reduced genetic diversity within species tracing back to the original beetle collections in Europe, or local variation in the spurge. We have conducted the first mitochondrial DNA survey of genetic diversity of A. nigriscutis in North America. We found two distinct genetic groups that appear to be broadly co-mingled at most locations and we did not find any evidence that the overall genetic diversity in this species was unusually low. We also report some gene sequences from a bacteria (Wolbachia) associated with one of the two beetle genetic groups. The bacterial DNA sequences place this strain in the Wolbachia Supergroup A, one of two Supergroups that are widely distributed among insects. The bacteria is most likely responsible for a female dominated sex ratio that has been reported for this species at some locations over the years since its introduction.
Technical Abstract: Aphthona nigriscutis is one of several species of Aphthona flea beetles that have been introduced into North America in an effort to control the weed, leafy spurge (Euphorbia esula). It has been a very effective biological control agent at some locations but not at others. Overall genetic diversity is one parameter that could have an effect on successful establishment at specific locations. We have examined the genetic diversity of mitochondrial DNA in selected populations of A. nigriscutis. The results indicate that the insects are divided into two mtDNA clades. About 78% of the individuals comprise a clade (A) that has little or no mtDNA diversity. The remaining insects in the other clade (B) display extensive diversity with 15 haplotypes observed. The two subpopulations co-exist at most locations. The bacterial endosymbiont Wolbachia has been discovered in some individuals. About 86% of the individuals from mtDNA clade A tested positive for Wolbachia. Portions of the Wolbachia ftsZ and wspA genes were sequenced and the sequences have been shown to fall within the Wolbachia Supergroup A. None of the insects from clade B appear to be infected. The association of Wolbachia in one, but not both, mtDNA clades, can explain the female dominated sex ratio in some samples of A. nigriscutis and may play a role in limiting genetic diversity within beetle populations.