Climate tolerances of Philaenus spumarius should be considered in risk assessment of disease outbreaks related to Xylella fastidiosa

Abstract

The bacterium Xylella fastidiosa (Xf) is an invasive insect-borne pathogen, which causes lethal diseases to important crops including olives, citrus, almonds and grapes as well as numerous forest, ornamental, and uncultivated plants. Outbreaks of Xf-related plant diseases are currently occurring in the Mediterranean region, causing substantial losses to various agricultural sectors. Several models have recently been published to identify which regions are at highest risk in Europe; however, such models did not consider the insect vectors, which constitute the key driver of short-range Xf spread. We fitted bioclimatic species distribution models to depict the macroclimatic preferences of the meadow spittlebug Philaenus spumarius L. (1978) (Hemiptera: Aphrophoridae), the major epidemiologically relevant vector currently responsible for Xf spread in the Europe. Many regions of Western Europe and Mediterranean basin are predicted by models as highly climatically suitable for this vector, including all regions where severe Xf have occurred so far. Conversely, the driest and warmest areas of the Mediterranean basin are predicted as little suitable for P. spumarius. Models forecast that agricultural-important parts of the southern Mediterranean area might experience a substantial decrease in climatic suitability for P. spumarius by the period 2040–2060. Areas predicted as highly suitable just for the bacterium but not optimal for this vector are apparently still free of severe Xf outbreaks, suggesting that climate tolerances of P. spumarius might partly explain the current spatial pattern of Xf outbreaks in Europe and should always be considered in further risk assessments.

Global predictions for the risk of establishment of Pierce’s disease of grapevines

“…Irrespective of vineyard distribution, we estimated that PD could potentially become established (i.e., r(t) > 0) at a maximum of 3.1% of the territory, while the area at moderate-risk index would be around 5-times lesser than the model without the vector's climate suitability layer, this latter more in consonance with other proposed risk maps [45,46]. Such differences in the projected risks are mainly concentrated in the warmest and driest Mediterranean regions and are due to uncertainties concerning temperature-humidity interactions in the ecology of the vector [35].…”

“…5). Nonetheless, our model projection for 2050 that includes spatial het-erogeneity in the vector distribution, as in Europe, would indicate a lower transmissibility because global change is predicted to have negative effects on P. spumarius abundance in Europe [35, 68]. At global scale, there is certain scientific consensus that climate change will follow a general pattern summarised in the paradigm “dry gets drier, wet gets wetter” [69].…”

“…S8). We used the positive relationship found between the climate suitability and abundance of P. spumarius adults [35] to assume no climatic constraints on vector population sizes at the optimal climatic conditions v = 1. Climatic suitability indices, v(x), were used to compute a spatially-dependent basic reproduction number, R 0 (x) = R 0 • v(x).…”

“…The model assumes a local Xf PD spatial propagation among plants mediated by the presence of potential vectors. Due to the limited knowledge about the vectors of PD in most wine-growing regions of the world [30], we employ fixed basic reproductive numbers (R 0 ) in the epidemiological models, except for Europe, where there are precise es-timations of climate suitability for the main vector P. spumarius [35]. This heuristic approach to obtaining PD risk maps yields results that are consistent with all the relevant data available [45].…”

Phenology, Seasonal Abundance, and Host-Plant Association of Spittlebugs (Hemiptera: Aphrophoridae) in Vineyards of Northwestern Italy

“…However, further studies on movements between host plants and feeding behavior are needed to assess the risk of secondary spread, since the preferred feeding sites on grapevines of the spittlebug could be located on the distal portions of stem, where Xf populations are usually low until midsummer, thus impairing efficient vine-to-vine transmission in the early season, the optimal period for establishing systemic infection [70]. Climate change could also play a two-faced role in shaping future Xf -grapevine scenarios in Europe as, on one hand, it could make several wine-producing regions more suitable to Xf establishment [53], while on the other, it could determine a northward shift of P. spumarius distribution, decreasing the suitability of southern European areas for this insect [72].…”