EUSCELIDIUS VARIEGATUS iflavirus 1: insect-to-insect transmission

Euscelidius variegatus Kirschbaum (Hemiptera Cicadellidae) is a well-known leafhopper vector of phytoplasmas. A new member of a new species of the genus Iflavirus was recently discovered during transcriptomic analyses of a laboratory population of E. variegatus, and named E. variegatus virus 1 (EVV1). EVV1 infection was asymptomatic, and the virus was constantly detected both in phytoplasma exposed and not exposed vectors. Interestingly, virus load was significantly lower in the former category. Two other E. variegatus populations from France and US were found to be virus free (EVV1-), and one virus free population was therefore established in our lab starting from the French one. As Iflaviruses are generally known to infect the midgut of insects, preliminary in situ hybridization experiments confirmed EVV1 localization in the gut of E. variegatus, and this observation suggested that the virus might be secreted in the honeydew by infected leafhoppers. A protocol was then adapted from the available literature and the results confirmed the presence of EVV1 in the honeydew of infected insects. Horizontal transmission of the virus to the virus-free population was then tested through either artificial feeding on honeydew-contaminated feeding medium or through feeding on virus-contaminated plants from EVV1+ rearings. EVV1 was also found in the eggs of the virus-infected population, suggesting vertical transmission to the progeny. Individuals of the EVV1population were positive for virus presence, following abdominal microinjection with crude sap obtained by crushing of EVV1+ insects. Phytoplasma vector ability of EVV1+ and - populations with the same genetic background will be carried out to provide clues on the possible three-way interactions among insect/virus/phytoplasma. The production of an infectious EVV1 clone to express heterologous genes in the leafhopper and manipulate the expression of endogenous genes by virus-induced gene silencing is ongoing.