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

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 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 

The olive fly, Bactrocera oleae is the most destructive pest of olives in the whole Mediterranean basin and represents the major threat to olive production worldwide. Strategies to control this pest species rely mainly on the use of conventional chemical pesticides whereas sustainable approaches are currently inefficient. Bactrocera oleae is living in close relationship with a microbial symbiont which is required for the larval development. 

In this project we test an innovative control strategy focusing on the manipulation of obligate bacterial symbionts of these pest species. Symbionts of the olive fly undergo an environmental phase, on the egg surfaces, prior to the acquisition by the newborns, becoming a good target for the application of the anti-symbiotic agents. The objective of the present project is to assess the microbial community of B. oleae and characterize the functional properties of primary symbionts using a whole genome approach. Our project will provide novel insights into the role of microorganism diversity in B. oleae fitness and to implement a novel control strategy based on symbiosis disruption.

In cooperation with: Isabel Martinez-Sanudo and Luca Mazzon Università degli Studi di Padova

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