Defoliation Effects of Pistachio Processionary Bud Moth (Thaumetopoea solitaria) larvae on Two Anacardiaceae Genus in North of Iraq

Defoliation by Pistachio Processionary Bud Moth Thaumetopoea solitaria (Freyer) larvae threatens many tree species, especially pistachio trees in Mediterranean countries, including the Kurdistan Region in the northern part of Iraq. This study examines severe defoliation caused by T. solitaria larvae on three tree species: Pistacia vera, P. khunjuk, and Rhus coriaria in the Haybat Sultan Mountains of Koya District, Erbil, Iraq. Female moths lay their eggs on host trees. After the eggs hatch in early spring, during bud swelling. The larvae begin feeding on leaves, green tissues, and unopened buds. Results show that the larvae feed on new foliage, causing significant damage. Pistacia vera exhibited significantly higher defoliation during the first through fourth larval stages. As the larvae progress to later instars, they consume larger, mature leaves, further worsening tree injury. By the fifth instar, larvae feed throughout the night, leading to complete defoliation, especially in Rhus coriaria, which showed significantly greater defoliation (p ≤ 0.05) compared to Pistacia vera and P. khinjuk, which recorded the lowest defoliation (671.1 cm²). Results also show that larvae consumed 1699.9, 1516.5, and 752.5 cm² of R. coriaria, P. vera, and P. khunjuk, respectively, over all larval stages. These data highlight R. coriaria as the most affected species and are essential for understanding tree vulnerabilities and developing effective pest management strategies. Defoliation rates showed significant variation among the studied species, where R. coriaria had the highest rates, particularly in the later stages, while P. khunjhuk had the lowest at the end. A positive and significant relationship was observed between the number and area of defoliated leaves across all studied species.