Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2007
Publication Date: 7/1/2007
Citation: Roehrdanz, R.L., Levine, E. 2007. Wolbachia bacterial infections linked to mitochondrial DNA reproductive isolation among populations of Northern Corn Rootworm (Coleoptera: Chrysomelidae). Annals of the Entomological Society of America. 100(4):522-531. Interpretive Summary: Wolbachia are a large group of bacteria that live inside the cells of many insects. They do not kill the insects whose cells they inhabit, which classifies them as endosymbionts. Wolbachia can create a reproductive barrier between insects of the same species that are infected versus those that are not infected. The northern corn rootworm (NCR) is a major pest of corn production. DNA markers have detected three genetically distinct populations of NCR in the US with relatively limited interbreeding between them. The agricultural community needs to be alert to the possibility that qualitative or quantitative differences may arise among these populations that could cause them to react differently to control measures. Wolbachia infections are also capable of spreading into uninfected areas which could change the distributions of specific NCR traits. Some unanswered questions for future research: Is Wolbachia infection expanding westward in NCR? Is one of the two incompatible Wolbachia strains gradually supplanting the other one? Is either infection associated with inherited differences, such as insecticide resistance or multi-year diapause, that could differentially affect control programs?
Technical Abstract: The endosymbiotic bacteria Wolbachia, has been detected in the northern corn rootworm (NCR, Diabrotica barberi) in the eastern half of the insect’s North American range. Using the Wolbachia 16S rDNA, ftsZ and wsp genes a boundary was identified in central Illinois, between infected and uninfected populations. Sequences of portions of the Wolbachia ftsZ and wsp genes have been obtained from several geographic locations of NCR. Within infected NCR populations two strains have been detected. The 1058 bp ftsZ sequences from NCR indicate that both strains belong to the Wolbachia Supergroup A. NCR Type I Wolbachia was found from eastern Illinois to Pennsylvania and is nearly identical (<0.3%) to the Wolbachia strain found in the western corn rootworm (D virgifera virgifera). NCR Type II Wolbachia occurs in central Illinois and differs by 3.1% from NCR Type I Wolbachia. The ~600 bp wsp sequences from the two strains are also dramatically different. NCR wsp Type I is identical to that from the western corn rootworm, while NCR wsp Type II differs by 63 substitutions (>10%) and 15 indels. The boundary between these two strains of Wolbachia in native populations of NCR correlates with a previously observed mtDNA genetic boundary in eastern Illinois suggesting that the two Wolbachia strains are incompatible and little if any introgression occurs between the two infected populations.