Submitted to: Annals of the Entomological Society of America
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/4/2013
Publication Date: 5/1/2013
Publication URL: http://handle.nal.usda.gov/10113/56439
Citation: Roehrdanz, R.L., Sears Wichmann, S.G. 2013. Wolbachia wsp gene clones detect the distribution of Wolbachia variants and wsp hypervariable regions among individuals of a multistrain infected population of Diabrotica barberi (Coleoptera: Chrysomelidae). Annals of the Entomological Society of America. 106(3):329-338. 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 has indicated that at least five genetically distinct strains are present. The strongest reproductive barrier appears to be between the populations infected with a single strain and those infected with multiple strains. It is possible that this barrier could inhibit the eastward spread of the extended overwintering trait.
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; multi-infected. The infected states are associated with different mtDNA haplotypes and reduced mtDNA variability. Sequences of the Wolbachia wsp surface protein gene indicated that multiple infections exist that include at least five distinct strains which are supported by both nucleotide analysis and digital translation alignments. The recovery of the different wsp hypervariable regions among 55 clones obtained with universal PCR primers from several individuals was unequal. The most common was obtained 33 times, the least common only once. One of the Wolbachia strains is present in both single infected and multiple infected individuals. Possible explanations for the frequency differences are that the frequency of each strain is not the same within each insect. An alternative possibility is that not all individuals are infected with all five strains and that different animals contain different combinations of the strains. The second scenario suggests that some strains are rare in the population. The two explanations are not mutually exclusive. Comparisons of the wsp genes with sequences in GenBank show that two of the strains are most similar to strains infecting subspecies of the congeneric western corn rootworm (D. virgifera virgifera and D. v. zeae). The most similar sequence to a third strain is found in a spider. Individual wsp hypervariable regions (HV)(some literature uses HVR for these regions) were also aligned with database sequences. The results provide evidence that some HVs are much more common than others and that the HVs can be shuffled to create new wsp genes.