Effects of Cardinal Direction on Distribution and Populational Dynamism of Oak Leaf Roller (Tortrix viridana L.) on Quercus infectoria Oliv. and Q. libani Lindl.

• Main Authors: mohammadreza zargaran, Mohammad Jamshidi, Seyed Rostam Mousavi Mirkola
• Format: Article
• Language: fas
• Published: Ferdowsi University of Mashhad 2018-01-01
• Series: Majallah-i ḥifāẓat-i giyāhān
• Subjects: Pest, oak, population, forest, damage
• Online Access: https://jpp.um.ac.ir/index.php/jpp/article/view/56354

Introduction Various pests attack oak trees and in most cases heavily damage them. The European oak leaf roller is one of the important oak pests in some provinces of the Zagros, and it is an important pest of oak forests in some European and North African countries, as well as in Iraq and other regions of Iran. In Iran, it is scattered in the Zagros oak forests, especially in Kohkiluyeh and Boyer Ahmad, Lorestan, Chahar Mahal and Bakhtiari, Fars, and West Azarbaijan Provinces. Repeated removal of oak leaves, particularly by herbivores such as T. viridana in spring, reduces stored photosynthates in trees leading to their decreased diametrical growth. Materials and Methods The Ghabre-Hossein region (Piranshahr) was selected as the field operations region because it is one of the most important infestation centers of the European oak leaf roller in the oak forests of West-Azerbaijan. The research was carried out in two consecutive years. Samples of larval instars were taken in early May. Since the sample plot in sampling methods can be points or lines (transects), the four cardinal directions were selected in this study and transects at 100 m intervals were located in each direction.To reduce sampling error, Aleppo (Quercus infectoria) and Lebanon (Q. libani) oak trees were selected for measurements that were similar in appearance and almost uniform with crowns or trunks aligned along the transects. In each studied tree, four suitable branches were selected (one in each cardinal direction), and the number of larvae from the tip of each branch to a length of 50 cm inwards was counted and recorded in forms prepared beforehand. Considering studies that were carried out regarding the biology of the pest, the larvae were counted in mid-May when all larvae were in their last (fifth) instar. In all, 30 Aleppo and 30 Lebanon oak trees were selected in each cardinal direction, and four branches in each direction of these trees were measured. The survey method was used by employing a 25 m rope, a slope gauge, and a compass to locate the sampling transects. SPSS 18 and the 2×4 factorial split plot in time design were used as the statistical method for studying the effects of various cardinal directions and of oak species on abundance of the European oak leaf roller, and Tukey’s HSD test was employed for comparison of the means. Results and Discussion This pest has a single annual generation and five larval instars. It overwinters, and spends the entire summer, autumn, and winter, as eggs. Eggs are hatch in late March. Larvae pierce buds to enter into and feed inside them, and large larvae can leave buds and start feeding on other buds. The results showed that in both years the number of leaf-roller moth larvae were more on Q. infectoria in comparison to Lebanon oaks and it seems that oak species (Q. infectoria) is more preferable for the pest to feed upon than Lebanon oaks. Studying populational changes of the oak leaf-roller moth in the geographical directions proved that for both of the tree species the maximum and the minimum number of larvae were respectively in the east and the west in 2014. In 2015, it also became clear that the highest and the lowest frequency of the larvae were respectively in the south and the north. The obtained results confirmed the influence of wind direction on distribution orientation of leaf-roller moth larvae. The number of oak leaf-roller moth larvae significantly increased in 2015 in comparison to the previous year which can be due to the temperature increase in this year. Conclusions The number of larvae of the European oak leaf roller on Aleppo oak trees was larger compared to Lebanon oak trees both in 2014 and in 2015, which shows this pest prefers Aleppo oak trees over Lebanon oak trees as its food supply. The number of larvae on both oak species in 2015 was considerably larger compared to the previous year, which may have been caused by increased temperatures in 2015. Study of population changes of the pest in the cardinal directions indicated that the maximum and minimum numbers of larvae on both oak species in 2014 were observed in the eastern and western cardinal directions, respectively, and that the maximum larval concentration occurred in the eastern direction of tree crowns. The dominant wind in the region blew from the southwest, and seemed to be the main reason why larval concentration and distribution occurred in the eastern direction (that was not influenced by wind currents). In 2015 also, the maximum and minimum abundance of larvae were observed in the southern and northern cardinal directions, respectively. Moreover, the largest larval concentration occurred in the northern direction of tree crowns, with the dominant wind in the region blowing in the northeast direction, which demonstrated the direct influence of wind on the orientation and distribution of the European oak leaf roller population. Results obtained in 2014 and 2015 showed that orientation and distribution of the European oak leaf roller can be influenced by wind direction and temperature.