Bottom-up population regulation of Orthotomicus erosus on irrigated and fertilized Pinus eldarica: A comprehensive field study

Abstract

The Mediterranean pine engraver, Orthotomicus erosus (Wollaston), is a destructive pest that has caused a significant threat to planted pine forests worldwide through feeding on phloem, disrupting sap flow and transmitting phytopathogens. This study investigated the bottom-up effects of different irrigation and fertilization treatments on the mean numbers of O. erosus immature stages (egg, larva and pupa) and adults in the pine forest of western Tehran, Iran. A total of 72 Pinus eldarica Medw. trees were selected in Chitgar Forest Park. The experiment was arranged as a split plot in a randomized complete block design with three replications. The irrigation treatments included non-irrigation, low-irrigation (30 liters of water per month) and high-irrigation (30 liters of water per two weeks) were assigned to main plots. Moreover, fertilizers of nitrogen 100 kg/ha, superphosphate 100 kg/ha and potassium sulfate 65 kg/ha were applied in subplots. Then, the total number of O. erosus life stages was counted under the bark samples (two 10 × 10 cm bark samples) separated from the pine trees. Results showed that irrigation and fertilization significantly affected the mean number of O. erosus from egg to adult stages. Irrigation had a more pronounced effect on the pest population than fertilization. The highest number of different life stages occurred in non-irrigated pines regardless of fertilization. Moreover, fertilizer effects were influenced by irrigation, where high irrigation negatively affected superphosphate + potassium sulfate fertilized pines and significantly increased the mean numbers of different O. erosus life stages compared to low-irrigation treatment. The lowest mean number of egg (11.95 ± 0.17), larva (8.62 ± 0.21), pupa (10.38 ± 0.13) and adult (9.04 ± 0.23) per bark samples occurred in superphosphate + potassium sulfate at low-irrigation plots. Interestingly, nitrogen fertilization increased pest density compared to unfertilized trees. Furthermore, despite the low mean number of different O. erosus life stages in superphosphate + potassium sulfate treatments, the nitrogen combination increased the pest density in both low and high-irrigation plots. These findings highlighted the importance of considering the interaction between irrigation and fertilizer types in the integrated pest management program for O. erosus.