Horizontal Wolbachia Transmission in Cherry Fruit Flies

The eastern cherry fruit fly Rhagoletis cingulata was recently introduced to Europe were it co-infests cherries with the native European cherry fruit fly Rhagoletis cerasi. The shared habitat of the two insect species resulted in the horizontal transmission of a Wolbachia strain from R. cerasi to R. cingulata. Additionally specific R. cerasi populations are infected by a Wolbachia strain that is present in R. cingulata. Thus, the two fruit fly species provide a unique opportunity to resolve the dynamics of a horizontal transfer of Wolbachia in nature.

Our research objective will be accomplished by whole genome sequencing of different Wolbachia strains to precisely characterize their identities and relatedness. We will also trace the spatial and temporal distribution of the newly acquired endosymbiont in natural populations and test for reproductive effects on their hosts through laboratory crosses. Finally, we will determine the introduction routes of R. cingulata by performing extensive genomic characterization of native and invasive fly populations. Our joint study of Wolbachia and its native and invasive Rhagoletis hosts will provide novel insights into the early stages of Wolbachia transmission, the spread of the endosymbiont in nature and the consequences of the new infection for the fly.

In cooperation with: Christian Stauffer, Boku, Vienna; Jeff Feder, University of Notre Dame, USA; Lisa Klasson, Uppsala University, Sweden

Population genomics of vectors of phytoplasma

Phytoplasmas are bacteria responsible for a wide range of plant diseases. These bacteria are transmitted by sap-sucking insects, especially jumping plant lice. Apple proliferation is a phytoplasma disease of apple trees in Europe. While several different psyllids occur in apple orchards, just the two species Cacopsylla picta and Cacopsylla melanoneura are known to transmit phytoplasma with varying transmission efficiencies among regions. Moreover, these species showed regional differences in phytoplasma transmission efficiency.

We aim to address the question of what causes different phytoplasma transmission efficiencies. By using population genomic tools we will study the tripartite interaction between the phytoplasma, the vector, and its microbiome which will provide novel insights into the complex biology of Phytoplasma transmission.

In cooperation with: Christian Stauffer, Boku, Vienna; Katrin Janik, Research Centre Laimburg, Italy; Rosemarie Tedeschi, University of Turin, Italy; Omar Rota-Stabelli, Fondazione Edmund Mach, Italy

The role of bacteria and fungi in the population dynamics of the European spruce bark beetle in the Dolomites

The European spruce bark beetle Ips typographus is one of the most important forest pests. In autumn 2018, the storm "Vaia" and heavy snowfall in autumn 2019 caused severe damages in spruce forests in the Alpe-Adria region. Favorable temperature conditions and high amounts of suitable breeding material are main drivers of bark beetle population dynamics. The association with fungi and bacteria is a potential additional – yet understudied factor – influencing the aggressiveness of the European spruce bark beetle.

Therefore we are currently characterizing the fungal and bacterial symbionts of outbreaking and non-outbreakgin populations of I. typographus to understand their role in the invasion dynamics of the current outbreak in the Alpe-Adria region.

In cooperation with: Christian Stauffer and Martin Schebeck, Boku, Vienna; Massimo Faccoli and Andrea Battisti, Università degli Studi di Padova

Wolbachia in Rhagoletis species

Rhagoletis pomonella is a textbook example of ecological speciation by adaptation to different hosts. The recent shift of one population from the native hawthorn to the introduced domestic apples has resulted in the formation of an ecological and genetically different host races. Likewise, the closely related sister species R. mendax (blueberry maggot), R. zephyria (snowberry maggot) and the undescribed flowering dogwood fly speciated through adaptation to different hosts. In contrast, species of the Walnut-infesting R. suavis species group speciated due to allopatric divergence. The six species are largely allopatric, but do display parapatry in parts of their respective ranges. Finally, cherry fruit flies in the R. cingulata group appear to have speciated through a variety of modes. While R. cingulata and R. indifferens speciated due to allopatric separation, R. chionanthi and R. osmanthi speciated due to adaptation to different hosts.

Currently we are characterizing the Wolbachia community in the different Rhagoletis species. This will show if the bacterium has a coevolutionary history with its host or if different species harbor different strains with potential origin of independent horizontal transmission events.

In cooperation with: Jeff Feder, University of Notre Dame, USA

Wolbachia in Rhagoletis attacking parasitoids

Rhagoletis sp. are hosts of a broad range of different parasitoids. The community of parasitoid wasps that specializes in attacking Rhagoletis flies is a potential vector for horizontal transfer. These parasitoids directly oviposit their eggs into fly eggs or larvae, possibly acting as an infective hypodermic needle.

We are currently characterizing the Wolbachia infection in different Rhagoletis-infesting parasitoids and compare it with those of their hosts. Resolving the distribution of Wolbachia in braconid wasps will contribute to an explanation for the current distribution of Wolbachia in Rhagoletis and help reveal whether different strains may serve as an incompatibility barrier between parasitoids attacking different hosts or between multiple geographic populations.

In cooperation with: Jeff Feder, University of Notre Dame, USA; Glen Hood, Wayne State University, USA