4. Discussion

Results obtained in the present study are in line with our earlier prediction of CPB development under climate change in the Wielkopolska region, located in the western part of Poland [15]. In that study, two CPB generations were generated following a temperature increase of around 2C for the Wielkopolska region by a model developed on simulation results obtained using meteorological data registered at WinnaGóra, located 60 km south of Poznań, and data obtained after transformation of the recorded data to reflect a temperature increase of 1–6C. Similar results are presented in the present study for Poznań, where two generations of CPB are expected with a probability of 0.95 and 0.99 following a temperature increase of 1.9 and 2.3C, respectively. Comparison of the results of 16 models describing the influence of temperature rises on SGCPBP indicated that thermal conditions in south-western Poland are most similar to those that guarantee the appearance of two generations. On the other hand, an increase in the number of CPB generations in north-eastern Poland required a much higher temperature rise. The main advantage of the current study over the study published in 2013 is not only the increase in the number of localities but also the inclusion of four RCP scenarios, which enable an assessment of regional variations in climate change.

Simulation results produced with the use of RCP scenarios in the present study show that an increase in the number of CPB generations is very likely to appear in Poland. Under three (RCP4.5, RCP6 and RCP8.5) out of the four analyzed scenarios, average SGCPBP calculated for 16 localities is going to exceed 75% after 2039. The only scenario which shows that, at the end of the century, the situation will not differ very much from that observed in 1986–2005 is RCP2.6. However, even under that scenario, simulations showed a shortening of the CPB first generation development time, especially in the northern (Gdańsk), north-eastern (Olsztyn, Białystok), eastern (Lublin) and southern parts of central Poland (Kielce). The same regions were indicated as being the most vulnerable to shortening of the CPB first generation development from simulation results under scenarios RCP4.5, RCP6 and RCP8.5. Moreover, analysis of the pest development under scenarios RCP4.5, RCP6 and RCP8.5 showed that the second generation usually developed faster than the first generation. We decided not to compare the development time of the generations obtained in simulations on real data and under scenario RCP2.6 because of the excessive number of SGCPBP results lower than 50%.

generated the appearance of the second pest generation at Lublin and Białystok, respectively. At Kielce and Olsztyn, temperature rises of 2.5 and 3C were needed to trigger the appearance of the second generation, whereas at Gdańsk, the probability of the appearance of the second

With a probability of 99%, a temperature rise of 1.4C generated the second generation of CPB at Opole. At Katowice and Rzeszów, temperature had to increase by 1.9C. At Kraków, Szczecin and Wrocław, a 2C temperature rise triggered the appearance of the pest second generation. At ZielonaGóra and Łódź temperature had to rise by 2.2C. A temperature increase of 2.3, 2.4 and 2.5C generated the appearance of the second pest generation at Poznań, Toruń and Lublin. At Kielce and Białystok, temperature rises of 2.9 and 3.2C were needed to trigger the appearance of the second generation, whereas for Gdańsk and Olsztyn, the models did not generate the appearance of the second generation with a probability of 99%.

Results obtained in the present study are in line with our earlier prediction of CPB development under climate change in the Wielkopolska region, located in the western part of Poland [15]. In that study, two CPB generations were generated following a temperature increase of around 2C for the Wielkopolska region by a model developed on simulation results obtained using meteorological data registered at WinnaGóra, located 60 km south of Poznań, and data obtained after transformation of the recorded data to reflect a temperature increase of 1–6C. Similar results are presented in the present study for Poznań, where two generations of CPB are expected with a probability of 0.95 and 0.99 following a temperature increase of 1.9 and 2.3C, respectively. Comparison of the results of 16 models describing the influence of temperature rises on SGCPBP indicated that thermal conditions in south-western Poland are most similar to those that guarantee the appearance of two generations. On the other hand, an increase in the number of CPB generations in north-eastern Poland required a much higher temperature rise. The main advantage of the current study over the study published in 2013 is not only the increase in the number of localities but also the inclusion of four RCP scenarios,

Simulation results produced with the use of RCP scenarios in the present study show that an increase in the number of CPB generations is very likely to appear in Poland. Under three (RCP4.5, RCP6 and RCP8.5) out of the four analyzed scenarios, average SGCPBP calculated for 16 localities is going to exceed 75% after 2039. The only scenario which shows that, at the end of the century, the situation will not differ very much from that observed in 1986–2005 is RCP2.6. However, even under that scenario, simulations showed a shortening of the CPB first generation development time, especially in the northern (Gdańsk), north-eastern (Olsztyn, Białystok), eastern (Lublin) and southern parts of central Poland (Kielce). The same regions were indicated as being the most vulnerable to shortening of the CPB first generation development from simulation results under scenarios RCP4.5, RCP6 and RCP8.5. Moreover, analysis

which enable an assessment of regional variations in climate change.

generation did not exceed 93%.

76 Potato - From Incas to All Over the World

4. Discussion

As expected, the lowest values for SGCPBP were generated under scenario RCP2.6, whereas the highest were noted under RCP8.5. The SGCPBP values produced by the former are usually lower than 75%. That is why we did not use it to specify the regions to be threatened by CPB in the future. The values for SGCPBP produced by RCP8.5 are usually higher than 75%, but there are almost no differences in this analyzed parameter between localities, so this scenario was also not used for specification of the regions at most risk from CPB in the future. On the other hand, scenarios RCP4.5 and RCP6 can be helpful in identifying regions at risk from CPB in the future. Both produced quite differential results, usually higher than 75%. Comparison of simulation results obtained under scenario RCP4.5 enables identification of the south-western region (Opole, Wrocław), the south-eastern (Rzeszów), eastern (Lublin) and southern parts of central Poland (Kielce), as being the most threatened by CPB in the future. Simulations under scenario RCP6.0 additionally included the south of Poland (Katowice) as one of the region most at risk of CPB.

Comparison of SGCPBP obtained in simulations on real and transformed data also enables identification of the regions vulnerable to higher changes in SGCPBP. Based on scenarios RCP2.6, RCP4.5 and RCP6.0, the south of central Poland (Kielce) and the eastern part of Poland (Lublin) should be included into that category. The predicted increase in SGCPBP obtained in simulations under these scenarios for these two localities distinctly differs from the rest. According to simulation results from scenario RCP8.5, it appears that besides these two localities, another three (Białystok, Gdańsk and Olsztyn) are more vulnerable to increase in SGCPBP than other localities.

Considering the results of the study dealing with the risk of CPB third generation appearance, it seems that the south-western region (Opole), eastern region (Lublin) and southern part of central Poland (Kielce) may face the most problems caused by increased numbers of CPB generations.

Results obtained in the present study are also in line with predictions of CPB development under expected climate change in the Czech Republic presented by Kocmankowa et al. [28], who used a simulation performed with the use of the CLIMEX model to show a growing danger of an increase in the number of CPB generations. This is in line with the predictions by Menéndez [29], Das et al. [30] and Sangle et al. [31], who expected greater numbers of generation of so-called "stop and go" insects following climate change. Kocmankowa et al. [28] also predicted a widening of the area of CPB occurrence and a shifting of the pest to higher altitudes. The significant increase in SGCPBP in the Małopolska upland located in the southern part of central Poland (Kielce) showed in our study confirms the findings of Kocmankowa et al. [28]. Similar results were also presented by Pulatov et al. [32], who analyzed the effect of climate change on the potential spread of the Colorado potato beetle in Scandinavia. They showed a substantial increase in the frequency of years in which the temperature requirement for development of one generation was fulfilled. Additionally, they indicated regions where two generations per year may occur more often.

The results of the simulations performed by Žalud et al. [33] for middle Europe, including Poland, also show an increase in the number of CPB generations per year based on the temperature increase predicted by various scenarios. Possible increases in the number of CPB generations are also expected in some areas of Russia by Popova [34], who used cartographic modeling to show that this phenomenon is caused by an increase in the sum of effective air temperatures in those territories.

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The differences in the effect of climate change on CPB development between regions shown in the present study are also in consistent with the findings of Wittchen and Freyer [35], who analyzed the impact of temperature increases at two localities in Germany (Potsdam and Ulm) on the appearance of subsequent developmental stages of CPB. Simulations performed under real temperatures generated faster development of CPB first generation at Potsdam (30 m a. s. l.) than at Ulm (470 m a. s. l.) (by 5 days). But, under increased temperatures, CPB developed faster at Ulm than at Potsdam (by 3 days). A similar situation was noticed while comparing the development of CPB in Poland at Toruń (46 m. a. s. l.) and Kielce (270 m. a. s. l.). Using real data, development of CPB first generation at Toruń was 5 days shorter than at Kielce, while under transformed data and depending on the RCP scenario at Toruń development was 2–3 days longer than at Kielce.

The results of this study clearly indicate not only increased rates of CPB development following expected climate change across Poland, but also the regions exposed to the most rapid changes in the number of pest generations. But, one has to be aware that the interaction among the environmental factors is very complex and changeable. Most insect pests can adapt to a wide range of environments through selection and evolution. Therefore, prediction based on factor-limited simulations produce results with limited accuracy. On the other hand, only simulations can aid a rapid investigation of the effects of a change in a real life situation that will take place in the future over several years. From simulation results, a problem expected in the future can be mitigated now. So, systematic monitoring of potato crops in the regions indicated in the present study as the most threatened by the appearance of additional generations of CPB should be our first priority. Knowledge about pest trends gained in simulations coupled with results of field monitoring allows the determination of the feasibility of using certain pest management strategies.
