|Sears Wichmann, Sheila|
Submitted to: International Wolbachia Conference
Publication Type: Abstract Only
Publication Acceptance Date: 6/27/2002
Publication Date: 7/30/2002
Citation: Roehrdanz, R.L., Levine, E., Degrugillier, S.S. 2002. A breeding barrier between populations of northern corn rootworm (Diabrotica barberi) in Illinois corresponds to infection by two different wolbachia types [abstract]. International Wolbachia Conference. p. 77-78.
Technical Abstract: The northern corn rootworm (NCR), Diabrotica barberi (Coleoptera: Chrysomelidae), is a significant pest of corn (maize) in the north central part of the USA. An examination of intraspecific geographic variability using PCR-RFLP of long amplicons revealed a strong east-west geographical partition of the observed mtDNA haplotypes. The line of demarcation is located in east central Illinois. The boundary zone is quite narrow and the eastern populations exhibit less overall variability than the western populations. 9 haplotypes were found east of the boundary, whereas 46 haplotypes were found to the west. Trees based on genetic distance measurements of the mtDNA produced two distinct clades. One clade contained all the eastern haplotypes along with a group of western haplotypes from the northern Great Plains. The other clade included the remaining western haplotypes. Since Wolbachia infections can establish breeding barriers, we determined to see if that might provide explanation for the sharp mtDNA divide. Clark et al. had reported that NCR from the Great Plains lacked Wolbachia. Using 16S rDNA primers we detected Wolbachia in NCR from the eastern portion of their range with a Wolbachia +/- boundary in central Illinois. That boundary is about 80 miles west of the mtDNA dividing line. Portions of the Wolbachia ftsZ and wsp genes have been sequenced from several geographic locations. The 1058 bp ftsZ sequences from NCR are Type A Wolbachia and fall into two groups (designated NCR Type I and II) within that category. NCR Type I Wolbachia from eastern Illinois to Pennsylvania are nearly identical (0.3% difference) to Wolbachia from western corn rootworm (WCR), Diabrotica virgifera, a related species that is also a corn pest. NCR Type II Wolbachia from central Illinois differ by 3.1% from Type I and are nearly identical to a Wolbachia found in the European raspberry beetle (0.1% difference). The ~600 bp wsp sequences are also dramatically different. NCR Type I is identical to that from WCR, while NCR type II differs by 63 substitutions (>10%) and 3 indels (15 bp). Restriction site differences between the two Wolbachias allowed assignment of a large number of individuals to NCR Type I or Type II. The boundary between these two very distinct strains of Wolbachia in adjacent geographical populations of NCR correlates with a previously observed mtDNA genetic boundary in eastern Illinois indicating that the two Wolbachias are incompatible and little if any introgression occurs between the two populations. There is currently no evidence that this boundary is being pushed in either direction. The boundary between the NCR Type II Wolbachia infected and uninfected insects appears to be less distinct. Unanswered questions: Is Wolbachia infection expanding westward in NCR? Is the identity of NCR Type I Wolbachia to Wolbachia from WCR more than coincidence? What about NCR Type II vs. the European strain? How long have these two opposing infections existed? Is either infection associated with inherited differences that could differentially affect control programs?