Introduction
The leopard moth, Zeuzera pyrina L. (Lepidoptera: Cossidae), is a dangerous wood-boring insect that is considered the most important pest of the walnut (Kutinkova et al., Reference Kutinkova, Andreev and Arnaoudov2006; Saeidi et al., Reference Saeidi, Bagheri and Khalili-Moghadam2022), olive (Hegazi et al., Reference Hegazi, Khafagi, Konstantopoulou, Raptopoulos, Tawfik, Abd El-Aziz, Abd El-Rahman, Atwa, Aggamy and Showeil2009), and apple (Almanoufi et al., Reference Almanoufi, Chanan, Jamal, Lillo, Tarasco and Onghia2012) in Iran and other countries. The pest larvae cause serious damage to the trees by boring into the twigs, branches, and trunks, weakening and sometimes killing them (Kutinkova et al., Reference Kutinkova, Andreev and Arnaoudov2006; Hegazi et al., Reference Hegazi, Shlyter, Khafagi, Atwad, Agamy and Konstantopoulou2015; Saeidi, Reference Saeidi2020). Like other insects, the pest is a poikilothermic organism and the temperature of its body depends on the environmental temperature. According to Kocmánková et al. (Reference Kocmánková, Trnka, Juroch, Dubrovský, Semerádová, Možný, Žalud, Pokorný and Lebeda2010), temperature is probably the most important environmental factor affecting the population dynamics of insects. Temperature, precipitation, and humidity are the most important factors which affect the distribution and seasonal activity of insect pests under field conditions (Ullah et al., Reference Ullah, Haque, Nachman and Gotoh2012; Bayu et al., Reference Bayu, Ullah, Takano and Gotoh2017; Islam et al., Reference Islam, Jahan, Gotoh and Ullah2017; Shimazaki et al., Reference Shimazaki, Ullah and Gotoh2019). Moreover, many researchers reported that the population growth parameters of insects and mites such as developmental rate, survival, reproduction, and longevity vary with the climate factors (El-Halawany and Abdel-wahed, Reference El-Halawany and Abdel-wahed2013; Riahi et al., Reference Riahi, Shishehbor, Nemati and Saeidi2013).
Changes in temperature and other climate factors influence directly and indirectly agricultural crops and their corresponding pests (Skendžic et al., Reference Skendžic, Zovko, Zivkovic, Lesic and Lemic2021). Climate factors directly impact the pests’ life-table parameters, whereas they indirectly affect the relationships between pests, their host plants, environment, and other insect species (Prakash et al., Reference Prakash, Rao, Mukherjee, Berliner, Pokhare, Adak, Munda and Shashank2014). According to Liang and Elbakidze (Reference Liang and Elbakidze2011), there is a significant relationship between changes in environmental factors and pests outbreak. Various studies investigated the impact of climate changes on the distributions, migration, population changes, and damage of insect pests such as the onion thrips, Thrips tabaci Lindeman (Bergant et al., Reference Bergant, Trdan, Znidarcic, Crepinsek and Bogataj2005), Lepidoptera species (Sparks et al., Reference Sparks, Dennis, Croxton and Cade2007), the plain tiger, Anosia chrysippus L. (Sudan et al., Reference Sudan, Pervaiz and Tara2015), the peach twig borer, Anarsia lineatella Zeller (Saeidi, Reference Saeidi2019) and the leopard moth, Z. pyrina (Fekrat and Farashi, Reference Fekrat and Farashi2022).
Considering the importance of the climate variables, this research was undertaken to investigate the effect of climate factors on the population changes, damage and infestation area of the leopard moth in four different parts of Iran, including Chaharmahal va Bakhtiari, Kerman, Isfahan, and Markazi provinces which severely infested by Z. pyrina. The results may be useful to predict the pest population status in the future under climate change scenarios and to develop a successful integrated Z. pyrina management programme.
Materials and methods
Meteorological data
The climate factors studied were: average of annual mean temperature, annual mean minimum temperature, annual mean maximum temperature, annual absolute minimum temperature, annual absolute maximum temperature, mean temperature of January, February, July and August, mean temperature of autumn, winter, spring and summer, the number of frost days per year, annual relative humidity, and annual precipitation. Meteorological data of four synoptic stations in different provinces including Saman (Chaharmahal va Bakhtiari province), Najaf-Abad (Isfahan), Arak (Markazi), and Baft (Kerman) were obtained from Iran Meteorological Organization. The geographical coordinates of the studied orchards and their distance from the nearest station are given in table 1.
Table 1. Geographical coordinates of the studied orchards and their nearest synoptic stations
Seasonal activity of the pest
Seasonal flight of the adults was studied during 2006–2018 using sex pheromone traps. Two walnut orchards in each region, with 3–5 km distances apart, were selected. Walnut trees were approximately 15–20 years old, 13–14 m high, and planted at 10 × 8 m2 distances between and along the rows. No chemical was applied on experimental plots during the period of study. The pheromone dispensers, type of trap, and installation height were followed according to Saeidi (Reference Saeidi2020). Four sex pheromone-baited traps were installed in each orchard and to avoid interference between them, the distance between two adjacent traps was 50 m (Ardeh et al., Reference Ardeh, Mohammadipour, Kolyaee, Rahimi and Zohdi2014). All traps were set at a height of 1 m below the apical point of the trees’ canopy and leaves and branches were removed around their entrances (Saeidi et al., Reference Saeidi, Bagheri and Khalili-Moghadam2022). The traps were set-up in each location from 10 May (before the emergence of adult males) to 15 July (the end of the adults’ flight) to monitor the pest population. Pheromone traps were checked twice a week until the capture of first adult and then once a week to record the number of captured moths. The sticky sheets and the pheromone lures were replaced every 2 weeks and every month, respectively.
Twig infestation
Since the young larvae bore into twigs, the number of infested twigs/tree was determined in each orchard during the second week of August, when the activity of larvae was maximal on the twigs. For this purpose, 20 trees in each location were selected randomly and ten random twigs (60 cm length), from each side of the tree at mid height, were examined and the infestation ratio was calculated.
Number of active galleries/tree
The number of active galleries/tree was determined during the second week of October, when the 4th and 5th instar larvae bore into trunk and main branches. For this purpose, 20 trees in each orchard were selected randomly and the number of active galleries on the trunk (up to 4 m height) was recorded.
The infested areas
The areas infested (ha) by Z. pyrina in the studied provinces (including Chaharmahal va Bakhtiari, Isfahan, Markazi, and Kerman) were obtained from Plant Protection Organization, Ministry of Agriculture, Iran.
Trend analysis
The widely used Mann–Kendall test was run at 95% confidence level on time series data of both climate and pest population for the time period 2006–2018. According to this test, the null hypothesis, H0 assumes that there is no trend (the data are independent and randomly ordered) and this is tested against the alternative hypothesis H1, which assumes that there is a trend. If the P value is less than the significance level α (alpha = 0.05), H0 is rejected. Rejecting H0 indicates that there is a trend, while accepting H0 indicates no trend in the time series (Kendall, Reference Kendall1975; Pohlert, Reference Pohlert2016).
Software used for performing the statistical Mann–Kendall test was Addinsoft's XLSTAT 2018. In addition, to compare the results obtained from the Mann–Kendall test, linear trend lines are plotted using Microsoft Excel 2007. Pearson's correlation coefficient was used to determine the effect of climate factors on population changes and damage caused by the pest on walnut trees. Moreover, stepwise regression was used to find a set of climate variables that significantly influence the population and damage of Z. pyrina.
Results
Comparison of climate factors
Saman synoptic station: the average of annual mean temperature from 2006 to 2018 at Saman synoptic station was 13.63 ± 0.72°C (±SE), ranging from 11.75 to 14.94°C. Therefore the annual average temperature in the hottest year (2016) increased by 3.24°C compared to the coldest year (2013) (table 2). The same trend was observed in different months, especially in winter. January and February showed the highest increase (12.50 and 7.93°C, respectively) in temperature in the hottest year compared to the coldest one (table 2). The annual mean maximum temperature from 2006 to 2018 was 20.55 ± 0.28°C, ranging from 18.23 to 22.26°C (4.03°C difference), whereas the annual mean minimum temperature was 6.24 ± 0.34°C with a range of 2.95–7.63°C (table 2). The highest number of frost days was recorded during the 2006–2007 growing season (122 days) and the lowest during 2017–2018 (6 days). The lowest annual absolute minimum temperature (−21.8°C) corresponds to 2007–2008 and the highest (−6.8°C) to the growing period 2016–2017 (table 2). The annual rainfall ranged from 155.7 mm (in 2017–2018) to 511.40 mm (in 2007–2008), with a mean of 298.70 ± 26.42 mm. The mean annual relative humidity was 34.73 ± 0.73% with a range of 30.95–37.80% (table 2).
Table 2. Mean of different climate variables in the studied synoptic stations from 2007 to 2018
Arak synoptic station: the annual mean temperature, annual mean maximum temperature, and annual mean minimum temperature from 2006 to 2018 were 14.80 ± 0.51, 20.83 ± 0.55, and 8.39 ± 0.49°C, respectively. The highest and the lowest number of frost days were 105 and 31, respectively. The lowest annual absolute minimum temperature (−12.8°C) corresponds to 2007–2008 and the highest (−6.8°C) to the growing period 2016–2017 (table 2). The mean annual rainfall during this period was 298.70 ± 26.42 mm, ranging from 166.80 mm (in 2016–17) to 499.70 mm (in 2014–15). The mean annual relative humidity was 43.50 ± 0.76% with a range of 39.80–78.80% (table 2).
Baft synoptic station: the annual mean temperature, annual mean maximum temperature, and annual mean minimum temperature were 15.24 ± 0.18, 23.32 ± 0.70, and 7.45 ± 0.74°C, respectively (table 2). The highest increase in annual mean, maximum, and minimum temperatures were observed in the winter season (January and February). The highest number of frost days was recorded during 2006–2007 (81 days), whereas the lowest was related to 2016–2017 (37 days). The lowest annual absolute minimum temperature (−12.00°C) was observed in 2007–2008 and the highest (−6.00°C) in the growing period 2017–2018 (table 2). The mean annual rainfall was 251.90 ± 23.64 mm, with a range of 134.3 mm (in 2007–2008) to 467.20 mm (in 2017–2018). The mean annual relative humidity was 35.71 ± 1.11% with a range of 31.60–45.40% (table 2).
Najaf-abad synoptic station: the annual mean temperature, annual mean maximum temperature, and annual mean minimum temperature were 16.70 ± 0.20, 24.10 ± 0.20, and 9.50 ± 0.20°C, respectively (table 2). Similar to the other stations, the largest increase in mean, maximum, and minimum annual temperatures occurred in winter. The number of frost days ranged from 89 days (in 2006–2007) to 13 days (in 2017–2018). The lowest annual absolute minimum temperature (−12.20°C) corresponds to 2007–2008 and the highest (−5.00) to the growing season 2016–2017 (table 2). The annual rainfall was 120.90 ± 14.60 mm ranging from 47.90 mm (in 2007–2008) to 193.70 mm (in 2012–13). The mean annual relative humidity was 34.40 ± 1.00% with a range of 30.70–42.10% (table 2).
Changes in the population of the leopard moth
Saman (Chaharmahal va Bakhtiari): the average number of moths caught (in each trap), the percentage of infested branches/tree (in August), the number of active galleries/tree (in November), and the infested areas (ha) during the studied period (2006–2018) were 49.83 ± 4.84 (±SE), 57.91 ± 4.02, 37.83 ± 4.97, and 566.6 ± 89.53, respectively. The highest number of moths caught (per trap) was observed in the growing season 2017–2018, whereas the lowest occurred in 2006–2007 and 2012–2013. A similar trend was observed in the percentage of infested branches and the number of active holes/tree. The infested areas by the pest increased from 100 ha (in 2006–2007) to 1100 ha in 2017–2018 growing season (table 3).
Table 3. Mean number of moths caught (in each trap), the percentage of infected branches/tree (in August), the number of active holes/tree (in November), and the infested areas (ha) in different locations during the studied period 2006–2018
Baft (Kerman province): the average number of moths caught (in each trap), the percentage of infested branches/tree (in August), the number of active galleries/tree (in November), and the infested areas (ha) during the studied years (2006–2018) were 39.41 ± 3.30, 45.41 ± 3.83, 3.13 ± 0.26, and 256.60 ± 26.02, respectively. The highest number of moths caught (in each trap) was observed in growing season 2010–2011 and the lowest in 2006–2007. The highest percentage of infested branches and the number of active holes/tree were observed in 2007–2008 and 2009–2010, respectively. Similar to the Saman station, the infested walnut orchards increased from 75 ha (in 2006–2007) to 360 ha in 2017–2018 growing season (table 3).
Arak (Markazi province): the average number of moths caught (in each trap), the percentage of infested branches/tree (in August), the number of active galleries/tree (in November), and the infested areas (ha) during the studied years (2006–2018) were 90.67 ± 5.88, 24.33 ± 2.35, 3.92 ± 0.89, and 670.80 ± 57.72, respectively. The highest number of moths caught (in each trap) was observed in growing season 2017–2018 and the lowest in 2007–2008. The highest percentage of infested branches and the number of active holes/tree were observed in 2017–2018. The infested areas increased from 350 ha (in 2006–2007) to 900 ha in 2017–2018 growing season (table 3).
Najaf-abad (Isfahan province): the average number of moths caught (in each trap), the percentage of infected branches/tree (in August), the number of active galleries/tree (in November), and the infested areas (ha) during the studied years (2006–2018) were 54.30 ± 4.80, 52.90 ± 4.20, 6.70 ± 0.40, and 495.00 ± 52.30, respectively. The highest number of moths caught (in each trap) was observed in the growing season 2017–2018 and the lowest in 2006–2007. Moreover, the highest percentage of infested branches and the number of active galleries/tree were observed in 2017–2018. As in the other regions, the area of infested walnut orchards increased from 270 ha (in 2006–2007) to 800 ha in 2017–2018 (table 3).
Trends in the climate variables
Saman: in the studied period (2006–2018), the mean temperature of the annual, winter, and autumn seasons showed increasing trends, while the average temperature of summer and spring had no trend. Kendall's statistics (T) for the mean temperature of annual, spring, summer, autumn, and winter were 0.64, 0.25, 0.34, 0.53, and 0.59, respectively. Therefore, the largest warming occurred in autumn (T = 0.53) and winter (T = 0.59) seasons (table 4). Moreover, there were significant increasing trends in annual mean minimum temperature, annual mean maximum temperature, annual absolute minimum temperature, and mean temperatures of January and February (Kendall statistics were 0.61, 0.60, 0.64, 0.42, and 0.48, respectively), whereas the annual absolute maximum temperature and the mean temperatures of July and August showed no trend. Among the studied months, the largest increase occurred in January temperature (tables 2 and 4). Moreover, the number of annual frost days showed a decreasing trend (T = −0.63) in the studied period (2006–2018).
Table 4. Mann–Kendall trend analysis of time series data of climate variables for the time period 2006–2018
Arak: the number of annual frost days and percentage of mean annual humidity showed decreasing trends (T = − 0.63 and −0.48) in the studied period (2006–2018), whereas the annual absolute minimum temperature, annual mean minimum temperature, and the mean temperature of January showed increasing trends (Kendall statistics were 0.53, 0.41, and 0.45, respectively). Moreover, two peaks were observed in the studied period, the first one occurring from 2006 to 2012 and the second occurring from 2013 to 2018. Statistical analysis showed increasing trends in the mean temperatures of annual, minimum, maximum, January, and February (table 4).
Baft: in this station, the number of annual frost days and percentage of mean annual relative humidity showed decreasing trends (T = −0.61 and −0.64), whereas the other studied factors showed no trend in the studied period (table 4).
Najaf-abad: the number of annual frost days and percentage of mean annual humidity showed decreasing trends (T = −0.61 and −0.41), whereas the mean temperatures of annual, minimum, and January showed increasing trends (T = 0.48, 0.42, and 0.61) in the studied period (table 4).
Trends in the population of the leopard moth
In Saman and Najaf-abad stations, significant increases were observed in the mean number of moths caught (in each trap), the percentage of infested branches/tree (in August), the number of active galleries/tree (in November), and the infested areas (ha) during the studied years (2006–2018). The Kendall statistics in the Saman station were calculated as 0.59, 0.66, 0.79, and 0.98, respectively, whereas in the Najaf-abad they were 0.90, 0.90, 0.68, and 0.98, respectively (table 5).
Table 5. Mann–Kendall trend analysis of time series data of Z. pyrina L. population and damage for the time period 2006–2018
In Arak, the mean number of moths caught (in each trap), the percentage of infested branches/tree (in August), the number of active galleries/tree (in November), and the infested areas (ha) showed increasing trends (Kendall statistics were 0.76, 0.58, 0.55 and 0.73, respectively). In the Baft station, the infested areas (ha) showed an increasing trend, whereas there was no trend for the mean number of moths caught (in each trap). Moreover, a decreasing trend was observed for the percentage of infested branches/tree (in August) and the number of active galleries/tree (in November) (table 5).
Relation between climate factors and population and damage of Z. pyrina
Saman (Chaharmahal va Bakhtiari province): according to the results, there was a positive and significant relation between the number of trapped male moths and temperature (especially the annual mean temperature, annual mean maximum temperature, mean temperature of January, autumn, and winter seasons), while negative and significant relations were observed between the pest population and the number of frost days (r = −0.52) and the annual relative humidity (r = −0.80). Moreover, increasing annual absolute minimum (r = 0.69) and absolute maximum temperatures (r = 0.78) had positive and significant effects on the percentage of infested branches (figs 1–4).
Figure 1. Relation between annual mean temperature and population and damage of Z. pyrina L. in the studied areas.
Figure 2. Relation between January mean temperature and population and damage of Z. pyrina L. in the studied areas.
Figure 3. Relation between the number of frost days and population and damage of Z. pyrina L. in the studied areas.
Figure 4. Relation between annual relative humidity and population and damage of Z. pyrina L. in the studied areas.
The relation between the number of active galleries/tree (in November) and the number of frost days (r = −0.56) and the annual relative humidity (r = −0.74) was significantly negative, whereas the relation between the number of active galleries/tree and the temperature variables (including annual mean temperature, annual mean maximum temperature, the average temperature of January, autumn, and winter seasons) were significantly positive. The pest-infested area was positively correlated with temperature (especially the annual absolute minimum temperature, mean annual temperature, mean maximum temperature, and average temperatures of January, February, autumn, and winter) and negatively correlated with frost days and relative humidity.
Stepwise regression analysis showed that among the different climate variables, the mean temperature of January and mean annual humidity were the most statistically significant variables on the number of trapped male moths (r = 0.88, r 2 = 0.77, F(2, 8) = 13.52, sig. 0.003) and number of galleries/tree (r = 0.85, r 2 = 0.73, F(2, 8) = 10.87, sig. 0.005). Moreover, the mean temperatures of January and autumn, and annual mean maximum temperature (r = 0.99, r 2 = 0.98, F(3, 7) = 100.48, sig. 0.0001) were most closely related to the percentage of infested branches, while the area of infested orchards (ha) was most closely correlated with the annual absolute minimum temperature (r = 0.72, r 2 = 0.52, F(1, 9) = 9.88, sig. 0.012).
Baft (Kerman province): there was no significant relation between mean temperature (annual, maximum, and minimum) and the pest population and damage, whereas the number of frost days (r = −0.56) and percentage of annual relative humidity (r = −0.74) were negatively correlated with the mean number of moths caught (r = −0.48 and r = −0.76), the percentage of infested branches/tree (r = −0.58 and r = −0.63), and the infested areas (r = −0.68 and r = −0.70, respectively) (figs 1–4).
In stepwise regression analysis, mean annual relative humidity and annual mean minimum temperature were most closely related to the number of trapped male moths (r = 0.62, r 2 = 0.38, F(1, 10) = 6.13, sig. 0.03) and the number of galleries/tree (r = 0.82, r 2 = 0.67, F(1, 10) = 20.10, sig. 0.001), respectively. Moreover mean temperature of January and mean annual relative humidity were most closely related to the number of infested branches/tree (r = 0.91, r 2 = 0.82, F(2, 9) = 20.10, sig. 0.0001), whereas the annual mean maximum temperature was most closely related to the area infested (r = 0.81, r 2 = 0.81, F(1, 10) = 43.92, sig. 0.0001).
Arak (Markazi province): the relations of the mean number of moths caught (per trap), the percentage of infested branches/tree, the number of active galleries/tree, and the infested areas with the number of frost days (r = −0.55, −0.66, −0.56, and −0.61) and annual relative humidity (r = −0.85, −0.62, −0.78, and −0.73, respectively) were significantly negative. Moreover, by increasing the temperature (especially the annual mean temperature, the annual mean maximum temperature, the mean temperature of January and February), the number of active galleries/tree, and the infested areas were significantly increased (figs 1–4). The number of frost days was the most significant variable fitting the regression model of Z. pyrina infested areas (r = 0.67, r 2 = 0.44, F(1, 10) = 7.96, sig. 0.018).
Najaf-abad (Isfahan province): there were negative and significant relations between the number of trapped male moths and the number of frost days (r = −0.61) and per cent of annual relative humidity (r = −0.56). Moreover, the relations of mean annual relative humidity with the percentage of infected branches/tree (r = −0.69), the number of active galleries/tree (r = −0.53), and the infested areas (r = −0.93) were significantly negative. Moreover, mean temperatures of annual, minimum, and January had significant and positive correlation with the population, damage (per cent of infected branches and the number of active galleries/tree), and infestation area of Z. pyrina (figs 1–4). According to stepwise regression analysis, the mean temperature of January was the best-fitted variable in regression models of the number of trapped male moths (r = 0.73, r 2 = 0.54, F(1, 10) = 11.72, sig. 0.007) and the number of infested branches/tree (r = 0.72, r 2 = 0.52, F(1, 10) = 10.74, sig. 0.008), whereas the mean annual relative humidity was most closely related to the number of active galleries/tree (r = 0.59, r 2 = 0.34, F(1, 10) = 5.28, sig. 0.04). For the pest-infested areas (ha), the mean temperature of January, and annual absolute maximum temperature had the strongest relationship (r = 0.83, r 2 = 0.69, F(2, 9) = 9.81, sig. 0.005).
At a result, among the studied climate factors, the mean temperature of January, the mean temperatures of autumn and winter seasons, and the annual mean maximum temperature had positive correlations with Z. pyrina population size and damage in the walnut orchards, whereas percentage of relative humidity and the number of frost days had negative correlations.
Discussion
Climate factors, temperature and precipitation in particular, have strong influences on the development, reproduction, and survival of insect pests; therefore these organisms are affected by any change in the climate factors (Petzoldt and Seaman, Reference Petzoldt and Seaman2006; Skendžic et al., Reference Skendžic, Zovko, Zivkovic, Lesic and Lemic2021). Our results suggested that climate factors strongly affected the population and damage of Z. pyrina in the studied areas. The pest population significantly increased with increasing temperature and decreasing relative humidity and number of frost days. It was reported that climate factors (especially temperature, precipitation, and humidity) were the most important factors which influence insects' and mites' life-table parameters, their distribution, and seasonal activity under field conditions (Ullah et al., Reference Ullah, Haque, Nachman and Gotoh2012; Bayu et al., Reference Bayu, Ullah, Takano and Gotoh2017; Islam et al., Reference Islam, Jahan, Gotoh and Ullah2017; Saeidi and Nemati, Reference Saeidi and Nemati2017, Reference Saeidi and Nemati2020; Shimazaki et al., Reference Shimazaki, Ullah and Gotoh2019). Moreover, they indirectly influence the pests through changes in the physiology or existence of their host plants (Prakash et al., Reference Prakash, Rao, Mukherjee, Berliner, Pokhare, Adak, Munda and Shashank2014). Rouault et al. (Reference Rouault, Candau, Lieutier, Nagleisen, Martin and Varzee2006) reported that populations of bark beetles (Ips typographus L. and Pityogenes chalcographus L.) in the Western Europe forest were positively influenced by prolonged water stress and high temperatures and indirectly through physiological changes and decline of host resistance. According to Yihdego et al. (Reference Yihdego, Salem and Muhammed2019), plants stressed by drought are more susceptible to insect attack because of a decrease in the production of secondary metabolites that have a defence function. In another study, Ahmed et al. (Reference Ahmed, Mamun, Hoque and Chowdhury2012) reported that climate factors such as temperature, relative humidity, and sunshine hours were positively related to the infestation of red spider mites in Bangladesh tea orchards, whereas heavy rainfall, cloud coverage, and water requirement of the crop were negatively correlated with the mite infestation. Moreover, the effect of changes in temperature and humidity was reported on the development and outbreak of spider mites (Mandal et al., Reference Mandal, Sattar and Banerjee2006; Kumar et al., Reference Kumar, Raghuraman and Singh2015), bark beetles (Bentz et al., Reference Bentz, Regniere, Fettig and Hansen2010; Yihdego et al., Reference Yihdego, Salem and Muhammed2019), whiteflies (Pathania et al., Reference Pathania, Verma, Singh, Arora and Kaur2020), T. tabaci (Bergant et al., Reference Bergant, Trdan, Znidarcic, Crepinsek and Bogataj2005), and peach twig borer, A. lineatella (Saeidi, Reference Saeidi2019; Erhaft et al., Reference Erhaft, Saeidi and Shakarami2021).
Our results indicated significant trends in the studied climate factors during 2006–2018. Mean temperatures of annual, different seasons, and months showed significant and increasing trends, whereas the number of annual frost days indicated a decreasing trend. Trend analysis is one of the most important statistical methods used to evaluate the potential effects of climate change on time series data (such as temperature, precipitation, population, etc.). In this study, we used the Mann–Kendall method which is a non-parametric statistical test proposed by the World Meteorological Organization in trend analysis of climate series (Nicholson and Palao, Reference Nicholson and Palao1993; Xu et al., Reference Xu, Tkeuchi and Ishidaria2003; Pohlert, Reference Pohlert2016).
The phenomenon of climate change and increasing temperature, or global warming, is due to human activities which produce greenhouse gases (IPCC, 2022). The global annual temperature has increased at an average rate of 0.2–0.3°C per decade over the 20th century; therefore the Earth could experience global warming of 1.4–5.8°C over the next century (IPCC, 2022). Our results indicated an increasing trend in the temperature of the studied meteorological synoptic stations during the studied period (2006–2018). According to Skendžic et al., (Reference Skendžic, Zovko, Zivkovic, Lesic and Lemic2021) global climate warming could trigger an expansion of insect geographic range, increased overwintering survival, increased number of generations, increased risk of invasive insect species, and insect-transmitted plant diseases, as well as changes in their interaction with host plants and natural enemies (Skendžic et al., Reference Skendžic, Zovko, Zivkovic, Lesic and Lemic2021).
Among the studied temperature variables, increasing the minimum temperature (especially in the winter and autumn seasons) appears to be an important factor influencing Z. pyrina population. Hill (Reference Hill1987) reported winter as the most critical season for many insect pests, as low temperatures can significantly increase mortality and thus reduce populations in the following season (Hill, Reference Hill1987). Studies have shown that global warming is most pronounced in winter at high latitudes (Pachauari and Reisinger, Reference Pachauari and Reisinger2007). Therefore, insects that undergo winter diapause are experiencing the greatest changes in their thermal environment (Bale and Hayward, Reference Bale and Hayward2013). Z. pyrina overwinters as larvae inside the trunk and the main branches of walnut trees (Radjabi, Reference Radjabi2002; Kolyaee and Hassani, Reference Kolyaee and Hassani2014), therefore, winter mortality is critical in the transition to the next generations. According to Reddy et al. (Reference Reddy, Shi, Hui, Cheng, Ouyang and Ge2015), the warmer winter reduces the mortality of the cotton bollworm, Helicoverpa armigera Hübner, over-wintering stages, and as a result, its population increases sharply in the next season. Based on the evidence obtained from fossils, the insect species diversity and their feeding intensity have a direct relationship with temperature (Kujawski, Reference Kujawski2011). Another effect of rising temperature is on biological activities and the number of pest generations. Saeidi et al. (Reference Saeidi, Bagheri and Khalili-Moghadam2022) showed that Z. pyrina could complete its life cycle within a year in Chaharmahal va Bakhtiari province, Iran. According to other researchers, some individuals require 1 year but others may require 2 years to complete their development (Esmaili, Reference Esmaili1991; Radjabi, Reference Radjabi2002; Kutinkova et al., Reference Kutinkova, Andreev, Subchev and Rama2009; Kolyaee and Hassani, Reference Kolyaee and Hassani2014; Hegazi et al., Reference Hegazi, Shlyter, Khafagi, Atwad, Agamy and Konstantopoulou2015; Besharatnejad et al., Reference Besharatnejad, Ostuwan, Nematollahi and Rajabi2016). Our results showed the increasing autumn temperature allows Z. pyrina larvae to feed until the end of November and warmer winter increases their survival. Moreover, increasing the spring and summer temperatures favour faster development and emergence of Z. pyrina adults. According to reports, temperature is the most important climate variable that affects the behaviour, population dynamics, distribution, growth and development, survival, and reproduction of insects and mites (Petzoldt and Seaman, Reference Petzoldt and Seaman2006; Skendžic et al., Reference Skendžic, Zovko, Zivkovic, Lesic and Lemic2021). Rising temperatures may increase the survival of overwintering stages of insects at higher altitudes, and lead to the expansion of their geographic range (Pareek et al., Reference Pareek, Meena, Sharma, Tetarwal, Kalyan, Meena, Kumar, Kanwat, Meena, Kumar and Alone2017).
Our results demonstrated that the area (ha) infested by Z. pyrina significantly increased from 2006 to 2018. According to FAO (2020), climate change creates new ecological niches that provide opportunities for insect pests to establish and spread in new geographic regions and shift from one region to another. The spread of crop pests across physical and political boundaries increases the percentage of crop losses and threatens food security in different parts of the world (Fand et al., Reference Fand, Kamble and Kumar2012; FAO, 2020). For many pest species, a pole-ward shift in distribution is predicted as a response to global warming (Bebber et al., Reference Bebber, Ramotowski and Gurr2013, Fekrat and Farashi, Reference Fekrat and Farashi2022). For example, in Europe, the European corn borer (Ostrinia nubilalis Hubner) has shifted more than 1000 km northwards (Porter et al., Reference Porter, Parry and Carter1991), and the pink bollworm, Pectinophora gossypiella Saunders (Gutierrez et al., Reference Gutierrez, D'Oultremont, Ellis and Ponti2006) and the olive fly, Bactrocera oleae Rossi (Gutierrez et al., Reference Gutierrez, Ponti and Cossu2009) are expanding northwards due to the effects of increasing temperatures in Europe and America. According to Fekrat and Farashi (Reference Fekrat and Farashi2022), under future climate conditions, the risk areas of Z. pyrina in the Northern and Southern Hemispheres are expanding northwards and southwards, respectively.
In conclusion, climate variables especially rising temperatures appears to strongly impact the population and damage of Z. pyrina in walnut orchards. Therefore, our findings are useful for agricultural experts and farmers to predict the pest population and damage in the next years under climate change scenarios and develop a successful integrated Z. pyrina management programme to reduce the pest-induced crop losses. Moreover, knowledge about changes in seasonal activity, population dynamic, and distribution of Z. pyrina are necessary to develop more efficacious control methods such as pheromone traps (for monitoring, mass trapping, or mating disruption), cultural techniques (decreasing drought stress and time of removing infested branches), and insecticides application at the proper time and dosage. According to Skendžic et al., (Reference Skendžic, Zovko, Zivkovic, Lesic and Lemic2021) and Fekrat and Farashi (Reference Fekrat and Farashi2022), as climate change exacerbates the pest problem, there is a great need for developing new pest management strategies in the future. These include the development of more efficacious integrated pest management tactics, monitoring climate and pest populations, and the use of modelling prediction tools.
Acknowledgements
Financial support provided by the Agricultural and Natural Resources Research, Education & Extension Organization, Iran is gratefully acknowledged. The authors wish to thank Dr F. Raeisi, English teacher at the University of Applied Science and Technology, Shahrekord, Iran for editing of the manuscript.
Author contributions
Z. S. designed the experiments, analysed data, and wrote the manuscript. Material preparation and data collection in Chaharmahal va Bakhtiari, Kerman, Isfahan, and Markazi provinces were performed by Z. S., H. Z., M. H. B.-N., and M. Y., respectively. The authors read and approved the manuscript.
