The host range of the male-killing symbiont Arsenophonus nasoniae in filth fly parasitioids.

The Son-killer bacterium, Arsenophonus nasoniae, infects Nasonia vitripennis (Hymenoptera: Pteromalidae), a parasitic wasp that attacks filth flies. This gammaproteobacterium kills a substantial amount of male embryos produced by an infected female. Aside from male death, the bacterium does not measurably affect the host, and how it is maintained in the host population is unknown. Interestingly, this bacterial symbiont can be transmitted both vertically (from mother to offspring) and horizontally (to unrelated Nasonia wasps developing in the same fly host). This latter mode may allow the bacterium to spread throughout the ecological community of filth flies and their parasitoids, and to colonize novel species, as well as permit its long-term persistence. We tested 11 species of filth flies and 25 species of their associated parasitoids (representing 28 populations from 16 countries) using diagnostic PCR to assess the bacterium's actual host range. In addition to 16S rRNA, two loci were targeted: the housekeeping gene infB, and a sequence with high homology to a DNA polymerase gene from a lysogenic phage previously identified from other insect symbionts. We identified infections of A. nasoniae in four species of parasitoids, representing three taxonomic families. Highly similar phage sequences were also identified in three of the four species. These results identify the symbiont as a generalist, rather than a specialist restricted solely to species of Nasonia, and also that horizontal transmission may play an important role in its maintenance.

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.