A test using Wolbachia bacteria to identify Eurasian source populations of cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), in North America.

Previous research using mitochondrial haplotypes indicates that North American populations of cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), originated from at least two separate introductions from source populations in Eurasia. We tested this hypothesis by comparing the genetic variation of symbiotic Wolbachia bacteria in C. obstrictus among seven North American and four European populations. Because Wolbachia are maternally inherited, infections acquired by a host species at one geographic location theoretically may be present in derivative populations that have established in new regions. Use of the conserved MLST Wolbachia genes gatB, coxA, hcpA, fbpA, and ftsZ identified one strain present in all beetles. Use of the variable wsp gene identified three distinct isolates of this strain that appear to co-occur in all populations and potentially in all individuals. Use of the variable wspB gene provided independent support for the presence of these isolates and evidence of a wspB pseudogene. The lack of genetic variation for these Wolbachia genes among host populations prevents their use to clarify the origins of C. obstrictus in North America. However, the results are an interesting example illustrating disjunction in genetic variation between mitochondria and a maternally-inherited symbiont.