Results and Discussion (WP1)

Areas of potential establishment of GFD (based on the potential establishment of the vector) and grid distribution maps of GFD for Austria and European countries (M2)

The Ecoclimatic index (EI) integrates the annual growth index, which describes the potential for population growth, with the annual stress index that limit survival and with the thermal accumulation (PDD) during the developmental season. EI indicates the overall potential of a given location for establishment. The results of the CLIMEX modelling of the potential distribution of S. titanus in North America are presented in Figure 1: The species is known to be very abundant in the North-Eastern part of the USA, especially in the area around the great lakes. EI values in this area range from 20 and 29, indicating very good climatic conditions for establishment of S.titanus. The reported absence of S. titanus in British Columbia and Alberta in Canada as well as in Washington, Oregon, Nevada and Wyoming in the USA is accounted by very low EI values (e.g. EI of 5 in parts of Alberta, Washington, Oregon and Wyoming), indicating that S. titanus is unable to establish stable populations there. In Europe, S titanus is widespread in Northern Mediterranean areas: northeastern Spain, south of France, north of Italy, Slovenia, Croatia, moreover in Serbia and Hungary. All

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known distributions areas of S. titanus in these countries are indicated as being suitable in the model. Furthermore, areas where S. titanus is reported to be more abundant are indicated with high EI values e.g. EI up to 38 in Cotes-d’Azur in France (Aquitaine, Poitou-Charentes, Centre, Midi-Pyrenees, Languedoc-Roussillion, Provence-Alpes-Cotes-d’Azur and Rhone-Alpes) and in the north of Italy (EI up to 33). In some areas (e.g. the center of Spain, Greece) S. titanus could not establish; there the EI values are very low (1-9) due to low precipitation resulting in dry stress for S. titanus in this regions. Only in Catalonia EI values are high (EI up to 37) reflecting the suitable climate and presence of S. titanus as reported in the literature (Lavina et al. 1995; Batlle et al. 1997).

Figure 1: Geographical distribution of S. titanus in its native area in North America, CLIMEX results using grid-data model (resolution: 30’ longitude/latitude). The Ecoclimatic index (EI) indicates the overall potential of a location for establishment. The higher the EI, the more suitable a location is.

Figure 2 Predicted potential distribution of S. titanus in Europe under current climate conditions applying the CLIMEX software. (a) grid-data model (resolution: 10’ longitude/latitude).

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Risk maps of current climate and climate change (M3)

S. titanus feeds mainly on Vitis spp. (European and American Vitis spp) and requires grapevine for oviposition and completion of its life cycle. Grapevine is the major host plant of S. titanus and the endangered crop on which GFD phytoplasma causes significant economic impact. To define areas in which S. titanus would find suitable conditions for further establishment. the vine growing regions in Europe were combined with the EI values of the CLIMEX^® model and imported to a geographical information system to create composite risk maps (ArcGIS^® 10.0) (Figure 3).

Figure 3: Predicted potential distribution of S. titanus in Europe under current climate conditions modeled with the CLIMEX software combined with the vine growing areas in Europe (CLC 2006).

The projection of climatic suitability for S. titanus in Europe reveals that this species would be capable to establish in the east of Austria, south of the Czech Republic, Germany and Poland. Thus, the following vine growing regions are at high risk for the establishment of S.

titanus and GFD: (a) Germany: Mosel-Saar-Ruwer (11.500ha) as well as Rheinhessen, Pfalz and Baden (together about 76100ha), with EI values of 15-21; (b) In Austria, the largest vine growing regions that are located in the federal states of Lower Austria and Burgenland and contain 91.8% of the total Austrian vine growing area are highly suitable for S. titanus with EI values ranging from 15-24; (c) the vine growing areas in southern Moravia, in the Czech Republic, are climatically suitable with EI values of 15-19. In contrary, the majority of the vine growing areas in Spain are situated in less suitable regions (EI values ranging from 1-9).

CLIMEX^® allows estimating the impact of climate change on the occurrence of a species.

Different temperature and precipitation scenarios can be modelled and the effects in terms of changes in the distribution and abundance of a specific species can be examined. A1B-emission scenario was chosen from IPCC SRES which predicts a moderate GHG A1B-emission increase till 2100 with an increase in temperature of 2.8°C in average (IPCC, 2007). To

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generate climate conditions representing the climate conditions in 2100 according to the A1B-emission scenario the CLIMEX^® input parameters were adjusted: the minimum and the maximum average temperature in winter and summer was increased by 2.8° Celsius.

Generally, increasing winter and relieving summer precipitation are expected in the IPCC synthesis report. This was take into account in the CLIMEX modelling by increasing precipitation in winter by 20% and decreasing it in summer by 20%.

Figure 4: Predicted potential distribution of S. titanus in Europe under the climate conditions of A1B emission scenario modeled with the CLIMEX software.

Overall conclusion of the CLIMEX study:

Generally, CLIMEX proofed to be a useful tool to model the present distribution of S. titanus in North America and Europe as reported in the literature and to indicate areas not yet invaded by S. titanus that provide suitable climatic conditions for the establishment of this species. Regions where S. titanus is known to occur have a high EI value in the CLIMEX model, whereas areas where its absence is confirmed provide no growth or very low EI values (e.g. Nevada and Alberta in North America; Central Spain in Europe).

By combining the output data of the CLIMEX model with the host distribution in Europa, it was possible to define further vine growing areas with high risk of establishment of the vector species. Using this approach it became clear that the area climatically suitable for establishment of S. titanus extends over the present vine-growing area in Europe. S. titanus is currently established in the south of Europe but there is further scope of expansion to the north, e.g. northeast Austria, south of Czech Republic (Moravia and Bohemia) and to the west of Germany, where important connected vine growing areas are located.

The CLIMEX® modelling clearly shows that a prolonged summer would facilitate vector establishment and the development of stable populations in Central Europe. However, the establishment potential of S. titanus clearly exceeds the area where vine is grown in Central Europe. Therefore, it can be assumed that the limiting factor for spread of the vector is the distribution of the host plant Vitis vinifera. If, due to climate warming the production area of

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Vitis vinifera would expand to regions where formerly no vine was produced (Eitzinger, et.al, 2009), the vector species would find climatic conditions for establishment.