Submitted to: Annals of the Entomological Society of America
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/20/2014
Publication Date: 7/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59374
Citation: Roehrdanz, R.L., Sears Wichmann, S.G. 2014. Wolbachia multilocus sequence typing of singly infected and multiply infected populations of Northern Corn Rootworm (Coleoptera: Chrysomelidae). Annals of the Entomological Society of America. 107(4):832-841. Interpretive Summary: The northern corn rootworm (NCR) is one of two rootworm species that is prevalent across the Corn Belt of the USA. It is most damaging in the western part of the Corn Belt where it has evolved the ability to survive as an egg for more than one winter and thus compromise control programs based on crop rotation. Reproductive and genetic barriers have been identified across the distribution range of NCR. Infection by a bacteria, Wolbachia, that lives within the insects cells is the primary agent involved in the reproductive barrier. NCR from central Illinois to the east are infected while those to the west are not. The central Illinois population is infected with a single strain of the bacteria but NCR from eastern Illinois to Pennsylvania are infected with multiple Wolbachia strains. DNA sequences of one of the Wolbachia genes, wsp, have previously indicated that at least five genetically distinct strains are present. The research uses a standard Multilocus Strain Typing (MLST) analysis to describe the different strains of Wolbachia that are present. The results highlight the drawbacks of the MLST system when individual insects are infected with several strains of Wobachia.
Technical Abstract: The northern corn rootworm (Diabrotica barberi) in eastern and central North America exhibits at least three distinct populations with respect to Wolbachia infection: uninfected; singly-infected; multiply-infected. The infected states are associated with different mtDNA haplotypes and reduced mtDNA variability. Multi locus strain typing (MLST) was used to define strain types and examine the diversity of Wolbachia infecting northern corn rootworm. DNA segments were amplified, cloned, and sequenced from each of the five MLST loci. Maximum composite likelihood was used to identify clusters of sequences. Four of the five MLST genes (coxA, hcpA, fbpA, ftsZ) were represented by three alleles each. The remaining MLST gene (gatB) had four to six alleles. The uncertainty arose from whether to call two small clusters new alleles or artifacts of the amplification process. Singly infected individuals had a common set of alleles that defined one strain (wBarB). This strain was also a component of the multiple infections. A second strain (wBarA), restricted to the multiple infections, was defined by alleles that appeared with substantially greater frequency for each of the five loci. By default a third strain would comprise the less frequent third allele of the four loci, but it is not possible to determine to which gatB allele they are linked. Therefore the strain is not fully defined. The diversity of gatB indicates that four to six Wolbachia strains are present in northern corn rootworm, a number that is similar to the five variants reported previously for the wsp gene. These results also highlight the very real difficulty of using the MLST system to define specific strains in a multiply-infected host.