Wolbachia infection in natural populations of Dictyophara europaea, an alternative vector of grapevine Flavescence doree phytoplasma: effects and interactions

The European lantern fly, Dictyophara europaea, is an alternative vector of the Flavescence doree phytoplasma (FDp) disease of grapevine in European vineyards, enabling infection initiation from wild reservoir compartment (Clematis vitalba). Heretofore recorded rate of D. europaea FDp-infection has been very low (3%), making it less epidemiologically significant than would be expected based on reservoir plant infection rate (30%). In this study we present findings on a heavily FDp-infected D. europaea population (>60%), on the natural Wolbachia infection of populations with low FDp-infection rates (DeWo+) and on Wolbachia absence in highly FDp-infected population (DeWo-). We examine several possible causes underlying the differences in vector infection rates: (a) population genetic characteristics of D. europaea and correlation with Wolbachia strain wEur natural infections, (b) Wolbachia effects on fitness components of DeWo+ laboratory colony and (c) rate of reservoir plant FDp-infection and differences in FDp genotypes harboured by low and highly infected vector populations. The vector genetic diversity level was found to be lower in DeWo+ than in uninfected individuals and to exhibit a different evolution of fixed haplotypes. All DeWo+ populations were infected with the same strain of wEur. The FDp was found to be genetically diversified (five genotypes) but had no relation to infection rates. We did not find evidence of fitness upgrades with regard to Wolbachia infection status. Although more experimentation is needed, it seems that Wolbachia confers protection against FDp or is in competition with FDp according to the observed correlations: low FDp-infected vector populations are infected with Wolbachia and vice versa.