Multiple Wolbachia Infection in Rhagoletis cerasi

Wolbachia are inherited bacteria of arthropods which have attracted attention for their potential as biocontrol agents as they manipulate host reproduction by using e.g. cytoplasmic incompatibility (CI). Wolbachia strains of the cherry fruit fly were transferred to medfly and there wCer2 and wCer4 induced complete CI. However, during Wolbachia transinfection assays infected embryonic cytoplasm is transferred via microinjection into the recipient`s pole plasma and here other microorganism can be hidden passengers. Hence, the first part of this project aims to survey the microbial fauna of the reproductive organs of R. cerasi using degenerated 16S rDNA primers. Further novel Wolbachia strains of the Sicilian R. cerasi shall be characterized as detection of more strains is expected using various novel genetic marker sets (ANK, VNTRs, IS5). That way we will also obtain more information on (i) the genomic structure and organization of the different wCer strains and (ii) the genomic integrity and stability of recently established infections in novel host organisms. By transferring these Wolbachia strains to Drosophila simulans and D. melanogaster the phenotype and the infection dynamics of these Wolbachia strains shall be evaluated and information shall be won for their potential use in biological control.

Wolbachia are bacterial endosymbiont in insects and some other arthropod species as well as in nematodes. They are maternally inherited and colonize up to 76 % of all insect species. Wolbachia can change the reproduction in their host system ranging from feminization, parthenogenesis, male killing and most commonly cytoplasmic incompatibility (CI). CI results in reduced host offspring numbers or lethality of host embryos. Thus, Wolbachia have been considered potential candidates for the use in biological pest control management. Via transfer of CI- inducing Wolbachia strains in a nave host insect system, Wolbachia might be applied for the direct suppression of a pest population. The impact Wolbachia have on a host system makes a risk assessment inevitable. The integrity and stability of a de novo infection is of importance before artificially transferring Wolbachia into a nave host system. Wolbachia genomes vary considerably in their organisation and structure and hence are expected to be highly dynamic. The aims of this project were 1) to survey the microbial fauna of the reproductive organs of Rhagoletis cerasi 2) to uncover Wolbachia diversity and their titer dynamics in R. cerasi populations and 3) to study the genomic integrity and stability of recently established infections in novel host organisms. Diverse molecular approaches strongly imply that Wolbachia are the only symbiont associated with the germ line of natural R. cerasi populations. A re-screening of populations for new Wolbachia strains revealed the presence of at least five strains and all of the strains were characterized phylogenetically by multilocus strain typing. By transferring these Wolbachia strains into the model hosts of Wolbachia, Drosophila simulans and D. melanogaster, the phenotype and the infection dynamics of these Wolbachia strains were partly evaluated. These findings strongly imply the existence of high molecular turnover of Wolbachia in donor as well recipient lines, generating ancestral polymorphism plus de novo mutations.