Silencing of ATP Synthase ß Impairs Egg Development in the Leafhopper Scaphoideus titanus, Vector of the Phytoplasma Associated with Grapevine Flavescence Dorée.

Scaphoideus titanus (Hemiptera: Cicadellidae) is the natural vector of Flavescence dorée phytoplasma, a quarantine pest of grapevine with severe impact on European viticulture. RNA interference (RNAi) machinery components are present in S. titanus transcriptome and injection of ATP synthase ß dsRNAs into adults caused gene silencing, starting three days post injection (dpi) up to 20 dpi, leading to decrease cognate protein. Silencing of this gene in the closely related leafhopper Euscelidiusvariegatus previously showed female sterility and lack of mature eggs in ovaries. Here, alteration of developing egg morphology in S. titanus ovaries as well as overexpression of hexamerin transcript (amino acid storage protein) and cathepsin L protein (lysosome proteinase) were observed in dsATP-injected females. To evaluate RNAi-specificity, E.variegatus was used as dsRNA-receiving model-species. Different doses of two sets of dsRNA-constructs targeting distinct portions of ATP synthase ß gene of both species induced silencing, lack of egg development, and female sterility in E. variegatus, indicating that off-target effects must be evaluated case by case. The effectiveness of RNAi in S. titanus provides a powerful tool for functional genomics of this non-model species and paves the way toward RNAi-based strategies to limit vector population, despite several technical and regulatory constraints that still need to be overcome to allow open field application.

Biological characterization of Euscelidius variegatus iflavirus 1.

Virus-based biocontrol technologies represent sustainable alternatives to pesticides and insecticides. Phytoplasmas are prokaryotic plant pathogens causing severe losses to crops worldwide. Novel approaches are needed since insecticides against their insect vectors and rogueing of infected plants are the only available strategies to counteract phytoplasma diseases. A new iflavirus, named EVV-1, has been described in the leafhopper phytoplasma vector Euscelidius variegatus, raising the potential to use virus-based application strategies against phytoplasma disease. Here transmission routes of EVV-1 are characterized, and localization within the host reveals the mechanism of insect tolerance to virus infection. Both vertical and horizontal transmission of EVV-1 occur and vertical transmission was more efficient. The virus is systemic and occurs in all life-stages, with the highest loads measured in ovaries and first to third instar nymphs. The basic knowledge gained here on the biology of the virus is crucial for possible future application of iflaviruses as biocontrol agents.

From DNA barcodes to ecology: Meta-analysis of central European beetles reveal link with species ecology but also to data pattern and gaps.

DNA barcoding has been used worldwide to identify biological specimens and to delimit species. It represents a cost-effective, fast, and efficient way to assess biodiversity with help of the public Barcode of Life Database (BOLD) accounting for more than 236,000 animal species and more than 10 million barcode sequences. Here, we performed a meta-analysis of available barcode data of central European Coleoptera to detect intraspecific genetic patterns among ecological groups in relation to geographic distance with the aim to investigate a possible link between infraspecific variation and species ecology. We collected information regarding feeding style, body size, as well as habitat and biotope preferences. Mantel tests and two variants of Procrustes analysis, both involving the Principal Coordinates Neighborhood Matrices (PCNM) approach, were applied on genetic and geographic distance matrices. However, significance levels were too low to further use the outcome for further trait investigation: these were in mean for all ecological guilds only 7.5, 9.4, or 15.6% for PCNM + PCA, NMDS + PCA, and Mantel test, respectively, or at best 28% for a single guild. Our study confirmed that certain ecological traits were associated with higher species diversity and foster stronger genetic differentiation. Results suggest that increased numbers of species, sampling localities, and specimens for a chosen area of interest may give new insights to explore barcode data and species ecology for the scope of conservation on a larger scale. We performed a meta-analysis of available barcode data of central European beetles to detect intraspecific genetic patterns among ecological groups in relation to geographic distance, regarding feeding style, body size, as well as habitat and biotope preferences. Our study confirmed that certain ecological traits were associated with higher species diversity and foster stronger genetic differentiation. However, significance levels were too low to further use the outcome for further trait investigation.

Bacteriophage-Host Association in the Phytoplasma Insect Vector Euscelidius variegatus.

Insect vectors transmit viruses and bacteria that can cause severe diseases in plants and economic losses due to a decrease in crop production. Insect vectors, like all other organisms, are colonized by a community of various microorganisms, which can influence their physiology, ecology, evolution, and also their competence as vectors. The important ecological meaning of bacteriophages in various ecosystems and their role in microbial communities has emerged in the past decade. However, only a few phages have been described so far in insect microbiomes. The leafhopper Euscelidius variegatus is a laboratory vector of the phytoplasma causing Flavescence dorée, a severe grapevine disease that threatens viticulture in Europe. Here, the presence of a temperate bacteriophage in E. variegatus (named Euscelidius variegatus phage 1, EVP-1) was revealed through both insect transcriptome analyses and electron microscopic observations. The bacterial host was isolated in axenic culture and identified as the bacterial endosymbiont of E. variegatus (BEV), recently assigned to the genus Candidatus Symbiopectobacterium. BEV harbors multiple prophages that become active in culture, suggesting that different environments can trigger different mechanisms, finely regulating the interactions among phages. Understanding the complex relationships within insect vector microbiomes may help in revealing possible microbe influences on pathogen transmission, and it is a crucial step toward innovative sustainable strategies for disease management in agriculture.

New Viral Sequences Identified in the Flavescence Dorée Phytoplasma Vector Scaphoideus titanus.

The leafhopper Scaphoideus titanus is the primary vector of Flavescence dorée phytoplasma (FDp) in European vineyards. Flavescence dorée is one of the most severely damaging diseases of Vitis vinifera and, consequently, a major threat to grape and wine production in several European countries. Control measures are compulsory, but they mainly involve large-scale insecticide treatments, with detrimental impacts on the environment. One possible solution is to exploit the largely unexplored genetic diversity of viruses infecting S. titanus as highly specific and environmentally benign tools for biological control. (2)Methods: A metatranscriptomic approach was adopted to identify viruses that may infect individuals caught in the wild in both its native (United States) and invasive (Europe) areas. Reverse transcription PCR was used to confirm their presence in RNA pools and explore their prevalence. (3)Results: We described nine new RNA viruses, including members of "Picorna-Calici", "Permutotetra", "Bunya-Arena", "Reo", "Partiti-Picobirna", "Luteo-Sobemo" and "Toti-Chryso" clades. A marked difference in the diversity and abundance of the viral species was observed between the US population and the European ones. (4)Conclusions: This work represents the first survey to assess the viral community of a phytoplasma insect vector. The possibility to exploit these naturally occurring viruses as specific and targeted biocontrol agents of S. titanus could be the answer to increasing demand for a more sustainable viticulture.