القا استرس اکسیداتیو و آسیب DNA توسط تنش دمایی در Orius laevigatus Fieber و Tetranychus urticae Koch

The anthocorid predator Orius laevigatus as biological control agent is widely used for controlling Tetranychus urticae which is one of the most destructive mites attacking crops. Many organisms critically are affected by environmental stressors such as temperature which by including physiological responses could affect their abundance, distribution, growth, and reproduction. Reactive oxygen species (ROS) overproduce under thermal stress, which can cause oxidative damage in the treated organisms. The balance between ROS production and antioxidant processes has been demonstrated. This balance can be disrupted under environmental stress, leading to synthesis of additional ROS. In general, the fluidity of cell membranes could be disrupted as a result of lipid peroxidation as well as alterations in cellular DNA followed by ROS overproduction. In this study, the effects of thermal stress (15, 25, and 35 °C) on DNA damage and oxidative stress in adults of the tetranychus mite and the anthocorid predator were assessed. Antioxidant enzyme including superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and malondialdehyde (MDA), were evaluated. In addition, single-cell gel electrophoresis (DNA comet assay) used to detect the thermal stress treatments on both the studied insects. Young anthocorid predator adults (< 2d old) were collected and placed in petri dishes (2 adults in a 10 mm in diameter) which each one was provided with a moisture source into a plastic dish (0.75 cm in diameter). Twenty bug adults treated with three consent temperature under laboratory conditions in incubator. The number of dead and alive predators were recorded, 24 h after treatment. Same experiments were conducted on T. urticae. Leaf discs (20 mm diameter) were prepared by punching leaves of 2-week-old kidney bean and were placed on wet cotton pads in plastic Petri dishes (10 mm diameter) which were treated under thermal conditions as explained above. 20 tetranychus mite adults (3- to 5-day old) were transferred each petri dish and after 24 h, the numbers of dead and alive mites were recorded. Five replicates were set up for each treatment in a randomized complete design. Conventional protocols were used to extract enzyme extracts of the anthocorid predator and tetranychus mite post treatments. The results showed that thermal stress treatments caused increasing DNA damage in the anthocorid predator and tetranychus mite. DNA damage at increasing exposure times was significantly larger than the control group (p>0.05). SOD, CAT, and GST activities decreased and MDA level increased in the treated groups compared to control group. No significant differences were found between the anthocorid predator and tetranychus mite post treatments. Our results confirmed that thermal stress could induce oxidative stress and proved to be DNA damage. Hence, thermal stress in environment may be used to determine potential physiological effects on the pest and beneficial insects.