Identifying local drivers of a vector-pathogen-disease system using Bayesian modeling

Abstract

‘Bois noir’ is a phytoplasma-mediated grapevine yellows disease that causes great economic damage in European vineyards. Previous studies have examined habitat relationships on a regional scale, which help to better understand the large-scale epidemiology. Local drivers, such as micro-habitat preferences of the vector (Hyalesthes obsoletus, a cixiid planthopper), or local interactions with reservoir host plants, however, are still poorly understood, although this knowledge is crucial for developing site-specific management strategies.Here, we examined the local environment-species relationships of a phytoplasma-mediated grapevine disease on a scale of 15m in a 2.9ha vineyard using: (i) data on elevation and habitat types; (ii) cover of host plants Urtica dioica and Convolvulus arvensis over three seasons, (iii) vector monitoring over four seasons; (iv) genetic tests for phytoplasma presence in the vector; and (v) inspection of 6056 grapevine plants for visual symptoms of the ‘bois noir’ disease. The data were analyzed in a joint causal model that describes the interplay between vector, pathogen, disease and environment, estimated with Bayesian inference.Our results indicate that surrounding natural and semi-natural vegetation (fallow land, forest and managed agricultural land) and high density of the major host plant U. dioica are associated with an increase in vector population densities. Higher vector population densities at low availability of U. dioica were associated with higher phytoplasma infection rates in the vector. The prevalence of disease symptoms in grapevine plants was nonetheless more affected by grapevine cultivar and higher elevation than by the estimated availability of infected vectors.The results of our local analysis support current bois noir management recommendations stating that (1) removal of the host plant U. dioica should be best carried out in either spring or autumn; and (2) grapevine cultivars are unequally susceptible. Moreover, we provide evidence that U. dioica control before the flight period may result in low U. dioica densities and high H. obsoletus population densities, causing an increase in vector infection rates and disease pressure.